Download Unit Two Part Two Notes

The Solid Earth
Unit Two
Part Two
We will cover
• - Soils
• - Plate Tectonics Theory
• - Earthquakes and Volcanoes
Stepping into the Soil
What is soil?
• Soil is an important product of
weathering.
• It covers most of land surfaces
• Very important resource
Characteristics of Soil
• Weathering produces a layer of
rock and mineral fragments called
regolith
• Soil is the part of the regolith that
supports plant growth.
Regolith - all material between
fresh bedrock and the ground
surface, including weathered
bedrock, deposits and soil.
Soil
• Soil has four major components:
•
•
•
•
Mineral matter (Broken-down rock)
Organic matter (humus)
Water
Air
Soil Texture
• Soils contain
particles of all
sizes.
• The texture of
a soil refers to
the particle
sizes in that
soil
How its formed
• How a soil is formed is dependent on:
•
•
•
•
•
Parent material
Time
Climate
Organisms
Slope
Parent Material
• Source of mineral matter in soil
• Can be either bedrock or
unconsolidated deposits
• Soil formed from bedrock is known as
residual soil.
• Soil formed from unconsolidated deposits
is called transported soil.
Time
• Time is important because the longer a
soil has been forming, the thicker it
becomes.
Climate
• Climate has the greatest effect on soil
formation.
• Climate also determines what can live on
and/or in the soil.
• The influence of climate is so great that soil
scientist have found that similar soils can be
produced from different parent materials in
the same climate.
Organisms
• Depending on what is in the soil, will
tell us how rich the nutrients of the soil
are.
• Plants are the main source of organic
matter in soil
Slope
• The amount of slope and direction of
slope influence the soil formation
greatly.
Soil Profile
• Soil varies in composition, texture,
structure, and color at different depths.
• These variations are divided into
zones known as soil horizons.
• A vertical section through all the soil
horizons is known as the
Types of Soil
•
Three common types
1. Pedalfer
2. Pedocal
3. Laterite
1. Pedalfer
• Forms in temperate areas
• B horizon in this form of soil is rich with
iron oxide and aluminum-rich clays.
2. Pedocal
• Drier conditioned soil that contains
less clay.
• Found in Western United State regions
3. Laterite
• Form in hot, wet tropical areas.
• Deeper soil due to rapid chemical
weathering.
What Is an Earthquake?
◆ An earthquake is the vibration of Earth
produced by the rapid release of energy
◆ Focus and Epicenter
• Focus is the point within Earth where the earthquake starts.
• Epicenter is the location on the surface directly above the
focus.
◆ Faults
• Faults are fractures in Earth where movement has occurred.
Focus, Epicenter, and Fault
Slippage Along a Fault
What Is an Earthquake?
◆ Elastic Rebound Hypothesis
• Most earthquakes are produced by the rapid release of elastic
energy stored in rock that has been subjected to great forces.
• When the strength of the rock is exceeded, it suddenly breaks,
causing the vibrations of an earthquake.
Elastic Rebound Hypothesis
What Is an Earthquake?
◆ Aftershocks and Foreshocks
• An aftershock is a small earthquake that follows the main
earthquake.
• A foreshock is a small earthquake that often precedes a major
earthquake.
Measuring Earthquakes
◆ Seismographs are instruments that
record earthquake waves.
◆ Seismograms are traces of amplified,
electronically recorded ground motion
made by seismographs.
◆ Surface waves are seismic waves that
travel along Earth’s outer layer.
Seismograph
Seismogram
Measuring Earthquakes
◆ Body Waves
• Identified as P waves or S waves
• P waves
- Are push-pull waves that push (compress) and pull (expand) in
the direction that the waves travel
- Travel through solids, liquids, and gases
- Have the greatest velocity of all earthquake waves
Measuring Earthquakes
◆ Body Waves
• S waves
• Seismic waves that travel along Earth’s outer
layer
- Shake particles at right angles to the direction
that they travel
- Travel only through solids
- Slower velocity than P waves
◆ A seismogram shows all three types of
seismic waves—surface waves, P
waves, and S waves.
Seismic Waves
Measuring Earthquakes
◆ Earthquake Distance
• The epicenter is located using the difference
in the arrival times between P and S wave
recordings, which are related to distance.
◆ Earthquake Direction
• Travel-time graphs from three or more
seismographs can be used to find the exact
location of an earthquake epicenter.
◆ Earthquake Zones
• About 95 percent of the major earthquakes occur in a few
narrow zones.
Locating an Earthquake
Measuring Earthquakes
◆ Historically, scientists have used two
different types of measurements to
describe the size of an earthquake
—intensity and magnitude.
◆ Richter Scale
• Based on the amplitude of the largest seismic
wave
• Each unit of Richter magnitude equates to
roughly a 32-fold energy increase
• Does not estimate adequately the size of very large
earthquakes
Measuring Earthquakes
◆ Momentum Magnitude
• Derived from the amount of displacement that occurs along
the fault zone
• Moment magnitude is the most widely used measurement for
earthquakes because it is the only magnitude scale that
estimates the energy released by earthquakes.
• Measures very large earthquakes
Earthquake Magnitudes
Destruction from Earthquakes
◆ The damage to buildings and other
structures from earthquake waves depends
on several factors. These factors include
the intensity and duration of the vibrations,
the nature of the material on which the
structure is built, and the design of the
structure.
Earthquake Damage
Destruction from Earthquakes
◆ Building Design
• Factors that determine structural damage
- Intensity of the earthquake
- Unreinforced stone or brick buildings are the most serious
safety threats
- Nature of the material upon which the structure rests
- The design of the structure
◆ Liquefaction
• Saturated material turns fluid
• Underground objects may float to surface
Destruction from Earthquakes
◆ Landslides
• With many earthquakes, the greatest damage to structures is from
landslides and ground subsidence, or the sinking of the ground
triggered by vibrations.
◆ Fire
• In the San Francisco earthquake of 1906, most of the destruction was
caused by fires that started when gas and electrical lines were cut.
Destruction from Earthquakes
◆ Short-Range Predictions
• So far, methods for short-range predictions of earthquakes have
not been successful.
◆ Long-Range Forecasts
• Scientists don’t yet understand enough about how and where
earthquakes will occur to make accurate long-term predictions.
• A seismic gap is an area along a fault where there has not been
any earthquake activity for a long period of time.
Earth’s Layered Structure
◆ Earth’s interior consists of three major
zones defined by their chemical
composition—the crust, mantle, and core.
◆ Crust
• Thin, rocky outer layer
• Varies in thickness
- Roughly 7 km in oceanic regions
- Continental crust averages 8–40 km
- Exceeds 70 km in mountainous regions
Earth’s Layered Structure
◆ Crust
• Continental crust
- Upper crust composed of granitic rocks
- Lower crust is more akin to basalt
- Average density is about 2.7 g/cm3
- Up to 4 billion years old
Earth’s Layered Structure
◆ Crust
• Oceanic crust
- Basaltic composition
- Density about 3.0 g/cm3
- Younger (180 million years or less) than the continental crust
Earth’s Layered Structure
◆ Mantle
• Below crust to a depth of 2900 kilometers
• Composition of the uppermost mantle is the igneous rock
peridotite (changes at greater depths).
Earth’s Layered Structure
◆ Core
• Below mantle
• Sphere with a radius of 3486 kilometers
• Composed of an iron-nickel alloy
• Average density of nearly 11 g/cm3
Earth’s Layered Structure
◆ Lithosphere
• Crust and uppermost mantle (about 100 km thick)
• Cool, rigid, solid
◆ Asthenosphere
• Beneath the lithosphere
• Upper mantle
• To a depth of about 660 kilometers
• Soft, weak layer that is easily deformed
Earth’s Layered Structure
◆ Lower Mantle
• 660–2900 km
• More rigid layer
• Rocks are very hot and capable of gradual flow.
Earth’s Layered Structure
◆ Inner Core
• Sphere with a radius of 1216 km
• Behaves like a solid
◆ Outer Core
• Liquid layer
• 2270 km thick
• Convective flow of metallic iron within generates Earth’s
magnetic field
Earth’s Layered Structure
Earth’s Interior Showing
P and S Wave Paths
Earth’s Layered Structure
◆ Crust
• Early seismic data and drilling technology indicate that the
continental crust is mostly made of lighter, granitic rocks.
◆ Mantle
• Composition is more speculative.
• Some of the lava that reaches Earth’s surface comes from
asthenosphere within.
Earth’s Layered Structure
◆ Core
• Earth’s core is thought to be mainly dense iron and nickel, similar
to metallic meteorites. The surrounding mantle is believed to be
composed
of rocks similar to stony meteorites.
Plate Tectonics
Continental Drift
◆ Wegener’s continental drift hypothesis
stated that the continents had once been
joined to form a single supercontinent.
• Wegener proposed that the supercontinent, Pangaea, began to
break apart 200 million years ago and form the present
landmasses.
Breakup of Pangaea
Continental Drift
◆ Evidence
• The Continental Puzzle
• Matching Fossils
- Fossil evidence for continental drift includes several fossil
organisms found on different
landmasses.
• Rock Types and Structures
- Rock evidence for continental exists in the
form of several mountain belts that end at one coastline, only
to reappear on a landmass across the ocean.
• Ancient Climates
Matching Mountain Ranges
Glacier Evidence
Continental Drift
◆ A New Theory Emerges
• Wegener could not provide an explanation of exactly what made
the continents move. News technology lead to findings which then
lead to
a new theory called plate tectonics.
Plate Tectonics
◆ According to the plate tectonics theory,
the uppermost mantle, along with the
overlying crust, behaves as a strong, rigid
layer. This layer is known as the
lithosphere.
• A plate is one of numerous rigid sections of the lithosphere that
move as a unit over the material of the asthenosphere.
Plate Tectonics
◆ Divergent boundaries (also called
spreading centers) are the place where two
plates move apart.
◆ Convergent boundaries form where two
plates move together.
◆ Transform fault boundaries are margins
where two plates grind past each other
without the production or destruction of the
lithosphere.
Three Types of
Plate Boundaries
Actions at Plate Boundaries
◆ Oceanic Ridges and Seafloor Spreading
• Oceanic ridges are continuous elevated zones on the floor of all
major ocean basins. The rifts at the crest of ridges represent
divergent plate boundaries.
• Rift valleys are deep faulted structures found along the axes of
divergent plate boundaries. They can develop on the seafloor or
on land.
• Seafloor spreading produces new oceanic lithosphere.
Spreading Center
Actions at Plate Boundaries
◆ Continental Rifts
• When spreading centers develop within a continent, the landmass
may split into two
or more smaller segments, forming a rift.
East African Rift Valley
Actions at Plate Boundaries
◆ A subduction zone occurs when one
oceanic plate is forced down into the
mantle beneath a second plate.
◆ Oceanic-Continental
•
Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental volcanic arcs form in part by volcanic
activity caused by the subduction of oceanic
lithosphere beneath a continent.
•
Examples include the Andes, Cascades, and
the Sierra Nevadas.
Oceanic-Continental
Convergent Boundary
Actions at Plate Boundaries
◆ Oceanic-Oceanic
• Two oceanic slabs converge and one descends
beneath the other.
• This kind of boundary often forms volcanoes on the ocean floor.
• Volcanic island arcs form as volcanoes emerge
from the sea.
• Examples include the Aleutian, Mariana, and
Tonga islands.
Oceanic-Oceanic
Convergent Boundary
Actions at Plate Boundaries
◆ Continental-Continental
• When subducting plates contain continental
material, two continents collide.
• This kind of boundary can produce new
such as the Himalayas.
mountain ranges,
Continental-Continental
Convergent Boundary
Collision of India and Asia
Actions at Plate Boundaries
◆ At a transform fault boundary, plates grind
past each other without destroying the
lithosphere.
◆ Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they roughly parallel the direction of plate
movement.
• They aid the movement of oceanic crustal material.
Transform Fault Boundary
Testing Plate Tectonics
◆ Paleomagnetism is the natural remnant
magnetism in rock bodies; this permanent
magnetization acquired by rock can be
used to determine the location of the
magnetic poles at the time the rock became
magnetized.
• Normal polarity—when rocks show the same magnetism as the
present magnetism field
• Reverse polarity—when rocks show the opposite magnetism as
the present magnetism field
Paleomagnetism Preserved
in Lava Flows
Testing Plate Tectonics
◆ The discovery of strips of alternating
polarity, which lie as mirror images across
the ocean ridges, is among the strongest
evidence of seafloor spreading.
Polarity of the Ocean Crust
Testing Plate Tectonics
◆ Earthquake Patterns
• Scientists found a close link between deep-focus earthquakes
and ocean trenches.
• The absence of deep-focus earthquakes along the oceanic ridge
system was shown to be consistent with the new theory.
Testing Plate Tectonics
◆ Ocean Drilling
• The data on the ages of seafloor sediment confirmed what the
seafloor spreading hypothesis predicted.
• The youngest oceanic crust is at the ridge crest, and the oldest
oceanic crust is at the continental margins.
Testing Plate Tectonics
◆ Hot Spots
• A hot spot is a concentration of heat in the mantle capable of
producing magma, which rises to Earth’s surface; The Pacific
plate moves over a hot spot, producing the Hawaiian Islands.
• Hot spot evidence supports that the plates move over the Earth’s
surface.
Hot Spot
Mechanisms of Plate Motion
◆ Scientists generally agree that convection
occurring in the mantle is the basic driving
force for plate movement.
• Convective flow is the motion of matter resulting from changes
in temperature.
Mechanisms of Plate Motion
◆ Slab-Pull and Ridge-Push
• Slab-pull is a mechanism that contributes to plate motion in
which cool, dense oceanic crust sinks into the mantle and “pulls”
the trailing lithosphere along. It is thought to be the primary
downward arm of convective flow in the mantle.
• Ridge-push causes oceanic lithosphere to slide down the sides of
the oceanic ridge under the pull of gravity. It may contribute to
plate motion.
Mechanisms of Plate Motion
◆ Mantle Convection
• Mantle plumes are masses of hotter-than-normal mantle material
that ascend toward the surface, where they may lead to igneous
activity.
• The unequal distribution of heat within Earth causes the thermal
convection in the mantle that ultimately drives plate motion.
Mantle Convection Models
The Nature of Volcanic Eruptions
◆ Factors that determine the violence of an
eruption
• Composition of the magma
• Temperature of the magma
• Dissolved gases in the magma
◆ Viscosity
• Viscosity is the measure of a material's resistance to flow.
The Nature of Volcanic Eruptions
◆ Viscosity
• Factors affecting viscosity
- Temperature (hotter magmas are less viscous)
- Composition (silica content)
1.
High silica—high viscosity
(e.g., rhyolitic lava)
2. Low silica—more fluid (e.g., basaltic lava)
The Nature of Volcanic Eruptions
• Pyroclastic Materials
• Pyroclastic materials is the name given to particles produced in
volcanic eruptions.
• The fragments ejected during eruptions range in size from very
fine duct and volcanic ash (less than 2 millimeters) to pieces that
weigh several tons.
The Nature of Volcanic Eruptions
• Pyroclastic Materials
• Types of pyroclastic material
- Ash and dust—fine, glassy fragments
- Pumice—frothy, air-filled lava
- Lapilli—walnut-sized particles
- Cinders—pea-sized particles
• Particles larger than lapilli
- Blocks—hardened lava
- Bombs—ejected as hot lava
The Nature of Volcanic Eruptions
• The three main volcanic types are shield
volcanoes, cinder cones, and composite
cones.
• Anatomy of a Volcano
• A volcano is a mountain formed of lava and/or pyroclastic
material.
• A crater is the depression at the summit of a volcano or that
which is produced by a meteorite impact.
• A conduit, or pipe, carries gas-rich magma to the surface.
Anatomy of a “Typical” Volcano
The Nature of Volcanic Eruptions
• Shield Volcanoes
• Shield volcanoes are broad, gently sloping volcanoes built from
fluid basaltic lavas.
• Cinder Cones
• Cinder cones are small volcanoes built primarily of pyroclastic
material ejected from a single vent.
- Steep slope angle
- Rather small in size
- Frequently occur in groups
Shield Volcanoes
Cinder Cones
The Nature of Volcanic Eruptions
• Composite Cones
• Composite cones are volcanoes composed of both lava flows
and pyroclastic material.
- Most are adjacent to the Pacific Ocean
(e.g., Mt. Rainier).
- Large size
- Interbedded lavas and pyroclastics
- Most violent type of activity
Composite Cones
Mount St. Helens Before and
After the May 18, 1980, Eruption
Profiles of Volcanic Landforms
Intrusive Igneous Activity
• Geologists conclude that magma originates
when essentially solid rock, located in the
crust and upper mantle, partially melts.
• The most obvious way to generate magma
from solid rock is to raise the temperature
above the level at which the rock begins to
melt.
Plate Tectonics and Igneous Activity
• The basic connection between plate
tectonics and volcanism is that plate
motions provide the mechanisms by which
mantle rocks melt to generate magma.
• Ocean-Ocean
• Rising magma can form volcanic island arcs in an ocean
(Aleutian Islands).
• Ocean-Continent
• Rising magma can form continental volcanic arcs (Andes
Mountains).
Convergent Boundary Volcano
Plate Tectonics and Igneous Activity
• The greatest volume of volcanic rock is
produced along the oceanic ridge system.
• Lithosphere pulls apart.
• Less pressure on underlying rocks
• Partial melting occurs
• Large quantities of fluid basaltic magma are produced.
Plate Tectonics and Igneous Activity
• Intraplate volcanism is igneous activity
that occurs within a tectonic plate away
from plate boundaries.
• Most intraplate volcanism occurs where a mass of hotter than
normal mantle material called a mantle plume rises toward the
surface.
• The activity forms localized volcanic regions called hot spots.
• Examples include the Hawaiian Islands and the Columbia
Plateau.
Kilauea, an Intraplate Volcano
1. Describe how the direction and
rate of movement for the North
American plate has affected the
local climate over the last 600
million years
2. Describe the differences between
oceanic and continental crust.
3. Using your knowledge of plate
tectonics, tell how our
community would be different if
there were no moving of plates.
How would our world look?
What kind of affect would it have
on our economy?