Transcript Chapter 13: Intro to Landforms

Chapter 13: Intro to Landforms
• Structure of the Earth
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Crust
Mantle
Outer Core
Inner Core
• Rock Classification
– Igneous
– Sedimentary
– Metamorphic
• Landform Study
– Geomorphology
– Internal vs External Processes
– Uniformitarianism
• Geologic Time
Temperature & pressure increase
inward.
Heat from energy released by
decaying radioactive elements.
Dense inner core, surrounded by three layers
of varying composition and density.
Structure of Earth
• Crust—1% of Earth’s mass
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Outermost shell of varying degree of thickness (4 – 40 miles)
Oceanic crust is thinner, but denser than continental crust
Mixture of rock types
Moho: Mohorovicic Discontinuity. At the base of the crust,
different mineral composition.
• Mantle
– 1800 miles deep
– Largest portion of the Earth by volume (84%)
– Three Layers: Lithosphere, Asthenosphere, Lower Mantle
• Inner & Outer Core
– Outer core is probably molten (liquid), 3100 miles
– Inner core is solid (pressure), 900 miles in radius, 4100 miles deep
Composition of Earth
• Minerals—form the basis of rocks; must be solid and naturally found
in nature, inorganic, specific chemical composition that doesn’t change
– Silicates
• Most important
• Most of the rocks in the crust are comprised of this type of material
• Combination of oxygen and silicon (light & dark)
– Oxides
• An element combined with oxygen
• Most common combine with iron (hematite, magnetite, limonite—iron ore)
– Sulfides
• Sulfur combined with some other element
• Lead, copper, zinc
– Sulfates
• Sulfur, oxygen and some other element, often calcium (light in color)
– Carbonates
• Also light in color , calcium and carbon, calcium carbonate--limestone
– Halides
• Least common; salts (including common table salt)
Quartz crystal.
A common
silicate.
Pyrite crystal (iron and sulfur).
A common sulfide
material.
Rocks
• Solid, combination of mineral materials
• Solid rock can be found at the surface, an
outcrop
• Solid rock can be buried as bedrock
covered by a layer of broken rock, regolith
• Soil is the upper portion of regolith
Rock Types:
Igneous, Sedimentary, Metamorphic
• Igneous
– Rock that cools and hardens from molten
material (magma or lava)
– Magma is molten rock below surface
– Lava is molten rock above surface
– Determined by mineral composition & texture
• Mineral—how much silica?
• Texture—where and how did it cool?
– Intrusive vs Extrusive (Plutonic vs Volcanic)
Granite—most common type of Plutonic Rock
Basalt—most common type
Of Volcanic Rock
Massive outcrops of granite, Sylvan Lake reservoir, Black Hills, SD
Granite-note the glassy quartz grains (intrusive or plutonic rock).
Snake River Canyon. Southern Idaho. Several layers of basalt are visible on the
exposed sides of the canyon.
Black basalt (extrusive or volcanic rock).
Very porous, black basalt
• Sedimentary
– External processes causing rocks to
disintegrate
– Weathering
– Produces fragments, or sediment which are
relocated (water, wind, ice, gravity)
– Build in thickness and coalesce through
compaction and chemical cementation
– Can include organic and inorganic materials
– Material builds into distinct layers, or strata;
creates distinctive stratification structure
Compaction (a)
Cementation (b)
• Detrital (clastic)
– From preexisting rocks
– Gravel, silt, sand, clay
– Shale—very fine silt and clay
– Sandstone—compacted sand-size grains
• Chemical
– From chemical reactions; could be precipitation
of solids from ions in solution or more
complicated chemical reactions
– Limestone
• Organic
– Compacted remains of dead plant material
– coal
(a)Sandstone cliffs in southeastern Utah.
(b)Typical, light colored sandstone.
Sedimentary strata (mostly limestone and shale) that have been folded and
tilted into an almost vertical orientation on Mt Angeles, Olympic Mtns of
Limestone and shale in a road cut, Lyons, CO.
Visible are the nearly horizontal strata of each material
Sample of limestone with an abundance of small fossil mollusks, such as
snails.
• Metamorphic Rock
– Change of igneous or sedimentary rock
– Physically or chemically changed (heat,
pressure, chemicals)
– Caused by
• Contact with magma (common to find metamorphic
rock near granite)
• Pressure (common along boundaries of crustal
plates)
• Hydrothermal (mineral rich fluids in rock cracks)
– Some change predictably:
• Limestone to Marble
• Sandstone to Quartzite
• Shale to Slate
Bedrock exposed, NE CA near Alturas, shows light brown basalt on top of colorful layer
of tuff (a volcanic rock, formed by volcanic ash). Basalt extruded onto the tuff in
molten form and ‘cooked’ the upper layer of tuff. Color shows the difference
between the metamorphosed rock and that that remained unchanged.
10,000 feet below sea level, along the Mid-Atlantic Ridge. This is a ‘black smoker’
or vent releasing hot volcanic fluids, leading to hydrothermal metamorphism.
The president’s heads at Mt. Rushmore are carved out of granite. Right
below is a much older metamorphic rock, a mica schist, into which the
granite forming material intruded.
Mica schist.
• Foliated Metamorphic Rock
– When the minerals show a clear alignment or
orientation
– Banded, wavy
– Slate, schist, gneiss
• Nonfoliated Metamorphic Rock
– Usually a single mineral in its original form
– Sandstone, limestone
Large outcropping of phyllite, Merced River Canyon. Phyllite is a foliated
metamorphic rock. Thin parallel layers of minerals can be seen.
Close up view of phyllite.
Typical gneiss.
Outcrop of banded gneiss, Greenland. One of the oldest areas of rock on
Earth, about 3.8 billion years old.
The Rock Cycle:
On-going
recycling of the
Earth’s
lithosphere.
• Patterns to the distribution of rock type
– Most of the exposed rock on continents is
sedimentary
– However, most of the continents are
comprised of granite (intrusive igneous).
– Ocean floors are mostly comprised of basalt
(extrusive igneous).
– Means that ocean plates are denser, heavier,
so it will be subducted into asthenosphere.
• Isostasy
– Lithosphere is ‘floating’ on the denser, pliable
asthenosphere
– If mass is added to the lithosphere, it will sink
– If mass is removed, lithosphere will rise
– Called isostatic adjustment
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Deposition of sediment
Accumulation of ice in a glacial ice sheet
Weight of water trapped behind dam
Ice sheet melts, material erodes away, water drains
Florida: water is dissolving limestone underneath
the surface, so isostatic uplift has resulted.
• Alaska: melting of glaciers
Landform Study
• Landforms comprise the topography of an area
• Geomorphology-study of characteristics and development
of landforms
• Terminology:
– Structure: materials making up the landform
– Process: actions that have formed the landform
– Slope: relationship between a surface and the surrounding
landscape
– Drainage: movement of water
Montana’s Glacier National Park.
Produced by a variety of interacting processes, including glaciation.
St. Mary Lake, with Citadel Mountain on the left and Fusillade Mountain in the
distance
Slope—abrupt cliffs of the volcanic backbone of the island of Bora-Bora.
• Processes at work are divided into two
categories:
– External—originate above surface of Earth:
weathering, mass wasting, erosion;
constructive, adding material to earth
– Internal—originate within the Earth:
volcanism, folding, faulting; destructive,
removing material from earth
• Uniformitarianism
– Present is key to the past
– Same processes at work today shaped the
earth in the past and will shape it in the future
– James Hutton, 1795
– Contrast to catastrophism—sudden upheavals
or change
– Uniformitarianism acknowledges different rates
of change
• Geologic Time
The importance of
scale in all geographic
inquiry.
1) Horseshoe Park, CO
2) Looking down on Horseshoe Park from
Trail Ridge Road
3) Aerial view of Mummy Range and part
of the Front Range
4) High-altitude view of CO
5) North America from satellite
Patterns in geomorphology