Download PHYSICAL GEOLOGY LECTURE NOTES, PAGE I. Introduction

PHYSICAL GEOLOGY LECTURE NOTES, PAGE 1
I. Introduction
Geology - the study of the Earth
Physical Geology - study of Earth materials, such as minerals and rocks, and the various physical
and chemical changes that occur on its surface and in its interior
Historical Geology - history of the planet and its life forms from its origin to the present
A. Earth Materials
1. Minerals
- naturally occurring inorganic solids with definite chemical compositions and crystalline
structure
- the "building blocks" of rocks
2. Rocks
- naturally occurring substances made of minerals or mineraloids (mineraloids have a definite
chemical composition but are atomically structureless)
- rocks have a high variability in composition and particle size, shape and arrangement (texture)
3. Commodities
- the "value" of geology
a. Fossil fuels
- include coal, petroleum and natural gas
b. Mineral Resources
- include metals and other usable Earth materials
B. What Geologists Study:
1. Mineralogy
- study of minerals
2. Petrology
- study of rocks
Volcanology (Vulcanology) - study of volcanoes
3. Geochemistry
- study of the chemistry of minerals, rocks and water
4. Geophysics
- study of the physics of the Earth; including studies of earthquakes (seismology), Earth
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magnetism, Earth gravity, heat transfer, tectonics (movement and deformation of the Earth's
crust) and orogenic activity (mountain building)
5. Geomorphology and Sedimentology
- the study of "landforms" (geomorphology) including rivers and streams, landforms built by
"mass wasting" (downslope movement of material by gravity), underground water, moving ice
(glaciers), wind, and chemical activity and the rocks resulting from such activity (sedimentary
rocks)
6. Geochronology
- study of "Earth Time" (Geochronology) including studies of stratigraphy (rock layers), absolute
dating techniques (gives date in years) and studies of ancient life (paleontology)
7. Economic Geology
- exploration and exploitation of economic minerals and hydrocarbons
8. Hydrogeology/Hydrology
- geology of surface and underground water (groundwater) resources
9. Environmental Geology
- protection and proper utilization of Earth resources
- involves studies of engineering geology, hydrogeology, geomorphology, geochemistry and
geophysics
C. The Birth of Modern Geology
1. James Hutton (1726 - 1797)
- Scottish gentleman farmer and geologist; the "Father of Geology"
- formulated the concept of "Uniformitarianism"
a. Uniformitarianism
- "the present is the key to the past"
- the Earth is shaped by daily, mundane processes
- the Earth is very old
- believed that "great catastrophes" have only minor influence
2. More recent studies use the concept of Actualism
a. Actualism
- apply studies of modern processes to ancient rocks
- the processes that now shape the Earth were similar in the geologic past, although the rate of
change may vary
- recognizes that "catastrophes" can have powerful influence on the Earth
3. Geologic Time
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a. Early concepts of time were based on religion
- Archbishop James Ussher (1580-1655) of Ireland stated that the Earth originated in 4004
B.C.E., based upon the genealogies of the biblical patriarchs
- John Lightfoot (1602-1675), an English theologian, "refined" this estimation to state that the
Creation occurred at 9 A. M. on Sunday, October 23rd, 4004 B.C.E.
b. Geologic Time Scale
- the Earth is 4.6 billion years old
- the subdivisions of the time scale are based primarily on the predominant life forms living
during specific times
II. Geologic Time and Fossils
A. Types of Geologic Time
1. Relative Geologic Time
- placing geologic events in chronological order
- primarily use fossil studies (paleontology) and the study of rock layers (stratigraphy)
2. Absolute (Actual) Geologic Time
- date geological events in years
- use wide variety of dating techniques, especially radiometric (radioactive) dating
B. Fossils
- remains of preexisting life
1. How Geologists Use Fossils
a. For determining Relative Geologic Time
Law of Faunal Succession - organisms change through time; each life form corresponds to a
unique period of Earth history
b. Correlation
- matching rock units; use Index Fossils [these were abundant organisms, with a widespread
geographic distribution and with a narrow stratigraphic range ("short" evolutionary existence)]
c. Interpreting Sedimentary Environments
Paleoecology and Paleoenvironments - certain types of fossils (Facies Fossils) help in
determining the type of ancient environment
Paleogeography - fossils help to determine the ancient distribution of land and sea, paleolatitude,
trend of ancient shorelines, etc.
Paleoclimate - distribution and morphology (form) of fossils often assist in interpreting ancient
climate
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d. Evidence of Evolution
- vertical distribution of fossils help to trace evolutionary changes throughout Earth history
e. Evidence for Plate Tectonics
- distribution of fossils show how fossil assemblages changed as the lithospheric plates moved
C. Stratigraphy
- study of rock layers (Strata)
1. Correlation (matching rock units) is often accomplished by using:
a. Key (Marker) Bed
- distinctive bed which is nearly the same age everywhere; Exs. = volcanic ash, glacial deposits,
limestones
b. Unconformities
- deposits resting on unconformities (erosional surfaces) are of similar age
2. Formation
- fundamental rock unit used in mapping
D. Absolute (Actual) Dating Techniques
- date geologic events in years
- many dating techniques; the most important are:
1. Radioactivity
a. Isotopes
- forms of an element (with the same number of protons), but with different numbers of neutrons
b. Radioactive Decay
- atoms change to another element by releasing subatomic particles and energy; parent isotope
decays to daughter isotope at a constant rate
c. Radiometric Dating
- measure amount of parent materials relative to their daughter products
Half Life - time required for isotope to decay to half its original amount
Common Radiometric Dating Techniques Are:
Carbon-14 Dating - with a half life of 5,730 years, so can be used to date events only as far back
as 75,000 years; used especially in archeology
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Potassium-Argon - with a half life of 1.25 billion years; abundant in micas and feldspars, so is
often used in dating igneous and metamorphic rocks
d. Abbreviations for years before present on radiometric time scale
Kiloannum (plural = Kiloanna; kilo an) = Ka = thousands of years
Megannum (plural = Meganna; mega an) = Ma = millions of years; M.Y. (or m.y.) = millions of
years, without reference to the radioisotopic time scale
Gigannum (plural = Giganna; giga an) = Ga = billions of years
2. Magnetic Stratigraphy
a. the Earth's Magnetic Field is due to motions of the liquid, iron-rich outer core (it behaves
like a bar magnet with a north and south magnetic polarity)
b. Magnetic Reversal - reversal of polarity in the Earth's magnetic field; polarity reversals are
recorded in iron-rich igneous and sedimentary rocks (Normal Interval = polarity same as todays;
Reversed Polarity = polarity opposite to todays)
c. a Paleomagnetic Polarity Time Scale has been constructed based on magnetic reversals and
"tied" to absolute dates
III. Origins of the Universe and Solar System
A. The Universe
1. Age of the Universe
- believed to be from 10 to 20 billion years old (the best current estimates are 13.7 billion years
old)
- time estimates are based primarily upon the "Law of Redshifts" and the evolutionary history of
stars
- cosmological models suggest that there are not several independent forces in the universe (these
are aspects of a single unified force; Grand Unified Theory, or GUTs)
2. The Big Bang
- the theoretical event that created the Universe; it generated the expanding motion that we see
today
a. Subatomic particles that compose atoms began to form as temperature cooled
- radiation was common; universe was composed primarily of hydrogen and helium
b. matter begins to collect and rotate to form Galaxies (galaxies are the fundamental units of the
universe; each galaxy consists of billions of stars)
B. The Solar System
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1. Origin of the Solar System
- the Solar System formed 4.6 billion years ago from a rotating cloud of gas and dust that
collapsed into a disk
- the Sun, planets and other Solar System objects formed within the swirling disc
2. Types of Planets
a. Terrestrial Planets
- primarily formed from rocks
- includes Mercury, Venus, Earth and Mars
b. Jovian Planets
- formed primarily from gases (helium, hydrogen, methane, ammonia)
- includes Jupiter, Saturn, Uranus and Neptune
3. Origin of the Earth
- Earth was initially a homogeneous cloud of gas and dust; it condensed to form protoplanets
- the protoplanets coalesced; radioactivity and gravity heated the center of the Earth and the outer
surface was heated by meteorite impact
- Earth was differentiated into various layers by gravity
4. Origin of the Earth's Moon
- it is believed that the Moon originated by the collision of a Mars-sized body and the youthful
Earth during the early history of the Solar System
- the ejected debris collected in an orbit around the Earth, and coalesced to form the Moon
C. Structure of the Earth
1. Layers of the Earth
a. Crust
- thin, relatively brittle outer shell of the Earth ranging from 7 to 70 kms thick
- consists of relatively low density rocks
b. Mantle
- constitutes about 80% of the Earth's volume
- the mantle is sandwiched between the crust and the core; it extends to a depth of about 2900 km
- the mantle includes a portion of the Lithosphere (brittle material including the crust and upper
mantle; extends to a depth of 100 km), the Asthenosphere (ductile material extending from about
100 to 350 kms) and the Mesosphere (relatively solid, rigid material that extends from 350 to
2900 kms)
c. Core
- composed mostly of an iron-nickel alloy
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- includes the molten outer core and the solid inner core
D. Earth Processes
1. Internal Processes of the Earth
a. Plate Tectonics
- the Earth is divided into about a dozen major lithospheric plates that float upon the
asthenosphere
- plate motions (divergence, convergence, shear) determine many geologic features
b. Earthquakes
- ground displacement associated with the sudden release of built-up stress in the lithosphere
- earthquakes are typically due to plate tectonic activity
c. Volcanism
- melting of rocks underneath the Earth often form many Earth features
- volcanoes are associated with plate tectonic activity
2. Surface Processes
a. Climate
- the "average weather"
- the climate changes due to changes in solar influx, changes in Earth orbit, continental positions
and shifting ocean currents, and the state of the atmosphere
b. Weathering
- physical and chemical decomposition of rock
- weathering is influenced by climate
c. Erosion
- transport of weathered sediment by water, wind, ice and gravity
d. Deposition of Sediments
- results in the formation of many landforms
IV. Minerals and Introduction to Rocks
A. Minerals
- naturally occurring inorganic solids with definite chemical compositions and crystalline
structure
1. Chemical Composition of Minerals
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a. Elements
- fundamental components, cannot be broken down to simpler substances by ordinary chemical
processes
- there are 94 naturally occurring elements
- the 8 most common are Oxygen (O), Silicon (Si), Aluminum (Al), Iron (Fe), Calcium (Ca),
Sodium (Na), Potassium (K) and Magnesium (Mg); comprise 98% of the Earth's Crust
b. Atoms
- fundamental units of elements
Nucleus - positively charged center of mass; includes protons (with mass and a positive charge)
and neutrons (with mass and a neutral charge)
Electrons - with no mass and a negative charge; the number and orientation of electrons
determines chemical behavior
c. Chemical Reactions
- filling of the outer shells of electrons
Ions = charged atoms; atoms with too few or too many electrons; includes cations (positively
charged atoms) and anions (with negative electrical charges)
Ionic Bonding - cations and anions attract one another; Ex. = sodium and chloride join to form
salt
Covalent Bonding - sharing of electrons between atoms; Ex. = carbon atoms in diamond
Metallic Bonding - outer shell electons travel freely from atom to atom; Ex. = many metals
Compound - chemical combination of two or more elements
2. Crystalline Nature of Minerals
a. Crystal Structure
- orderly arrangement of atoms
b. Unit Cell
- smallest repeating group; the shape of the unit cell determines crystal form
c. Crystal Faces
- external manifestations of crystalline structure; there must be space for mineral growth in order
to form good crystal faces
3. Physical Properties of Minerals
- use color, streak, hardness, crystal form, cleavage, fracture, luster, specific gravity, magnetism,
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chemical reactivity, radioactivity, fluorescence, etc. to identify minerals
4. Mineral Classification
a. Based on the dominant anion present in the Mineral
- including silicates, oxides, sulfides, halides, phosphates, carbonates, native elements and
hydroxides
b. Silicate Minerals
- the most abundant chemical group; composed of silicon (Si) and oxygen (O)
- in Silicate Bonding there are four oxygen for each silicon; bond directions require a tetrahedral
arrangement of the atoms; the tetrahedra may be isolated or form single chains, double chains,
sheets, or frameworks
c. Rock-forming Minerals
- common minerals that combine easily to create rocks
c1. Silicates
- constitute about 90% of the Earth's crust
- Include:
Feldspar - a framework silicate found in almost all rock types; constitutes about 50% of the
Earth's crust; includes potassium feldspar and plagioclase feldspar series
Quartz - a very pure framework silicate; common in continental rocks but rare in oceanic and
mantle rocks
Pyroxene - a single-chain silicate common in oceanic and mantle rocks; Ex. = augite
Amphibole - a double-chain silicate common in continental and oceanic rocks; Ex. = hornblende
Mica - sheet silicates; common in continental rocks; Exs. = biotite and muscovite mica
Olivine - formed of isolated tetrahedra; common in oceanic and mantle rocks
Clay Minerals - hydrated aluminosilicates with a sheet structure; often formed from the
weathering of other minerals; clays are very common in sedimentary rocks
Metamorphic Silicate Minerals - Exs. = garnet, chlorite
c2. Nonsilicate Rock-Forming Minerals
Carbonates - with one carbon and three oxygen atoms; Exs. = calcite, dolomite
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Sulfates - with one sulfur and four oxygen; Ex. = gypsum
Sulfides - sulfur combines with some other element (not oxygen); Ex. = pyrite, galena
Halides - one or more metals combine with one or more halogen elements (fluorine, chlorine,
iodine, bromine); Exs. = halite, fluorite
Oxides - one or more metals combine with oxygen; Exs. = magnetite, hematite, corundum
Phosphates - one or more metals combine with a phosphate group (with 1 phosphorous and 4
oxygen atoms; PO4); Ex. = apatite
Native Elements - mineral consists of a single element; gold, silver, copper, sulfur, graphite,
diamond
5. Mineral Economics
a. Ore
- part of a metal-yielding material that can be economically and legally extracted at a given time;
consists of the ore mineral and waste minerals (gangue)
b. Critical and Strategic Minerals
Critical Minerals - necessary to the economy of a country; NO country is self-sufficient in
mineral resources; U. S. must import 50% or more of 38 of its 63 most important nonfuel
minerals
Strategic Minerals - fuel or nonfuel minerals vital to the industry and defense of a country (Exs. =
manganese, cobalt, platinum, chromium); often stockpiled to cushion against supply
interruptions and sharp price increases
c. Mining and Processing Minerals
c1. Types of Mining
Surface Mining - remove soil, subsoil, and other strata (i.e., Overburden), and then extract a
mineral deposit found fairly close to the Earth's surface; usually discard waste material in Spoils
Piles/Tailings; includes Open Pit Mining (dig holes to remove sand and gravel, building stone,
iron, copper, etc.), Dredging (use draglines and chain buckets to scrape up surface deposits
covered with water), and Strip Mining (use bulldozers, power shovels, or stripping wheels to
remove Earth's surface and recover coal, phosphate rock, etc.)
Subsurface Mining - extract a metal ore or fuel resource (Ex. = coal) from a deep underground
deposit
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c2. Smelting
- separate desired mineral from the other elements in an ore mineral
c3. Environmental Effects of Mineral Extraction and Processing
- disturbs land, and produces noise pollution, thermal pollution, and creates health hazards (solid
wastes; with air, water and soil pollution)
- Acid Mine Drainage - occurs when aerobic bacteria produce sulfuric acid from sulfide minerals
in spoils piles
- smelting often results in huge volumes of air pollutants
d. Mineral Resources and Reserves
d1. Identified Resources
- with a known location, quantity, and grade (quality) or have been estimated from direct
geological evidence and measurements
Reserves - resources that have been identified and from which a usable mineral can be extracted
profitably at present prices with current mining technology
d2. Undiscovered Resources
- potential supplies of a particular mineral resource, believed to exist because of geologic
knowledge and theory, but locations, quality and amounts are unknown
d3. Other Resources
- identified and unidentified resources not classified as reserves
d4. Economically Depleted Minerals
- occurs when finding, extracting, transporting and processing cost more than results are worth
- after depletion must recycle or reuse existing supplies, waste or use less, find a substitute, or do
without
Depletion Time - the time it takes to use a certain portion (usually 80%) of reserves of a mineral
at a given rate of use
B. Rocks and Their Economic Products
Rocks - naturally-formed substance composed of minerals or mineraloids (mineraloids have a
fixed composition but no crystalline structure)
1. Igneous Rocks
- crystallize directly from molten rock (magma)
- includes rocks that crystallize underground (intrusive igneous rocks) and those that crystallize
from lava (extrusive igneous rocks)
- igneous rocks are the main source of many nonfuel minerals
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2. Sedimentary Rocks
- rocks formed as products of decomposition (sediments), rocks formed by chemical
precipitation, or rocks formed from or by organisms
- shale, sandstone and limestone are the most common sedimentary rocks
- economic products include coal, salt, sandstones, gravel, and limestones
3. Metamorphic Rocks
- rocks formed from other rocks due to changes in temperature, pressure, and reaction with
chemical fluids
- include resources such as anthracite coal, slate, marble; also rocks containing talc, asbestos,
graphite
C. Rock Cycle
- all rocks are continually subject to change and can be transformed into other rocks through
geologic processes
V. Igneous Rocks and Igneous Processes
Igneous Rocks - crystallize directly from magma; are the most abundant rocks within the Earth
(include about 95% of all rocks)
A. Magma
- molten rock, often found within a reservoir (magma chamber)
1. The melting of rocks to form magmas is due to:
a. Radioactive isotopes (Uranium, Thorium, Potassium-40) decay and liberate heat
b. Decompression
- pressure acts the opposite of temperature (pressure inhibits melting; the higher the pressure the
greater the temperature required for melting); but place high-pressure rocks under lower pressure
and the melting capability is enhanced
c. Movement of rock masses into high temperature/pressure zones
d. Transfer heat upward from the deep crust or mantle
Convective overturn of a portion of the mantle
Volatile Streaming - Streaming of hot liquids and gases up surfaces of deep fractures
e. Fluxes
- the presence of fluids, especially water, assists in melting rocks
- the presence of water lowers the melting point of magma
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- water tends to "boil off" at lower pressures and causes crystallization of magma below the
surface (basalt is less affected because it has a low water content)
2. Magma-forming Environments
a. Plate Tectonic Subduction Zones
- where oceanic plates "dive" beneath continental or other oceanic plates it causes rocks to melt
due to frictional heating of the plate, pressure release, or addition of water to the subducted plate
- subduction usually results in the formation of intermediate (andesite, diorite) magmas
b. Rift Zones
- magma forms at midoceanic ridges due to seafloor spreading
- basalt magmas dominate
c. Hot Spots
- isolated areas of active volcanism due to presence of hot "mantle plumes"
- often creates a line of volcanoes upon a moving plate
3. Characteristics of Magmas
a. Temperature Range
- basalt melts at 1100-1400°C; granite at 700-900°C
- melting temperature depends upon chemical composition, depth, pressure, and the amount of
water present
b. Composition
- often with oxygen, silica, aluminum, iron, calcium, sodium, potassium, magnesium, and
titanium in variable proportions, depending upon the rock type
Parent Magmas - most important magmas that form igneous rocks; include magma of basalt and
granite composition
c. Magma Density
- expansion of melted magma creates less density and therefore magma tends to rise
- magmas also move toward regions of reduced pressure
B. Formation of Magma
1. Partial Melting
- magmas melt "in sequence" because melting points of minerals differ
2. Magma Composition and Fractionation
a. Bowen's Reaction Series
- crystallization sequence of minerals in an igneous melt
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- minerals that form at the same temperature in the Bowen's Reaction Series are found together in
igneous rocks
b. Crystal Fractionation
- early-formed crystals are removed from the remaining magma and are prevented from reacting
with it
- crystal fractionation is the most important way in which igneous magma composition can be
changed
C. Classifying and Naming Igneous Rocks
- igneous rocks are named on the basis of composition and texture
1. Composition
a. Sialic/Felsic Igneous Rocks
- rocks rich in silica and aluminum
- sialic magmas have higher viscosity (they resists flow); this causes greater explosiveness
- usually continental crust origin; Exs. = granite, rhyolite
b. Mafic Igneous Rocks
- rich in iron and magnesium; mafic (silica-poor) magma has lower viscosity and less explosive
eruptions; usually oceanic crust origin; Exs. = basalt, gabbro
c. Igneous Rocks of Intermediate Composition
- formed from magmas with intermediate chemical composition between felsic and mafic; often
found near island arcs and continental margins; Exs. = andesite, diorite
d. Ultramafic Igneous Rocks
- characteristic of mantle rocks; Ex. = peridotite
2. Texture
- size, shape and arrangement of igneous particles
- often depends on the cooling rate of magma
a. Extrusive Igneous Rocks
- with rapid cooling and quick solidification of magma
a1. Glassy Textures
- no crystals are present because of very rapid cooling; Ex. = obsidian
a2. Aphanitic
- crystals form but are microscopic size; Ex. = basalt, andesite, rhyolite
Rhyolite - felsic glassy to aphanitic igneous rock; volcanoes often form explosive eruptions and
with abundant pyroclastic debris thrown from volcanoes; rhyolite porphyries often have quartz or
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potassium feldspar phenocrysts
Andesite - gray to grayish green extrusive igneous rock of intermedite compositon; named for the
Andes Mountains; commonly formed along Island Arcs and continental margins; forms the
tallest volcanoes in the World
Basalt - mafic aphanitic igneous rock; with approximately 50% silica and 1-2% water; most
common extrusive igneous rock and forms the ocean crust; fluid eruptions with few explosions
a3. Porphyritic
- with at least two sizes of crystals representing multiple cooling histories
- phenocrysts (larger crystals, slower cooling) are embedded in a finer-grained groundmass
(smaller crystals, representing faster cooling)
- Examples = Rhyolite Porphyry, Andesite Porphyry, Basalt Porphyry
b. Plutonic/Intrusive Igneous Rocks
- solidify underground and therefore with slower cooling and larger crystals
b1. Phaneritic
- with larger crystals; Exs. = granite, diorite, gabbro, peridotite
Granite - felsic phaneritic igneous rock; with about 70% silica and 10-15% water; most common
intrusive igneous rock; composition of the continental crust
Diorite - coarse-grained intrusive igneous rock that is intermediate in composition between
granite and gabbro; represents andesite magma chambers
Gabbro - mafic phaneritic igneous rock; least common intrusive rock, often forming in the deep
ocean crust
Peridotite - coarse-grained intrusive igneous rock consisting of olivine and other ferromagnesian
minerals (ultramafic composition); common in the Earth's mantle
b2. Pegmatite
- felsic plutonic igneous rock with extremely large crystals due to the presence of magmatic
water
D. Plutons
- igneous structures formed at depth
- often defined on the basis of morphology and whether the contacts are parallel to the structure
of the adjacent rocks (concordant plutons) or having contacts that cut across or are set an an
angle to the structure of the adjacent rocks (discordant plutons)
1. Types of Plutons
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a. Batholith
- massive, discordant pluton formed from magma that cooled at depth
- often hundreds of square kilometers in area and averages 10 kms thickness
b. Stock
- similar to a batholith but their surface area is less than 100 square kilometers (less than 35
square miles)
- may be a part of a hidden batholith (a cupola)
c. Dike
- a tabular discordant pluton
- forms where magma fills in fractures cutting across rocks; occasionally occurs in groups (dike
swarms)
d. Sill
- tabular concordant pluton
- often formed where more fluid magma (ex. = basalt) is injected between rock layers
e. Laccolith
- concordant, mushroom-shaped concordant pluton that domes the country rock above
- often formed from silica-rich magma
f. Lopolith
- funnel-shaped concordant pluton
- typically formed from mafic magma
2. Textural and Structural Features often associated with Plutons
a. Vesicles
- holes due to escape of gas bubbles
b. Chilled Margins
- finer-grained rocks found at the edges of plutons due to "quenching" of magma
c. Xenoliths
- pieces of host rock in the pluton
d. Contact Metamorphism
- igneous magma "bakes" the surrounding country rock
E. Volcanoes and Volcanic Landforms
1. Lava Structures and Textures
a. Columnar Joints
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- polygonal columns of lava develop in a lava flow due to cooling and fracturing
b. Pahoehoe Lava
- lava flow with a smooth, ropy appearance
- develops where there is fluid basaltic lava
- often develop Lava Tubes/Tunnels (horizontal conduits in the interior of lava flows through
which fluid lavas may flow great distances; if the molten lava continues its forward motion,
cave-like voids are left within the Pahoehoe flows)
c. Aa Lava
- jagged, blocky lava
- develops where there is more viscous lava; often vesicular (with holes)
d. Pillow Lava
- lava flow with bulbous surfaces ("pillows") with a glassy rind
- formed where lava is extruded under water
e. Pyroclastic Rocks
- formed from rock and lava fragments (tephra, pyroclasts) derived from an explosive volcanic
eruption
- fragments classified as ash (less than 2 mm diameter; forms tuffs), cinders (2-64 mm), bombs
(greater than 64 mm, streamlined due to air flow around magma thrown into the air) and blocks
(greater than 64 mm, angular)
- coarser fragments form volcanic breccias (with angular grains) and agglomerates (rounded
grains)
2. Flood Basalts
- deep fractures cause large outpouring of basalt (Fissure Eruptions) and formation of lava
plateaus
- associated with divergent plate tectonic boundaries and "hot spots"
3. Volcanoes and their Associated Features
a. Shield Volcanoes
- volcanoes with low, flat, broad profiles
- formed from low viscosity (basaltic) eruptions; Ex. = Hawaiian Island Volcanoes
b. Cinder Cone
- small volcano made of pyroclastic material; usually basalt to andesite composition
- typically symmetrical profile with a relatively steep (about 30°) slope
- grow rapidly (Ex. = Paricutin Volcano, Mexico)
c. Composite Cones (Stratovolcanoes)
- volcanic cone formed from interlayered lava flows and pyroclastic deposits
- mostly formed from andesite lava and pyroclastics
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 18
- stratovolcanoes are the most dangerous and destructive volcanoes, due to their explosive nature
(which is caused by their viscous silica-rich magmas that resist flow)
- examples include volcanoes of the Cascade Range in the U. S. Pacific Northwest (Mount St.
Helens, Mount Rainier, Mount Hood), as well as Vesuvius in Italy
d. Volcanic Necks and Pipes
- magma in the volcanic conduit crystallizes; softer material forming the slopes of the volcano
then erodes away, leaving a standing Volcanic Neck
- Volcanic Pipe - funnel-shaped tubes (Ex. = Kimberlite Pipes; form at 200 km to 660 km deep
and are the source of diamonds)
e. Calderas
- large, bowl-shaped summit depressions in volcanoes
- may be formed by loss of pyroclastic material within the upper magma chamber and collapse of
the volcano summit (Crater-Lake Type Calderas), by gradual subsidence at the summit as fluid
magma slowly drains out (Hawaiian-Type Calderas) or emplacement of huge volumes of rhyolite
magmas, with subsequent development of ring fractures ejecting viscous gas-rich magmas and
resulting in an extremely large and explosive event (Yellowstone-Type Calderas; these are the
largest volcanic structures on Earth)
f. Ash Flows
- mixtures of gas and fine pyroclastic material flow down the sides of volcanoes
Ignimbrites (Pyroclastic Flows or Nuée Ardentes) - hot (up to 1000°C or more), glowing cloud of
volcanic ash and gas that can rush down slopes of volcanoes at over 100 kms (60 miles) per hour
Ash-flow Tuffs - rocks formed of consolidated volcanic ash from ash flows; intense heating may
form Welded Tuffs
G. Magmas and Ore Deposits
Ore - rock in which a valuable or useful mineral occurs in sufficient concentration to be
economic to mine
1. Magmatic Ore Deposits
a. Crystal settling
- dense crystals in igneous magma sink and form layered deposits; Exs. = chromite and platinum
b. Pegmatite
- a coarse grained igneous rocks formed from the last, water-rich "dregs" of magma
- often contains rare minerals rich in rare earth elements, lithium, boron, beryllium and uranium,
as well as gemstones
2. Hydrothermal Deposits
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 19
a. Source of Water
- water derived from magma, groundwater, and seawater
b. Composition of Hydrothermal Solutions
- consists of hot, salty water forming a powerful solvent
c. Precipitation of Hydrothermal Solutions
- will precipitate due to decrease in temperature, release in pressure and "boiling off" of the
hydrothermal solution, and through chemical reactions
d. Types of Hydrothermal deposits, based on Morphology ("form")
d1. Veins - infilling cracks within rocks
d2. Disseminations - sponge-like openings within rocks are infilled
d3. Blankets - layered hydrothermal deposits, often formed due to "black smokers" at midoceanic ridges
VI. Sedimentary Rocks and Sedimentary Processes
Sedimentary Rocks - rocks formed from the consolidation of loose sediment, by chemical
precipitation, or rocks consisting of the secretions or remains of organisms
- sedimentary rocks comprise only 5% of the total crustal volume, but constitute about 75% of
the rocks found on the continent's surface
- sedimentary rocks are often derived from weathering and erosion processes and therefore often
inherit features of the Earth's "surface system"
- sedimentary rocks accumulate within "sedimentary basins"
A. Sediment
- unconsolidated accumulation of rock and mineral grains and organic matter that has been
transported and deposited by wind, water, or ice
B. Formation of Sedimentary Rocks
1. Types of Sedimentary Rocks
a. Clastic/Detrital Sedimentary Rocks
- form by weathering and erosion of preexisting rocks
- classified on the basis of grain size into mudstones/shales, siltstones, sandstones and
breccias/conglomerates
b. Chemical Sedimentary Rocks
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 20
- form by Inorganic Precipitation of Minerals
- chemical sediments form evaporite minerals such as halite and gypsum
c. Biogenic Sedimentary Rocks
Organic Precipitation of Minerals - sediments precipitated biochemically by organisms; form
many limestones and cherts
Conversion of Organic Matter to Rock - forms coal deposits
2. Erosion and Transport of Sediment
a. Sediment is eroded and transported primarily by water
- also by wind and glacial ice
b. Grain Modification resulting from Transport
Rounding - removal of the corners of grains, often by tumble transport
Sorting - separation of minerals in a sediment by grain size; usually more transport results in
better sorting of the sediment
Maturity - sequential series of changes that occurs during the transport of sediment; Texturally
Mature sediment loses clay and becomes better sorted and more rounded with more transport;
Chemically/Mineralogically Mature sediment loses unstable mineral components and becomes
more quartz-rich
c. Deposition of Sediment
- occurs due to loss of transport energy or loss of solvent
Depositional Environment - site of sediment deposition
d. Lithification of Sediment
- processes which turn sediment to rock
- Processes Include:
Compaction of Sediment - reduces pore space ("holes")
Cementation - precipitate dissolved material in the pore spaces (including silica, calcium
carbonate, and iron oxide)
Crystallization - direct precipitation of crystals; often due to loss of solvent resulting from
evaporation
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 21
C. Sedimentary Structures
- a megascopic multigranular sedimentary feature, usually best studied in outcrops rather than in
hand specimens
1. Primary Sedimentary Structures
-features in sedimentary rocks formed during or shortly after deposition
a. Bedding/Stratification
- sedimentary layering is due to differences in composition, texture, color and cementation
- sedimentary layers are usually deposited horizontally
b. Ripple Marks
- small ridges of sediment resembling a ripple of water and formed on the bedding surface of a
sediment
- include current (asymmetrical) ripples and wave (symmetrical) ripples
c. Cross-stratification/Cross-bedding
- layers within a stratified unit that are oriented at an angle to the dominant stratification
- ripple marks and cross-bedding can be used to determine ancient current direction
d. Graded Bedding
- decreasing particle size from the bottom to the top of a sedimentary layer
- indicate decreasing current velocities
e. Mudcracks
- polygonal cracks formed by shrinkage of fine-grained sediment during dessication
- form where there is alternating wet and dry cycles such as intertidal mudflats along seashores or
desert playa lakes
f. Imprints
- examples include rain drop prints, salt casts, and tracks, trails, and burrows of organisms
g. Fossils
- remains of ancient organisms
2. Secondary (Postdepositional or Chemical) Sedimentary Structures
- form after sediment deposition
a. Nodule = irregular, round, flat structure formed by filling voids in sediment
b. Geodes = hollow, subspherical structures; form around water-filled pocket by crystals
growing inward
c. Concretions = mineral segregations that replace or force aside the surrounding sediment
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 22
D. Sedimentary Processes that form Ore Deposits
1. Precipitation
a. Biogenic Precipitation - due to the action of organisms
Banded Iron Formations (BIFs) - 2.6 to 1.6 Ga year-old layered iron oxides and silicates;
probably formed due to bacteriogenic activity; BIFs are the major source of iron ore
Phosphorites - consists of marine animal debris; important sources of fertilizer
b. Evaporites
- form from the complete evaporation of a solvent
Freshwater Evaporites are often formed in temporary desert lakes (playas); include borax, sodium
sulfate and sodium carbonate; are very important in the chemical industry
Marine Evaporites form in shallow, restricted seas; include halite (salt) and gypsum (gypsum is
used for building materials)
2. Placers
- accumulation of sediment formed by mechanical concentration of heavy mineral particles by
currents (typically streams or waves); placers are sources of gold, tin, platinum, diamonds and
other valuable minerals
3. Fossil Fuels
- remains of plants and animals trapped in sediment that can be used for fuel
a. Requirements for Formation of Fossil Fuels
a1. Photosynthesis and/or Chemosynthesis
- photosynthesis converts solar energy to chemical energy
- chemosynthesis converts carbon molecules and nutrients into energy
a2. Burial
- protect hydrocarbons from chemical degradation
- normally growth processes and decay processes are balanced but in order for hydrocarbons to
accumulate there is burial of organics that prevents decay
b. Types of Hydrocarbons
b1. Petroleum (Crude Oil)
- gooey liquid consisting of hydrocarbon compounds and small amounts of compounds
containing oxygen, sulfur and nitrogen
- oil is relatively cheap, easily transported, with high net energy yield but may be depleted within
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 23
50 years, releases greenhouse gases and other pollutants (the Greenhouse Effect is an increase in
atmospheric temperature caused by the presence of infrared-absorbing gases)
- 12 countries forming the Organization of Petroleum Exporting Countries (OPEC) with
approximately 60% of oil reserves (Saudi Arabia has about 18%)
- the U. S. has about 1.5% of the total World oil reserves (about 21 billion barrels - Canada has
reserves of 179 billion barrels!); the United States uses about 22% of the World's oil (we use
about 69% of our oil for transportation); U. S. imports about 40% of its oil
b1a. Pools - accumulation of oil or gas
b1b. Field - group of pools of a similar geologic type
b1c. Accumulation of Oil
Source Rock - hydrocarbon source rocks often consist of marine shale or limestone deposited
under anoxic (oxygen-poor) conditions
Migration and Maturation - heat and compaction drives oil from the source rock
Reservoir Rock - porous and permeable rock that stores hydrocarbons
Trap - a mass of porous, permeable rock which is sealed on the top and down the sides by
relatively nonporous and impermeable rock; includes structural traps (folds and faults) and
stratigraphic traps (formed from a change in the character of a reservoir rock)
b1d. The Texas Oil Industry
- oil found in many ages of reservoirs, with trapping mechanisms controlled by regional tectonics
and sedimentogical history
Gulf Coast and East Texas - with giant oil fields; especially associated with salt domes and basin
faults; South Texas has many "shoestring sands" containing hydrocarbons
West-Central Texas and North Texas - oil fields are typically small, and are associated with
regional flexures of strata, ancient reefs, and minor fault traps; however, the Barnett Shale
represents one of the largest onshore gas fields in the United States (it covers 5,000 square miles
and may contain as much as 30 trillion cubic feet of natural gas!)
Panhandle - with deeply buried gas fields
West Texas (Permian Basin, Delaware Basin) - huge oil fields with hydrocarbons trapped within
folded rocks, ancient reefs, and lenticular sands
b2. Oil Shale
- fine-grained rock containing Kerogen (a solid, waxy mixture of hydrocarbon compounds)
- if heated to a high temperatures kerogen can be converted into a vapor that can be condensed to
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 24
form a slow-flowing heavy oil (Shale Oil)
- U. S. has large reserves of Oil Shale but it is expensive, requires large amounts of energy and
water to process, causes pollution, and mining disturbs the land surface
b3. Tar Sand
- mixture of clay, sand, water and tarlike heavy oil (Bitumen)
- Bitumen can be extracted from tar sand by heating, then purified and upgraded to synthetic
crude oil
- requires large amounts of water and energy to process, causes pollution, and mining disturbs
land surface
b4. Natural Gas
- underground deposits of gases consisting of 50% to 90% by weight methane gas and small
amounts of heavier gaseous hydrocarbon compounds such as propane and butane
- is cheaper and with more reserves than oil, cleaner and more efficient burning but must be
converted to highly explosive Liquified Natural Gas (LNG) for effective transport overseas and
contains greenhouse gases (greenhouse gases cause "global warming")
b5. Gas Hydrates (Clathrates)
- icelike compounds composed of water and natural gas (typically methane)
- the solid gas hydrates are typically formed within low-temperature deep ocean sediments
- there may be as many as 20 quadrillion cubic meters (700 quadrillion cubic feet) of gas hydrates
in oceanic sediments (this is double the amount of hydrocarbons in the Earth's coal, oil and
natural gas deposits combined)
- however, there is currently no commercial mining of gas hydrates
b6. Coal
- solid, combustible mixture of organic compounds with 30% to 98% carbon by weight, mixed
with varying amounts of water and small amounts of sulfur and nitrogen compounds
- coal is formed from the buried remains of plants (most coal plants lived in swampy areas
associated with ancient deltas)
- ancient plants were subjected to heat and pressure over millions of years; increasing grade of
coal includes lignite, bituminous, and anthracite coal
- coal supplies about 40% of the World's electricity
- can be converted into gaseous or liquid Synfuels (Coal Gasification converts solid coal into
synthetic natural gas, or SNG; Coal Liquefaction converts coal into liquid fuel such as methanol
or synthetic gasoline)
- most abundant fossil fuel but with bad environmental (strip mining, acid rain, etc.) and health
effects (Ex. = Black Lung Disease)
VII. Metamorphic Rocks and Metamorphic Processes
Metamorphic Rocks - rocks derived from pre-existing rocks that changed form in response to
changes in temperature, pressure and the chemical environment
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 25
- metamorphism involves "solid state reactions" (chemical reactions in which melting has not
taken place)
A. Types of Changes due to Metamorphism
1. Textural Changes
- metamorphism causes crystals to recrystallize
- with increased metamorphism the crystals often increase size, the grains rearrange, and grain
boundaries may "suture" together
2. Mineralogical Changes
- the original rock becomes composed of new minerals through solid state transformation
3. Metamorphic Grade
- intensity of metamorphism
- depends upon the amount of temperature, pressure and time
B. Factors that Cause and Influence Metamorphism
1. Temperature
- is especially important for determining composition of metamorphic rocks
Geothermal Gradient - the rate of increase in temperature with depth in the Earth
2. Pressure
a. Lithostatic Pressure
- rock pressure; confining pressure makes particles become more compact but often causes grain
size to increase
b. Directed Pressure
- deformation and shear pressures often cause foliation (a parallel alignment of linear or planar
minerals or with compositional banding) and folding
3. Metasomatism
- introduction of ions in solution into a rock, and the resulting alteration of that rock
- types of metasomatic fluids include:
a. Water
- speeds chemical reactions
b. Carbon Dioxide
- common fluid in high pressure environments
- often leads to changes in composition and reacts with surrounding "country rocks"
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 26
C. Types of Metamorphism
1. Contact (Thermal) Metamorphism
- alteration of rocks at or near contact with igneous pluton
- temperatures at 300-800°C and pressures at 100-3000 atmospheres
a. Type of reaction depends on:
- 1) temperature 2) composition of the intruding mass 3) properties of country rock
b. Contact Aureole
- area affected by metamorphism
- seldom exceeds a few hundred meters in thickness
c. Contactites
- rocks formed due to contact metamorphism
- includes hornfels, some quartzite, some marble and pyrometasomatic ore deposits (with clusters
and veins of gold, sphalerite, galena, pyrite and chalcopyrite)
2. Regional Metamorphism
- developed over extensive areas and most often related to Orogenies (mountain-building events)
- caused by combination of heat, lithostatic and directed pressures and chemically active fluids
a. Regional Metamorphic Zones
- indicate ancient metamorphic conditions on the basis of the first appearance of Index Minerals;
high grade metamorphism occurs nearest the zone of tectonic activity
b. Regional Metamorphic Zones and Index minerals
ZONE
Increasing
Metamorphism
|
|
|
|
|
|
|
\/
Chlorite
Biotite
Garnet
Staurolite
Kyanite
Sillimanite
GRADE OF METAMORPHISM
Low
Low
Middle
Middle
Middle
High
From This Data You Can Draw A Map to Show the Character of Metamorphism
Isograds - boundary between mineral zones; named after the mineral on the high grade side
- the metamorphic zone system has drawbacks because it is restricted to rocks formed from clay
c. Metamorphic Facies
- includes all rocks metamorphosed at the same temperature and pressures
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 27
Types of Metamorphic Facies Include:
Burial Metamorphic Facies - Zeolite Facies
Regional Metamorphic Facies - Greenschist, Blueschist, Amphibolite, Granulite Facies
Contact Metamorphic Facies - Hornfels, Sanidinite Facies
d. Rock type versus metamorphism
With increased metamorphism shale changes to: Slate -> Phyllite -> Schist -> Gneiss ->
Migmatite (a rock that is intermediate between metamorphic and igneous) -> Granite
3. Regional Burial Metamorphism
- with lithostatic pressure but very little heat
- increases with depth and density of the rock
- not much change in texture but forms wierd minerals
4. Cataclastic metamorphism
- crushing and grinding along fracture zones or faults in rocks
- metamorphism rapidly decreases away from the zone of crushing and grinding
a. Products of Cataclastic Metamorphism
Gouge - powdered rock
Cataclasites - rocks formed due to cataclastic metamorphism; includes some breccias
5. Metasomatism
- metamorphic change due to the presence of hot water vapor or other fluids
- may be important in forming certain ore deposits ("Skarns")
6. Impact metamorphism
- due to bolide (meteorite, asteroid, comet) collisions
- common on terrestrial planets and moons (satellites) within the Solar System
VIII. Continental Drift and Plate Tectonics
A. Continental Drift
1. Alfred Wegener
- German meteorologist and polar explorer (1880-1930)
- set forth Continental Drift theory in 1912, and published "The Origin of Continents and
Oceans" in 1915 (which outlined the evidence for Continental Drift)
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 28
2. Wegener's Evidence Included:
a. Fit of Continents
- continental coastlines form a puzzle-like fit (later geoscientists found that the edges of
continental shelves form an even better fit)
- Wegener believed that all continents were once joined into a single huge supercontinent
(Pangaea) surrounded by a World ocean (Panthalassa)
- Pangaea broke apart into a northern continent (Laurasia) and southern continent (Gondwana)
b. Fossil Evidence
- distribution of the fossil plant Glossopteris and the reptile Mesosaurus on the Gondwana
continents indicates that they were once joined
c. Paleoclimatology
- distribution of glacial deposits (tillites), ancient deserts and reefs, and coal deposits indicate the
continents were once joined and were at different paleolatitudes
d. Geologic Evidence
- matching of different rock types indicate that the continents were once joined
3. The Demise of Continental Drift Theory
- Wegener believed that the continents were like "boats" (plowing through the ocean basins) or
"sleds" (sliding on top of oceanic rocks), with the continental crust moving upon the mantle
- there is no evidence that the continents moved through or over the ocean basins; the crust and
uppermost mantle are joined together as a rigid unit
B. Earth and Rock Magnetism
- the Earth is analogous to a bar magnet, with a "north" and "south" magnetic pole
- Earth magnetism is believed to be due to movement in the Earth's core
1. Types of Rock Magnetism
Paleomagnetism - ancient magnetism preserved in rocks
a. Thermoremanent Magnetism
- when an iron-rich rock cools below the Curie Point (about 500°C) it records the magnetic field
orientation
b. Depositional Remanent Magnetism
- when a magnetic grain settles in water, it orients toward the magnetic poles
2. Aspects of Rock Magnetism
a. Declination
- the angle between "True North" and "Magnetic North"
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 29
- this angle changes slightly through time
b. Magnetic Strength
- Earth magnetism changes slightly in intensity through time
c. Magnetic Polarity
- the Earth's magnetic polarity "flips" through time
Normal Magnetic Polarity - the same as today's polarity
Reversed Magnetic Polarity - opposite today's polarity
d. Seafloor Spreading
- the process through which plates diverge and new lithosphere is created at midoceanic ridges
- the youngest rocks are nearest to the midoceanic ridges
- during seafloor spreading the polarity of the Earth's magnetic field alternates, which is
preserved as bands of normal and reversed polarity "stripes" in the magnetized basaltic crust
C. Plate Tectonics
- the theory that the Earth is divided into a series of rigid lithospheric plates that can move over
the Earth's surface
1. Types of lithospheric plates
a. Oceanic (Simatic) Plates
- formed from basalt being produced along Rift Zones at mid-oceanic ridges; have high specific
gravity and therefore form basin areas; constitute 71% of the Earth's surface
b. Continental (Sialic) Plates
- granitic composition and form continental areas
2. Forces that Drive Plate Motion
a. Slab Pull
- dense lithospheric "slabs" of oceanic material sink into the asthenosphere, "pulling" the trailing
plate along
b. Ridge Push
- the elevated position of the mid-oceanic ridge causes lithosphere slabs to "slide" down the
flanks of the ridge
c. Slab Suction
- the drag of the subducting slab induces mantle circulation that pulls the subducting and overriding plates toward the trench
3. Types of Plate Boundaries
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 30
a. Divergent Plate Boundaries
a1. Oceanic Divergent Boundaries
- new simatic oceanic plate material is produced at mid-oceanic ridges through seafloor
spreading
- rates of seafloor spreading average 2-9 centimeters per year as indicated by measurements from
satellites and "laser ranging"
- mid-oceanic ridges constitute a continuous mountain chain that encircles the globe
(approximately 80,000 km long, 1500 km wide, and rises 3 km above the abyssal seafloor); at the
top of mid-oceanic ridges there is a rift valley 1 to 2 km deep
- Ocean floor consists of the following layers (from top to bottom):
1. Pelagic Sediments formed from settling of silica-rich shells, clay, dust and volcanic ash
2. 1.5 km-thick pillow basalts overlying 5-7 km-thick basaltic dikes
3. Gabbros, representing the depleted simatic magma chambers
4. Peridotite (representing the upper mantle)
- the age of the ocean floor is determined by radiometric dating of basalt, study of microfossils,
and correlation of magnetic "stripes"; the oldest ocean rocks are about 200 million years old
a2. Continental Divergent Boundaries
- continental "breakup" (rifting) produces rift valleys
- rifting produces basalt and igneous rocks of mixed composition; weathering of continental
granitic rocks produces feldspar-rich sandstones
- continued continental divergence often creates a passive continental margin (with wide
continental shelves upon which wedges of land-derived terrigenous sediments are deposited and
carbonate platforms build)
- ancient movement of continents is determined by Polar Wandering Curves (curves which map
the past magnetic pole positions relative to a given region or continent)
b. Convergent Plate Boundaries
- these are tectonically active boundaries, typically with relatively narrow continental shelves
b1. Ocean-Ocean Convergent Boundaries
- produces island arc systems (Exs. = Aleutian Islands; Japan) through subduction (oceanic plate
"dives" beneath another oceanic plate)
- island arc systems are typically andesite-rich
Deep-Ocean Trench - a narrow, elongate depression on the seafloor; trenches are formed by
lithospheric plates subducting into the mantle; in the Pacific Ocean many exceed 10,000 meters
(33,000) feet in depth
b2. Ocean-Continent Convergent Boundaries
- produces magmatic arcs (Ex. = Andes Mountains) by oceanic plate subduction beneath
continental plates
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 31
- island and magmatic arcs are areas where oceanic lithospheric plates are being recycled through
subduction
- Benioff Zones are regions of deep-seated earthquakes that represent the plate subduction zone;
denser, older plate material produces steeper subduction zones versus younger "lighter" plates
b3. Continent-Continent Convergent Boundaries
- often produces fold mountain belts (Ex. = Himalyas) through suturing of granitic continental
plates
c. Transform Plate Boundaries
- shear boundaries in which plates slide past one another (Ex. = San Andreas Fault, California)
- transform faults offset mid-oceanic ridges at perpendicular angles; they develop due to different
rates of seafloor spreading and due to the fracturing of a round object (the Earth's surface)
d. Hot Spots and Mantle Plumes
- chains of seamounts and volcanic islands are often formed by lithospheric plates moving over
"fixed" mantle plumes or hot spots
- "weight" of the islands causes isostatic sinking and the formation of flat-topped guyots and
coral atolls
- hot spots may show the direction of plate movement (Example = Hawaiian Islands)
e. Microcontinents
- small pieces of continental crust that have fragmented and moved by sea-floor spreading
- a modern example is the island of Madagascar, located east of Africa
f. Exotic Terranes
- microcontinents that collide and become attached to larger continental margins (Ex.= parts of
Western North America and Appalachia)
IX. Mountain Building and Geologic Structures
A. Mountain Ranges
- linear sets of mountains related by position, direction, age and geologic structure
- mountain ranges are created by linear forces, typically associated with plate tectonic margins
Orogeny - tectonic, plutonic and metamorphic processes involved in mountain building
1. Tectonic Activity associated with Mountain Building
a. Folding and Faulting
- results in rock deformation
b. Volcanic and Plutonic Activity
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 32
c. Earthquakes
d. Metamorphism
2. Types of Plate Boundaries
- different plate boundaries produce different types of mountains
a. Divergent Plate Boundaries
- tensional activity creates horsts (fault blocks uplifted relative to those on either side) and
grabens (fault blocks dropped relative to the adjacent blocks)
- fault block mountains typically rise sharply from the surrounding terrain; include the Sierra
Nevada of California and the Grand Tetons of Wyoming
b. Transform Plate Boundaries
- shear faults often creates "slivers" of mountain ranges
c. Convergent Plate Boundaries
- the most important orogenic areas are associated with convergent plate boundaries
- form several types of distinctive mountain ranges, depending upon the type of plate
convergence
c1. Island Arc Settings
- curved island chains are created through subduction of oceanic plates (Ex. = Japan-Type
Margins)
- subduction leads to the development of forearc basins; with andesite volcanoes and diorite
intrusions
c2. Magmatic Arcs
- subduction of oceanic plates beneath continental plates leads to the development of extensive
plutons and andesitic volcanism, formation of backarc basins, and with extensive thrust faulting
(Ex. = Andean-Type Margins)
c3. Continental Collision
- convergence and collision of continental plates with sequence of 1)volcanic activity 2)collision
and underthrusting of plates and 3)continental suturing (the continental plates "weld" together;
Ex. = Himalaya-Type Margins)
B. Stress and Strain
Stress - force applied to an object
Strain - deformation due to stress
1. Deformation and Rupture of Rocks
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 33
Tectonic Stress
Strain
Compressive
Elastic - strain is proportional to applied stress;
material returns to original dimensions when stress is
removed
Extensional (Tensional)
Plastic - deformation is not proportional to applied
stress; material stays deformed when stress is removed
Shear
Brittle - material tends to rupture rather than deform
under stress
2. Factors which control strain in different materials
a. Nature of the Material
- brittle materials (granite, gneiss, quartzite, etc.) act differently than plastic materials (shale,
phyllite, schist, etc.)
- cleavage and other textural/structural features of the rocks also influence strain
b. Temperature
- higher temperatures favor plastic behavior
c. Pressure
- high pressures favor plastic behavior
d. Time
- stress over a long time period favors plastic behavior
C. Structural Geology
- the study of features formed due to rock deformation
1. Geological Illustrations
a. Geologic Map
- shows the surface distribution of rocks
b. Geologic Cross Section
- shows the distribution of rocks in vertical section
c. Block Diagram
- a combination of a geologic map and cross section that yields a three-dimensional figure
2. Attitude
- the position of rock layers
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 34
- Attitude is Defined By:
a. Strike
- the direction of a horizontal line in the plane of bedding
b. Dip
- the direction in which the rock layer is tilted down from the horizontal; dip is perpendicular to
the strike; the dip angle consists of the angle between a horizontal plane and the bedding plane
- where a geologic contact (boundary between geologic formations) is crossed by a stream, the
contact forms a V, the apex of which points in the direction of dip; the wider the V's the steeper
the dip (vertical beds have no V's)
- in a sequence of formations, none of which has been overturned, the older beds dip toward the
younger.
3. Folds
- bends or flexures in rocks created by ductile deformation
a. Parts of a Fold
Limbs (Flanks) - opposite sides of a fold
Fold Axis - line that traces the maximum curvature of a folded layer and separates the two limbs
Axial Plane - imaginary plane which connects the fold axes of each rock layer and divides the
folds symmetrically
b. Types of folds
Monocline – a fold which exhibits local steepening of an otherwise uniform dip
Anticline – a fold in which the limbs dip away from one another and away from the fold axis;
the oldest eroded bed is on the inside of the structure
Syncline – a fold in which the limbs dip toward one another and toward the fold axis; the oldest
eroded bed is on the outside of the structure
Structural Dome – an anticline roughly as wide as it is long; dips outward in all directions (the
oldest exposed bed is toward the center of the structure)
Structural Basin – a syncline roughly as wide as it is long; the beds dip toward the central portion
of the structure
Asymmetrical Fold – a fold in which the strata of one fold limb dip more steeply than those of
the other
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 35
Overturned Fold – a fold in which both limbs dip in the same direction (although perhaps not in
the same amount)
Plunging Fold – a fold in which the fold axis is inclined at some angle to the horizontal
Recumbent Fold – a fold in which the axial plane is horizontal
4. Unconformities
Unconformity – a substantial gap in the local rock record, indicating an interval of time during
which rocks either were not deposited or were removed later by erosion
a. Angular Unconformity
- an unconformity in which the older strata dip at an angle different from that of the younger
strata
b. Disconformity
- an unconformity in which the beds on either side of the unconformity are parallel
c. Nonconformity
- an unconformity between profoundly different rocks (sedimentary rocks overlying igneous or
metamorphic rocks)
5. Joints and Faults
a. Joint – a break in rock mass with no relative movement of rock on opposite sides of the
break
b. Fault - a surface of rock rupture where there has been relative movement on opposite sides
of the break
b1. Parts of a Fault
Hanging Wall – the block involved in fault movement that would hang overhead for a person
standing in a tunnel along or across the fault
Footwall – the block involved in fault movement that would be under the feet of a person
standing in a tunnel along or across a fault
b2. Types of Faults
b2a. Dip-Slip Fault – a fault in which displacement is in the direction of the fault's dip; dipslip faults include normal, reverse and thrust faults
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 36
Normal Fault – a fault in which the hanging wall moves down relative to the footwall
Reverse Fault- a fault in which the hanging wall moves up relative to the footwall
Thrust Fault – a "low angle reverse fault", in which the hanging wall moves up relative to the
footwall but the dip is gentler (usually less than 20°) than that seen in a reverse fault
NOTE: If you "straddle" a dip-slip fault trace, the foot standing on the oldest bed will also be
standing on the "upthrown" fault block
b2b. Strike-Slip Faults - faults with movement parallel to strike
Right Lateral Strike Slip Fault – a strike-slip fault in which the apparent movement of the
opposite block from where you are standing is to the right
Left Lateral Strike Slip Fault – the opposite block has an apparent offset to the left
X. Earthquakes and the Earth's Interior
Earthquake – a perceptible trembling to violent shaking of the ground produced by the sudden
displacement of rocks below the Earth's surface
A. Seismology
- the study of earthquakes
B. Effects of Earthquakes
1. Fire
- in many earthquakes the most damage is caused by fire
2. Movement may damage human-built structures
3. Destruction by Tsunamis (Seismic Sea Waves)
- a tsunami is a large ocean wave generated at the time of a volcanic eruption or earthquake,
which may cause tremendous destruction and death (the 2004 Indonesian tsunami killed more
than 230,000!)
4. Landslides caused by earthquakes
C. Interpreting Earthquakes
- locate them and determine their strength
1. Locating Earthquakes
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 37
a. Earthquake Focus
- the source of a given set of earthquake waves
b. Earthquake Epicenter
- the area on the Earth's surface directly above the focus of an earthquake
2. Earthquake strength
a. Earthquake intensity
- measure of the extent to which human-built structures are damaged
- intensity is measured by the Mercalli Scale
b. Earthquake magnitude
- measure of the total energy released by an earthquake
- earthquake magnitude is described according to the Richter Magnitude Scale
- Each earthquake number represents approximately ten times more amplitude than the
preceeding number and a 32-fold increase in energy!
c. Recording earthquakes
Seismograph - instrument for recording earthquake vibrations
- earthquake position is calculated by means of Time-Distance Graphs
D. Earth Waves
1. Body Waves
- transmit energy through the earth
a. P (Primary) Waves
- earthquake body waves that travel fastest, moving the particles forward and backward
b. S (Shear) Wave
- earthquake wave that advances by shearing displacement of the rock
2. Surface Waves
- earthquake waves that travel along the surface
a. Love Waves
- transverse surface waves that move from side-to-side
b. Rayleigh Waves
- earthquake waves that roll across the ground like a water wave rolls across the ocean or lake
- most of the shaking felt by earthquake waves is from Rayleigh Waves
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 38
E. Earth Structure
1. Shadow zones
a. P-wave Shadow Zone
- a zone between approximately 105° and 140° from the earthquake epicenter in which P waves
do not appear
b. S-Wave Shadow Zone
- a zone between approximately 105° and 180° from the earthquake epicenter in which S waves
do not appear
- shadow zones indicate the presence of the Earth’s Core
- the S Wave Shadow Zone indicates the Earth's Core is liquid
2. Earth Discontinuities
a. Gutenberg discontinuity
- the boundary between the Earth’s Core and Mantle (at 2900 kilometers depth)
b. Mohorovicic Discontinuity
- the boundary between the Earth’s Crust and Mantle
- the “Moho” is 6 km beneath the ocean and 30 kilometers beneath continents
XI. Weathering and Soils
A. Weathering
- decomposition and disintegration of rocks and minerals at the Earth's surface by mechanical and
chemical processes
Erosion - removal of weathered rocks and minerals from the place where they formed by moving
water, gravity, wind or glaciers
1. Types of Weathering
a. Mechanical Weathering
- physical degradation of rocks; results in size reduction of particles but no change of chemistry
Frost Wedging - expansion of freezing water in rock fractures; often results in accumulation of
angular debris as Talus Slopes
Salt Cracking - analogous to frost wedging; due to salty groundwater and/or ocean spray plus
evaporation forming crystals, whose expansion during growth breaks rocks
Abrasion - wearing and grinding of rock against rock; examples include rocks in stream beds,
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 39
below glaciers, and rocks sand-blasted by the wind
Organic Activity – examples include "root wedging" of plants growing in rock fractures and
bioturbation (disturbing sediment through the activities of organisms)
Exfoliation - pressure release fracturing due to the removal of "overburden" above igneous
plutons; often form concentric fractured layers (Exfoliation Sheets)
b. Chemical Weathering
- breakdown or decomposition of minerals by chemical reaction with water, with other chemicals
dissolved in water, or with gases in the air
- amount of chemical weathering depends primarily on climate influences including temperature,
amount of water, amount of vegetation, Hydrogen Ion Concentration [pH; acid (1) to basic (14)]
and Oxidation - Reduction potential [Eh; Measure of oxidation (lose electrons, "+" values) or
reducing capability of a solution]
-Type of parent material also affects weathering
Acid Rain - introduction of strong acids into a natural system; includes introduction of sulfur
dioxide (mostly from burning high-sulfur coals) to create sulfuric acid and nitrogen oxides to
form nitric acid
2. Spheroidal Weathering
- a weathering process that produces a spherical shape from blocky-shaped parent material
- chemical weathering along fractures causes the corners and edges of angular blocks to weather
faster (because of their greater surface area)
B. Soil
- a surface accumulation of weathered rock and organic matter
- soil is also defined as material capable of supporting plant growth
1. Soil Components
a. Mineral Grains
- soil typically consists of sand to clay size grains
Loam - mixture of sand, clay, and organic matter
b. Organic Material
Litter - organic matter on the surface
Humus - decomposed organic matter in the soil
2. Soil Profiles
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 40
O Horizon - topmost layer, usually dark; the O Horizon is a mixture of humus and litter
A Horizon - often combined with the O Horizon in classifications (this is termed "Topsoil"); the
A Horizon consists of a mixture of humus and minerals and contains a high density of organisms;
it is also termed the Zone of Leaching (rain and organic acids leach ions and clay and nutrients
are removed)
B Horizon – the Zone of Accumulation, where clay is entrapped and ions are precipitated
C Horizon - unweathered to slightly weathered rock representing the “parent material” of the
soil
R Horizon – zone of partially-weathered bedrock below the soil horizons
3. Factors that Influence Soil Formation
a. Type of Parent Rock
- influence the type of materials present, amount of fractures, and permeability (ability of fluids
to flow through the system)
- granite often produces sand-rich soils; basalts often produce clay-rich soils
b. Time
- as time progresses and with more weathering soils often become more alike
c. Climate
- affects precipitation and vegetation, which greatly influences soil characteristics
Pedalfers - often develop in moderate climates; with bidirectional movement of ions; pedalfers
often have "hardpans" at the top of the B Horizon
Pedocals - form in arid climates; with upward movement of ions to form Caliche (calcium
carbonate) or Silcrete (silica) Duricrusts on the surface
Laterites - form in humid climates; with downward movement of ions; laterites typically form
nutrient-poor soils
d. Rates of Growth and Decay of Organic Matter
- balanced growth and decay is best for rich soil formation
e. Slope Angle
- best to have minimum erosion so that developing soil will not be removed
4. Soil Problems and Soil Conservation
a. Soil Erosion
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 41
- movement of soil components (especially surface-litter and topsoil) from one place to another,
usually by flowing water or wind (especially in areas where vegetation is lost)
- causes less fertile soil and soil that holds less water
- excessive soil erosion is affecting about 1/3 of the World's croplands (mostly Asia and Africa);
soil erosion is especially due to overgrazing, deforestation, and unsustainable farming methods
Reducing Soil Erosion:
- use Conservation-tillage farming that disturbs soil as little as possible when planting crops
- Terrace steeper slopes, Contour Farm gently sloping land, Strip Crop (plant strips of soil-saving
cover crops between grains, etc.), or utilize Alley Cropping/Agroforestry (plant crop "alleys"
between trees and shrubs), Gully Reclamation (dam and vegetate gullies), and build Windbreaks
b. Misuse of Inorganic Fertilizers
- inorganic fertilizers do not add humus to the soil and may result in pollution (especially cultural
eutrophication)
Maintaining and Restoring Soil Fertility:
- use organic fertilizer [including animal manure, green manure (vegetation plowed into the soil),
or compost (partially decomposed organic plant and animal matter)] or commercial inorganic
fertilizer (mixtures of plant nutrients such as nitrates, phosphates and potassium)
- use Crop Rotation and alternate planting nutrient-depleting plants (Ex. = corn, tobacco, cotton)
with nutrient-restoring plants (Exs. = legumes, oats, barley, rye, or sorghum)
c. Irrigation Misuse
- about 11% of the World's land surface is used to grow crops; about 40% of the World’s food
supply comes from the 2% of land that is irrigated
- improper irrigation leads to accumulation of salts in the soil (Salinization) and raises the water
table to envelop and kill plant roots (Waterlogging)
d. Desertification
- conversion of rangeland, rain-fed cropland or irrigated cropland to desert, with a 10% or more
drop in agricultural productivity
- usually due to combination of overgrazing, soil erosion, prolonged drought, and climate change
XII. Landslides and Mass Wasting
Mass Wasting - movement of earth material downslope, primarily by gravity
A. Agents of Mass Movement
1. Gravity
2. Water
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 42
3. Air
B. Factors that control Mass Wasting
1. Relief (vertical Distance) and Steepness of Slope
2. Type of Rock and Orientation of Rock Layers
a. Shear Strength
- resistance of earth materials to being pulled apart
- massive rock types typically have high sheer strength; loose sediments have low shear strength
b. Rock Orientation
- position and orientation of rocks leads to stable or unstable situations
3. Nature of Unconsolidated Debris
Angle of Repose - maximum stable slope angle (for boulders is about 45°; for sand about 35°)
4. Water and Vegetation
- water adds mass (and therefore with greater influence by gravity)
- small amounts of water increases shear strength of sediment; large amounts lowers shear
strength of sediments
- water acts as a lubricant to ease the movement of sediment
- vegetation anchors sediment and inhibits mass movement
C. Classification of Mass Movements
1. Rapid Movement
a. Slump (Slope Failure)
- downward and outward movement of rock or unconsolidated material traveling as a unit
- occurs where original slope is sharply steepened
b. Rock Slides/Landslides/Rock Avalanches
- sudden, rapid slides of bedrock along planes of weakness
- the rapid movement may be aided by air trapped beneath the debris, and have been known to
reach speeds in excess of 125 miles per hour
c. Mudflows and Debris Flows
- well-mixed mass of rock, earth and water that flows down valley slopes with the consistency of
newly mixed concrete
- mudflows and debris flows are common in arid or semi-arid environments
d. Talus
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 43
- slope built by accumulating rock fragments at the foot of a cliff or ridge
2. Slow Movements
a. Creep
- slow down-slope movement of surface material caused by gravity and moisture
b. Solifluction
- downslope movement of waterlogged sediment over impermeable layers within arctic areas
during the warm season
c. Rock glaciers
- rock and ice mixtures that flow in valleys of mountainous regions
XIII. Streams and Rivers
- fluvial environments
A. The Hydrologic System
- the system of moving water at the Earth's surface
1. Water returns to the atmosphere by:
a. Evaporation
b. Transpiration
- process by which water is released into the atmosphere by plants
2. Water returns to land by means of precipitation
3. Water is temporarily stored:
a. in bodies of water
b. in glaciers
c. as groundwater
4. Runoff
- water that flows over the land surface
B. River System
- consists of a main channel and all of the tributaries that flow into it
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 44
1. Drainage Basin
- total area that contributes water to a single river system
- forms a contributive system of a river (water from tributaries are “contributed” to progressively
larger channels)
- is primarily an area of erosion
2. Divide
- a ridge separating two drainage basins
3. Trunk Stream
- forms the transporting system into which tributaries flow
- is an area of erosion and deposition
4. Distributary System
- network of branching streams into which a river divides where it reaches a delta
- is an area of deposition
C. Flow of water in streams is influenced by:
1. Volume of water
a. Discharge - amount of water passing a given point during a specific interval of time
Perennial Streams - flow continually throughout the year; with substantial input by groundwater
(the amount of groundwater input is termed base flow)
Intermittent (Ephemeral) Streams - stream through which water flows only part of the time
2. Stream Velocity
- depends on the shape and roughness of the channel, the type of stream pattern, the gradient
(vertical drop of stream over a distance; the gradient is steepest at the headwaters and decreases
downslope) and the volume of water
3. Shape and size of channel
- stream channels adjust shapes to minimize resistance to flow
4. Stream Gradient
- slope of the stream bed (in feet per mile or meters per kilometer)
5. Base Level
- lowest level to which a stream can erode its channel
a. Temporary base level
- levels of tributary junctions and lakes
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 45
b. Ultimate base level
- sea level
c. Entrenched Meanders
- rivers confined to a canyon or gorge, with little or no floodplain
- entrenched meanders are formed where base level is rapidly lowered, so that the river begins
downcutting into its channel faster than it can change course
- example = Snake River Canyon, southern Idaho
D. Stream Erosion and Transport
1. Erosion is due to:
a. Abrasion
b. Dissolution
c. Hydraulic action
- currents wash sediments downstream
2. Load
- sedimentary particles carried by wind, water or ice
a. Physical load
- carried particles
a1. Bed load
-carried on bottom
Traction- particles in constant contact with bottom; slide and roll; gravel
Saltation- particles bounce; sand
a2. Suspended load
- particles carried in water column due to turbulent flow; silt and clay
b. Chemical (Dissolved) Load
- dissolved ions carried by stream
3. Headward Erosion
- extension of a stream headward, up the regional slope of erosion
- may lead to Stream Piracy (where there is a diversion of the headwaters of one stream into
another stream; stream piracy occurs by headward erosion of a stream having greater erosive
power than the stream it captures)
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 46
4. Superposed Stream
- a stream that cuts across a ridge lying across its path; this occurs where the stream's course was
established on uniform layers at a higher level, then cuts down through the resistant bedrock
ridge below
5. Stream terrace
- one of a series of level surfaces in a stream valley formed by downcutting or alluviation (i.e.,
sedimentary deposition) due to raising or lowering of base level (stream terraces are therefore
relict features formed when the stream was at a higher elevation)
- may form Paired Terraces (where the terraces are at equal elevations on opposite sides of the
stream) or Unpaired Terraces (where the stream encounters material on one side that resists
erosion, leaving a single terrace with no corresponding terrace on the resistant side)
E. Stream Deposition
- occurs in the lower reaches of stream systems (in areas of lower gradient)
- most features are formed during flood stages
- depositional features include floodplains, point bars, natural levees and deltas
F. Drainage Patterns versus Tectonics
- there is a strong tendency for major river systems to flow from a mountain range across the
continental craton and empty into the sea along the trailing edge of a continent
- variations in drainage patterns may reflect local rifting and subsidence within the continent or
disruptions due to glaciation, development of deserts or volcanism
- streams may be divided into narrow V-shaped valleys with broad divides (Youthful Streams)
and streams with wide valleys and broad floodplains with little or no divides (Mature or Old Age
Streams); the stream type evolves as it cuts its channel closer to base level
G. Types of Rivers and Streams
1. Meandering Streams/Rivers
- a sinuous stream or river created in areas of low gradient and where the stream has substantial
base flow (base flow is the amount of water contributed by springs)
2. Braided stream
- a stream or river with a complex of converging and diverging channels separated by bars or
islands; form where more sediment is available than can be removed by the discharge of the
stream
- typically form in semiarid regions, in mountains, in areas with glacial outwash, or in regions
with monsoonal climates
H. Patterns made by Rivers and Streams
1. Dendritic Pattern
- resembles a branching tree
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 47
- dendritic patterns often form where the underlying bedrock has a uniform resistance to erosion
2. Radial Pattern
- streams radiate out from a high central zone (mountain, volcano, etc.)
3. Rectangular Pattern
- rectangular stream patterns form where the underlying bedrock is crisscrossed with fractures
- it is sometimes developed on tilted, flat, resistant beds (ex.= tilted slate beds)
4. Trellis Pattern
- often develops between elongate folds, with long trunk streams paralleling the folds and short
streams cutting through rocks on the hill sides
5. Distributary Pattern
- streams branch in a downstream direction; develops on deltas and alluvial fans
I. Fluvial Features
1. Flood plain
- the flat, occasionally flooded area bordering a stream
2. Meander
- a broad, looping bend in a river
3. Oxbow lake
- a lake formed in the channel of an abandoned meander
4. Cutbank
- outer bank in the bend of a meandering stream that is the site of maximum erosion
5. Point bar
- a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander bend
6. Natural levee
- a broad, low embankment built up along the banks of a river channel during floods
7. Backswamp
- the marshy area of a flood plain at some distance beyond and lower than the natural levees that
confine the river
J. Deltas
- deposits that form where a stream enters a larger body of water
- deltas are often triangular-shaped due to the outward branching of the main stream into smaller
distributary channels
- during the constructional phase the delta progrades (builds out), deposits sediment around the
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 48
mouth of the channel, and eventually switches distributary channels
- during the destructional, or abandonment, phase the shape of the delta is modified by the action
of waves, tides, and delta subsidence
XIV. Groundwater, Water Resources and Karst
Groundwater - underground water; constitutes about 70 times the amount of water found in rivers
and streams
A. Groundwater potential
- relative ability of rock or sediment to store underground water
- groundwater potential especially depends on porosity (the percentage of open space in a rock or
sediment); sandstones have about 5-20% porosity, with up to 50% in unconsolidated sediment
(there is up to 90% porosity in clay but clay loses porosity quickly with burial)
B. Permeability
- speed of groundwater flow through rock; permeability averages 4 centimeters per day or 15
meters per year
Controls on Permeability Include:
1. Particle Size and Sorting
- smaller particles reduce flow rate
- poorly-sorted sediments have poorer permeability
2. Size of Pores
- increased surface tension in small pores reduces flow rate
3. Porosity
- more holes contain more water; but pore spaces must be connected in order to have good
permeability
4. Structural Features
- fracture patterns and faults in rocks typically increase permeability
C. Vertical Distribution of Groundwater
1. Soil Water Zone (Belt of Soil Moisture)
- Small droplets of water in plant roots
2. Aeration Zone
- below the soil water zone, where the pores are partially filled with "suspended" water
3. Saturation Zone
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 49
- beneath the zone of aeration, where the pores are completely filled with groundwater
D. Water Table
- surface between the Zone of Aeration and the Zone of Saturation
1. Recharge
- addition of water to the groundwater reservoir
- the height of the water table depends on the amount of recharge versus the amount of
groundwater drawn off by plants and humans
2. Aquifer
- permeable material that carries underground water
a. Aquifer Classification Based Upon Bounding Surfaces
Unconfined Aquifer - with a "free water table" at atmospheric pressure
Confined Aquifer – is confined between Aquicludes (impermeable sediment or rock stopping the
flow of groundwater); in a confined aquifer the pressure is greater than atmospheric pressure so if
a well is drilled into a confined aquifer the water rises under its own pressure (this is termed an
Artesian Well)
b. Aquifer Classification based on Local and Regional Geology
- include 1)Artesian Systems 2)Fracture Aquifers 3)Water Table Aquifers (Unconfined
Aquifers) 4)Perched Water Table Aquifers 5)Karst Aquifers
3. Hydraulic Gradient
- the slope of the water table
- the greater the slope of the water table, the greater the water pressure (Hydraulic Head)
4. Cone of Depression
- a conical depression in the water table where groundwater is pumped out at a faster rate than
can be recharged
E. Spring
- surface discharge of groundwater
F. Water Resources and Water Pollution
- only 3% of Earth's water is freshwater, and only about .003% is readily available
Water Stress Indicator - imbalance between water resources and water use
1. Sources of Water
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 50
a. Surface Water
- found in streams, lakes, wetlands and artificial reservoirs
- a Watershed is the land area that delivers surface runoff (water, sediment and dissolved
substances) via small streams to a major stream or river
b. Groundwater
- most groundwater is used for agricultural irrigation (about 4 times more water is used for
irrigation than for public water supply)
- in many areas groundwater is being removed at a much higher rate than can be replaced through
recharge (Ex. = the Ogallala Aquifer on the U. S. High Plains)
- the removal of water from aquifers may also lead to land subsidence
2. Water Resource Problems
a. Drought
- occurs in areas that do not get enough water due to lower than normal precipitation, higher than
normal temperatures (therefore with increased evaporation), or both
- 40% of World population lives in drought-prone areas
- drought effects increased due to population increase, deforestation, desertification, monoculture
(heavy reliance on one type of plant or animal), and politics
b. Floods
- increased rainfall or rapid snow melt causes river waters to overflow their channel and cover the
Floodplain
- floodplains often support high human populations due to rich soils, abundant water, and ease of
irrigation
- floods are more severe where vegetation has been removed and/or where urbanization increases
runoff
- flood risks may be reduced by channelization (straighten channels to increases flow), artificial
levees (build along banks to prevent overflow), flood control dams, or constructing floodfrequency curves (show how often a flood of a certain size should happen in order to plan
development)
c. Desalination
- remove dissolved salts from ocean water or brackish (slightly salty) groundwater
- mostly use distillation (evaporate saltwater by heat and condense it to freshwater; distillation is
very expensive and produces huge amounts of brine) and reverse osmosis (pump saltwater
through a porous membrane that traps salts)
d. Water Pollution
- 1.1 billion people in the World do not have safe drinking water
d1. Major Types of Water Pollutants
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 51
Pathogens - disease-causing bacteria, viruses, protozoa and parasitic worms; a good indicator of
water quality is counting coliform bacteria
Organic Wastes - decomposition by bacteria depletes dissolved oxygen in water (biological
oxygen demand, or BOD, is the amount of oxygen needed for decomposition of organics)
Water-soluble Inorganic Chemicals – include acids, salts and toxic metals (Ex. = lead, mercury)
Inorganic Plant Nutrients - nitrates and phosphates cause algal bloom and eutrophication
Organic Chemicals - petroleum, plastics, pesticides, cleaning solvents, detergents, etc.
Sediment/Suspended Matter - reduces photosynthesis, carries harmful substances, and causes
siltification
Radioactive Isotopes - causes genetic damage, birth defects, and cancer
Heat from Power Plants - lowers oxygen content and harms aquatic life
Alien Species (Genetic Pollution) - outcompete native species
d2. Pollution Sources
Point Source Pollution - discharge pollution from particular sources (discharge from pipes,
ditches or sewers into surface water bodies)
Nonpoint Source Pollution - cannot be traced to any single source; most nonpoint source
pollution is due to agriculture; nonpoint source pollution is the worst water pollution sources
d3. Water Pollution Areas
Stream Pollution - flowing streams usually recover rapidly from pollution through dilution and
bacterial decay
Lake Pollution - dilution is usually less effective due to water stratification; nitrates and
phosphates from agricultural areas and sewers cause cultural eutrophication (algae bloom and
die, using up lake oxygen)
Groundwater Pollution - slow water movement does not dilute pollution and nondegradable
wastes remain there permanently
Ocean Pollution - is worst around coastal areas (wetlands, estuaries, coral reefs, mangrove
swamps) due to large human populations and often "sluggish" water circulation
d4. Water Treatment
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 52
- pure groundwater requires little treatment
- surface water is usually stored in a reservoir for several days (suspended matter settles and
oxygen increases), then the water is passed through sand filters, then through activated charcoal,
and then disinfected
G. Caves
- due to dissolution by underground water
1. Karst topography
- areas underlain by soluble rocks (often carbonate rocks such as limestone or dolomite; can also
be evaporite rocks such as gypsum) which display features created by dissolution
a. Types of Karst Features
Sinkholes - irregular depressions formed by dissolution of underlying carbonate rocks
Dry Valleys - areas that lack surface drainage; streams and rivers are often absent because the
surface water quickly flows underground due to the presence of caverns
Tower Karst - develops in tropical or subtropical regions with thick beds of highly jointed
limestone; groundwater dissolves large amounts of limestone along the joints, leaving the
residual towers (Examples are in southern China and Puerto Rico)
Caves - are also products of karst topography
2. Cave (Cavern)
- an underground chamber or series of chambers formed from the dissolution of rocks (typically
carbonates such as limestone or dolomite, but may also be formed within evaporite rocks such as
gypsum)
a. Dripstone
- features formed from calcium carbonate dripping off cave ceilings and walls
- the collective term for dripstone features in caves are Speleothems
Types of Speleothems:
Stalactites - extend down from cave ceilings
Stalagmites - grow upward and form by calcium carbonate dripping on the floor
Pillars (columns) - form where a stalactite and stalagmite meet
Flowstone (Travertine) - Water dripping down cave walls and across cave floors deposits bands
of calcium carbonate
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 53
G. Geyser
- a type of hot spring that intermittently ejects steam and hot water due to the interaction of
groundwater with an underlying heat source
1. Geyser Deposits
- if the water contains dissolved silica, Siliceous Sinter (Geyserite) may be formed around the hot
spring or geyer
- if the water contains dissolved calcium carbonate, Travertine (layered limestone) or Calcareous
Tufa (porous limestone) may be deposited
2. Geothermal Energy
- geysers (or drilling into hot springs) may be used to drive turbines to produce electricity
- geothermal energy provides about 1/2 of one percent of the World's energy, but is very
important in some regions (such as Iceland); the largest "dry steam" facility in the World is The
Geysers, north of San Francisco, California (here geyser steam is used to directly turn the electric
turbines)
XV. Glaciers and Glaciation
Glacier - system of flowing ice that originates on land through the accumulation and
recrystallization of snow; therefore more snow must fall each year than is lost by melting and
evaporation
A. Formation of Glaciers
1. Stages of ice formation
a. Snow - "powder"; loose material, with high porosity
b. Firn/neve - granular ice
c. Glacial ice - composed of tightly interlocking ice crystals
B. Glacial Erosion
- glacial plucking (quarrying) and abrasion may create:
1. striations
2. rock flour (due to grinding by glaciers)
C. Glacial Zones
1. Zone of Accumulation
- with net gain of ice
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 54
2. Zone of Ablation
- where ice leaves the system by melting and evaporation
D. Movement of Glaciers
1. Zones of movement
a. Fracture (Brittle) Zone
- upper glacial zone (less than 50 meters thick) that breaks sharply rather than flows (often form
crevasses, which are cracks in ice sheets or glaciers)
b. Plastic (Flow) Zone
- lower glacial zone (at greater than 50 meters depth) that behaves plastically due to pressure of
overlying ice
2. Velocity of glaciers depends on:
a. thickness of ice
b. steepness of slope
c. size of cross-sectional area through which ice is moving
3. Classification based on velocity
a. Outlet glacier
- fast-moving valley glacier created by movement of ice sheets through narrow valleys
b. Surging glaciers
- move several kilometers per year due to lubrication by water at the base of the glacier
E. Types of Glaciers
1. Alpine (Valley) Glaciers
- long, narrow rivers of ice that originate in the snowfields of high mountain ranges and flow
down preexisting stream valleys
- size of alpine glaciers depends upon temperature and the amount of precipitation
a. Cirque Glacier
- a very small alpine glacier formed within a cirque
b. Trunk Glacier
- a larger alpine glacier formed when smaller valley glaciers flow into one another
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 55
c. Piedmont Glacier
- a sheet-like glacier that forms where alpine glaciers coalesce at the base of mountains
d. Alpine glacial features
d1. Erosional Features
Cirque - an amphitheater-shaped depression at the head of a glacial valley, excavated mainly by
ice plucking and frost wedging
Tarn – a small mountain lake within a cirque
Paternoster Lakes – a string of lakes formed in the floor of a glacial valley
Arête - a narrow, sharp ridge separating two adjacent glacial valleys
Col – a sharp-edged gap or "pass" formed when cirques join from opposite sides of a ridge
Horn - a sharp peak formed at the intersection of the headwalls of three or more cirques
U-shaped Glacial Valley – the shape of a valley in cross-section due to glacial erosion
Hanging Valley - a tributary valley with the floor lying ("hanging") above the valley floor of the
main stream or shore to which it flows; hanging valleys are commonly created by deepening of
the main valley by glaciation
Fjord - a glaciated valley flooded by the sea to form a long, narrow, steep-walled inlet
d2. Depositional Features
Moraine - a general term for a landform composed of till
Terminal (End) Moraine - a ridge of till that accumulates at the margin of a glacier
Recessional Moraine - a ridge of till deposited at the margin of a glacier during a period of
temporary stability in its general recession
Lateral Moraine - an accumulation of till deposited along the side margins of a valley glacier
Medial Moraine - a ridge of till formed in the middle of a valley glacier by the junction of two
lateral moraines where two valley glaciers converge
Outwash Plain - the area beyond the margins of a glacier where meltwater deposits sand, gravel,
and mud washed out from the glacier
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 56
2. Continental Glacier
- a thick ice sheet covering large parts of a continent (Exs= Greenland, Antarctica)
- Continental Glaciers are often associated with:
a. Icebergs
- floating masses of glacial ice separated and broken away from ice sheets
- Pinnacle Icebergs are typically formed from Alpine Glaciers; Tabular Icebergs are typically
formed from Continental Glaciers
b. Ice shelves
- floating glacial ice attached to ice sheets
- when Ice Shelves break off in the ocean, they may form huge Ice Islands
c. Continental Glacial Features
c1. Erosional Features
Striation - a scratch or groove produced on the surface of a rock by a geologic agent, such as a
glacier or stream
Kettle - a closed depression in a deposit of glacial drift formed where a block of ice was buried or
partly buried and then melted
c2. Depositional Features
Terminal (End) Moraine
Recessional Moraine
Ground Moraine - glacial deposits that cover an area formerly occupied by a glacier; they
typically produce a landscape of low, gently rolling hills
Drumlin - a smooth, glacially streamlined hill that is elongate in the direction of ice movement;
drumlins are usually composed of till
Erratic - a large boulder carried by glacial ice to an area far removed from its point of origin
Esker - a long, narrow, sinuous ridge of stratified glacial drift deposited by a stream flowing
beneath a glacier in a tunnel or in a subglacial stream bed
Kame - a body of stratified glacial sediment; a mound or an irregular ridge deposited by a
subglacial stream as an alluvial fan or a delta
c3. Features formed in Periglacial Areas (Regions in front of Glaciers)
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 57
Outwash Plain - the area beyond the margins of a glacier where meltwater deposits sand, gravel,
and mud washed out from the glacier
Block Field - extensive flat or gently sloping areas covered with large, angular and subangular
blocks formed by frost wedging
Varves - a pair of thin sedimentary layers deposited on a lake bottom during a one year period,
one relatively coarse-grained and light-colored (formed during Spring runoff), and the other
relatively fine-grained and dark-colored (formed during the Winter)
Loess - unconsolidated, wind-deposited silt and dust
F. Major episodes of Glaciation
- in the past great ice sheets have covered large sections of the earth where no ice now exists
(Exs.= PreCambrian, Late Paleozoic and Pleistocene "Ice Ages")
1. Causes of Glaciation
a. Astronomical hypothesis
- variations in solar radiation
- variations in the Earth's orbital path and rotational wobble (these are termed Milankovitch
Cycles)
b. Atmospheric changes due to:
- decrease in carbon dioxide
- increase in volcanic activity
c. Oceanic controls
- ocean current patterns influence weather patterns
d. Plate Tectonics
- movement of continents over polar regions causes buildup of ice
2. Results of Glaciation
a. changes in sea level
- during Ice Ages there are extreme drops in sealevel
b. isostatic adjustment of the crust
- glaciers depress the land surface due to their weight
c. modification of drainage systems
- rivers often change course due to influences by glaciers
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 58
d. creation of numerous lakes
e. selective extinction of many plants and animals
XVI. Deserts
- areas of low precipitation (less than 25 centimeters/ 10 inches per year)
- deserts are characterized by Internal Drainage (where water flows toward the center of the
desert basin, rather than to the sea)
Semiarid area (Steppe) - with 25-50 centimeters per year precipitation (10-20 inches)
A. Types of Deserts
1. Climatic (Tropical) Deserts
- occur in subtropical latitudes (centered at 30° north and south of the Equator)
- formed by atmospheric circulation patterns
2. Topographic (Rain Shadow) Deserts
- deficient in rainfall because they are located in the center of continents or cut off from rainbearing winds by high mountains
3. Coastal Deserts
- areas that are arid because they are located at coastlines bordered by cold, moisture-deficient
currents
B. Desert Landforms
- most desert features are formed by the action of water
- deserts are often associated with Basin-and-Range Topography, with bare rock areas along the
ranges, and with alluvial fans, arroyos, dunes and playas toward the center of the basin
1. Depositional Features
a. Dune
- a low mound of fine-grained material that accumulates as a result of sediment transport in a
current system
Eolian Dunes - sand dunes formed by the wind
Types of Eolian Sand Dunes Include:
Barchan dune - a crescent-shaped dune, the tips or horns of which point downwind; form in
desert areas where sand is scarce
Barchanoid dune - form scalloped rows of sand oriented at right angles to the wind direction
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 59
(they are intermediate beween barchans and transverse dunes)
Transverse dune - an asymmetrical dune ridge that forms at right angles to the direction of
prevailing winds
Seif (Longitudinal) dune - a dune of great height and length oriented in the direction of the
prevailing wind
Parabolic dune - a dune shaped like a parabola with the concave side toward the wind; forms in
sand areas covered with vegetation; deflation creates a "blowout"
Stellate (Star) dune - a mound of sand with a high central point and arms radiating in various
directions
b. Playa
- a depression in the center of a desert basin, the site of occasional temporary lakes
c. Alluvial fan
- a fan-shaped deposit of sediment built by a stream where it emerges from an upland or a
mountain range into a broad valley or plain; alluvial fans are common in arid and semi-arid
climates but are not restricted to them
d. Bajada
- the surface of a system of coalesced alluvial fans
2. Desert Erosion
a. Desert Erosional Processes
- erosional features are more common in deserts than depositional features (the dominant features
of deserts are typically bare-rock surfaces, termed Hamadas)
- wind often removes finer-grained material, leaving coarse pebbles and gravel (Desert
Pavement); this gravel may be faceted and polished by the wind to create Ventifacts
b. Common Erosional Features in Deserts Include:
b1. Stream Features
Arroyo (Wadi) – an intermittent desert stream
b2. Flat-Topped Erosional Topography
Plateau - an extensive, flat upland area
Mesa - a flat-topped, steep-sided highland capped with a resistant rock formation; a mesa is
smaller than a plateau but larger than a butte
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 60
Butte - a somewhat isolated hill, usually capped with a resistant layer of rock and bordered by
talus; a butte is an erosional remnant of a formerly more extensive slope
b3. Yardangs
- streamlined, wind-sculpted ridges that are oriented parallel to the prevailing wind (they often
look like an inverted ship's hull)
b4. Inselbergs
- erosional remnants of mountains in arid regions
- inselbergs are surrounded by pediments and thick basin fills of playa and alluvial fan sediments
b5. Pediments
- a gently sloping erosional surfaces formed at the base of a receeding mountain or cliff
- pediments cut across the bedrock and can be covered with a veneer of sediment
XVII. Shorelines and Coastal Processes
- areas dominated by waves and tides
A. Waves and Tides
1. Waves
- wind-driven wave of water that provides most of the energy to modify shorelines
Nearshore Zones include:
a. Breaker zone
- nearshore zone where wave velocity and wavelength decreases; waves become higher and more
asymmetrical
b. Surf Zone
- nearshore zone where over-steepened waves topple over and crash onto the beach
c. Swash Zone
- thin sheet of water moves up the beach face
d. Backwash Zone
- sheet of water moves down the beach face
2. Tides
- produced by a combination of external forces (primarily the attraction of the Moon and the
centrifugal force of the Earth-Moon system)
- tides affect coasts by initiating a rise and fall in the water level and by generating currents
- tides are most influential in areas not dominated by waves, such as in bays and lagoons
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 61
B. Coastal Landforms
1. Erosional Landforms
a. Headland
- an extension of land seaward from the general trend of the coast; a promontory, cape, or
peninsula
b. Sea Cliff (Wave-Cut Cliff)
- a cliff produced by wave erosion
c. Wave Cut Terrace
- a terrace cut across bedrock by wave erosion
d. Sea Cave
- a cave formed by wave erosion
e. Sea arch
- an arch cut by wave erosion through a headland
f. Sea stack
- a small, pillar-shaped, rocky island formed by wave erosion through a headland near a sea cliff
g. Tidal Inlet
- a waterway from open water to a lagoon
2. Depositional Landforms
a. Berm
- a nearly horizontal portion of a beach or backshore formed by storm waves
b. Coastal dunes
- most coastal dunes consist of a veneer of wind-blown sand overlying water-built beach ridges
c. Wave built terrace
- a terrace built up from wave-washed sediments; wave-built terraces usually lie seaward of a
wave-cut terrace
d. Tombolo
- a beach or bar connecting an island to the mainland.
e. Features built by Longshore Currents
- near-shore wave refraction creates Longshore Currents (these flow parallel to shore); obliquelybreaking waves also move Beach Drift (transported sand and pebbles) in a zig-zag manner down
PHYSICAL GEOLOGY LECTURE NOTES, PAGE 62
the beach
Types of Features Created by Longshore Currents Include:
Offshore Bar - an offshore, submerged, elongate ridge of sand or gravel built on the sea floor by
waves and currents
Spit - a sandy bar projecting from the mainland into open water; formed by deposition of
sediment moved by longshore drift
Barrier island - an elongate island of sand or gravel formed parallel to a coast
Beach - a deposit of wave-washed sediment along a coast between the landward limit of wave
action and the outermost breakers
3. Controlling Beach Erosion
- the major reason that beach erosion occurs is due to the alteration of the natural system by
people
Attempts at Beach Erosion Control have been through:
a. Hard Stabilization
- build Jetties (structures built at the entrances to rivers and harbors to "dam" beach drift and
prevent sedimentation within ship channels, etc.)
- build Groins (barriers built at right angles to the beach to trap sand moving parallel to the shore)
- build Breakwaters (barrier built parallel to the shore, which creates a quiet water zone near the
shoreline) and Seawalls (a barrier built along the shore to protect the shoreline from waves;
unfortunately, it also tends to increase coastal erosion seaward from the wall)
b. Beach Nourishment
- replenish the beach by adding large quantitites of sand
- beach nourishment is only viable in areas where there is dense development, with relatively low
wave energy, large supplies of sand, and where it will not greatly harm important ecosystems
c. Relocation
- relocate buildings in high hazard areas, and let nature reclaim the beach
4. Lagoon
- a shallow body of seawater separated from the open ocean by a barrier island or reef
5. Estuary
- a funnel-shaped inlet of the sea that is formed when a rise in sea level or subsidence of land
causes the mouth of a river to be flooded
- lagoons and estuaries are very important marine ecosystems, as they are rich in nutrients and
marine life