Download Chapter 13: Introduction to Landform Study

Chapter 13: Introduction to Landform Study
I.
II.
The Unknown Interior
A. vertical structure of the Earth
1. crust: outermost solid layer of the Earth
a. thicker below continents than oceans
1) oceanic crust ~5-6 miles thick
2) continental crust > 3 times thicker
b. Moho (Mohorovicic discontinuity): boundary between the crust and
mantle below
2. mantle: layer of the Earth’s interior between the crust and the core;
extends downward ~ 1,800 miles
a. lithosphere: rigid outer layer of Earth that consists of the crust and
upper mantle
b. asthenosphere: plastic layer of the mantle that underlies the
lithosphere
c. mesosphere: lower mantle where rocks are again rigid
3. outer core: molten shell that underlies the mantle
4. inner core: solid, very dense center of the Earth composed of
iron/nickel or iron/silicate
B. Geographers Focus on the Surface
1. geographers focus on the zone of human habitation
2. interest in how deeper portion influences topography and other surface
features
Composition of the Crust
A. intro
1. minerals: naturally formed inorganic compounds and elements that
have a specific chemical composition and characteristic crystal
structure
2. magma: molten material in Earth’s interior
3. rock: solid material formed of aggregated mineral particles
4. outcrop: surface exposure of bedrock
5. bedrock: residual rock that has not experienced erosion
B. Igneous Rocks
1. igneous rock: rock formed by solidification of molten magma
a. shared trait: all have crystalline structure
b. slow cooling  large crystals; very coarse-grained appearance
c. rapid cooling  small, even microscopic crystals
2. extrusive igneous rocks: molten rock ejected onto Earth’s surface,
solidifying quickly in the open air
a. ejection of lava from volcanoes
b. oozing of magma from fissures
c. basalt: dark, fine-grained; most common of extrusive igneous rocks
3. intrusive igneous rocks: rocks that cool and solidify beneath Earth’s
surface
a. also called plutonic rocks
Chapter 13: Introduction to Landform Study – p. 1 of 5
b. originally buried intrusive rocks may subsequently come to surface by
being pushed up or by being exposed by erosion
c. granite: light colored, coarse-grained; most common of intrusive
igneous rocks
C. Sedimentary Rocks
1. sedimentary rock: rock formed by sediment that is consolidated by
the combination of pressure and cementation
a. mechanical and chemical processes cause rocks to disintegrate
b. resulting sediment may be transported by water, wind, ice, and/or
gravity
c. sediments, often sorted by size, are deposited in quiet body of water,
especially ocean floor
d. weight of thick deposits causes pressure and results in compaction
and cementation of sediments into rock
2. strata: more or less distinct horizontal layers of sediment
a. strata are characteristic feature of sedimentary rocks
b. although originally deposited and formed horizontally, strata may
subsequently be uplifted, tilted and deformed
3. sedimentary rock is classified based on how it is formed:
a. mechanically: formed by the compaction of fragments of pre-existing
rocks
1) fragments may range in size from boulders to clay
2) most common types:
a) shale: composed of silt and clay particles
b) sandstone: composed of compacted sand grains
b. chemically: formed by precipitation of soluble materials
1) calcium carbonate: most common cementing substance
2) limestone: most widespread type
c. organically: formed from accumulated remains of dead plants and
animals
1) coal
2) limestone
D. Metamorphic Rocks
1. metamorphic rocks: rock that has been drastically changed by heat
and/or pressure
a. structure, texture, composition and appearance are altered
b. cooking process causes mineral components to be recrystallized and
rearranged
2. foliation: banding that gives metamorphic rocks a wavy-layered
appearance
3. metamorphic rocks:
a. marble (from limestone)
b. quartzite (from sandstone)
c. slate (from shale)
4. most common metamorphic rocks (high degree of metamorphism;
original rock unknown)
Chapter 13: Introduction to Landform Study – p. 2 of 5
a. schist – very narrow foliations
b. gneiss – broad foliations
E. Relative Frequency of Rock Classes
1. sedimentary
a. most common exposed bedrock
b. 75% of the continents
c. sediments cover nearly all the seafloor
d. thin layer: averages < 1.5 miles
e. 5% total volume of crust
2. igneous rock make up bulk of crust
3. enormous amount of metamorphic rock beneath the crustal surface
F. Focus: Common Rock-Forming Minerals
1. only a few dozen of the 3,500 recognized minerals are important
constituents of the Earth’s crust
2. 7 principal categories of rock-forming minerals:
a. silicates
1) compose bulk of rocks of crust
2) combine 2 most abundant elements of the lithosphere:
a) oxygen
b) silicon
3) hard and durable
4) most abundant:
a) feldspars
b) quartz
b. oxides
1) element combined with oxygen
2) most widespread are those that combine with iron, and are major
sources of iron ore
a) hematite
b) magnetite
c. sulfides
1) composed of sulfur in combination with 1 or more other elements
2) includes many of most important ore minerals
a) galena (lead)
b) sphalerite (zinc)
c) chalcopyrite (copper)
3) abundant in veins
d. sulfates
1) minerals that contain sulfur and oxygen in combination with some
other element, principally calcium
2) mostly found in sedimentary rocks
e. carbonates
1) composed of one or more elements in combination with carbon
and oxygen
2) common in sedimentary rocks
f. halides
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III.
IV.
1) salty minerals
2) least widespread
g. native elements
1) minerals that occur as discrete elements
2) precious metals: gold, silver
Some Critical Concepts
A. Basic Terms
1. topography: surface configuration of Earth
2. landform: individual topographic feature, of whatever size
3. geomorphology: study of the characteristics, origin, and development
of landforms
4. relief: difference in elevation between the highest and lowest points in
an area
a. maximum world relief:
1) 12-13 miles
2) between top of Mount Everest and bottom of Mariana Trench
B. Uniformitarianism
1. uniformitarianism: processes that formed the topography of the past
are the same ones that have shaped contemporary topography
2. most processes are permanent and slow acting
3. development of landforms is a virtually endless event
C. Geologic Time (Fig 13-18)
1. geologic history divided into 4 major eras:
a. Precambrian – 7 or 8 times longer than the 3 other eras combined
b. Paleozoic
c. Mesozoic
d. Cenozoic: 66 billion years ago to present
2. eras are divided into periods
3. more recent periods are divided into epochs
4. present: Cenozoic (era)  Quaternary (period)  Holocene (epoch)
D. People and the Environment: The Magnitude of Geologic Time
1. Earth is ~4.6 billion years old
2. geomorphic processes generally operate with excruciating slowness,
but the vastness of geologic history provides a suitable time frame for
their accomplishments
The Study of Landforms
A. basic elements of a study of landforms
1. structure
a. nature, arrangement, and orientation of the materials making up the
feature being studied
b. essentially the geologic underpinning of the landform
2. process
a. actions that have combined to produce the landform
b. geologic, hydrologic, atmospheric, and biotic
3. slope
a. fundamental aspect of shape for any landform
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b. reflection of the contemporary balance among the various
components of structure and process
4. drainage: movement of water either over Earth’s surface or down into
the soil and bedrock
V. Internal and External Geomorphic Processes
A. internal processes
1. fueled by internal heat
2. result in crustal movements of various kinds
3. constructive, uplifting, building forces that tend to increase the
relief of the land surface
4. internal processes:
a. plate tectonics
b. vulcanism
c. diastrophism (folding and faulting)
B. external processes
1. fueled by sources either in the atmosphere or in the oceans
2. their behavior may be significantly influenced by exiting topography
3. wearing down or destructive forces that tend to diminish
topographic irregularities and decrease the relief of Earth’s surface
4. external processes:
a. weathering
b. mass wasting
c. erosion/deposition
C. internal and external processes work more or less in opposition to one
another
VI. The Question of Scale
A. recognizable features and associations vary considerably depending on
the scale of the observation
B. Focus: An Example of Scale
1. large scale: smaller area, more detail
2. small scale: larger area, less detail
VII. The Pursuit of Pattern
A. a prime goal of geographic study: detect patterns in the areal distribution
of phenomena
1. Fig 13-23: major landforms assemblages of the world
B. overall, global distribution of topography is very disordered and
irregular
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