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7/29/2019 Shaping Earth
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Shaping Earths Surface
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Importance of Weathering
Participates in the rock cycle
Used in the formation of soils
Helps in the movement of rock material over the Earths
surface.
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ErosionWeathering breaks the rocks into fragments
Erosion then transports the material to new places of the
Earth
This is the physical process of removing the weathered
material.
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TransportationThe movement of eroded materials by rivers, glaciers,
wind, or waves.
As material is transported the weathering and erosionprocess continues
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This famous natural bridge is an example of a landformcreated by the sculpturing power of weathering and erosion.
It is Rainbow Bridge in the Rainbow Bridge NationalMonument Utah.
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The piles of rocks and
rock fragments arounda mass of solid rock is
evidence that the solid
rock is slowly
crumbling away. This
solid rock that is
crumbling to rock
fragments is in theGrand Canyon,
Arizona.
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Mechanical Weathering
The physical breaking of rock material without anychange to their chemical composition
Exfoliation
Spalling off layers of rock
Caused by reduced pressure on rocks as material isremoved from above.
Frost wedging
Caused as pores or cracks become filled with water
and then freeze and thaw. As the process repeats cracks and pores become larger
Eventually the rock will break off.
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(A)Frost wedging and (B) exfoliation are two examples of
mechanical weathering, or disintegration, of solid rock.
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Growing trees can break, separate, and move solid rock. (A)Note how this tree has raised the sidewalk. (B) This tree issurviving by growing roots into tiny joints and cracks,which become larger as the tree grows.
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Chemical Weathering
The alteration of materials by chemical reactions which
do change the chemical composition of the material.
Oxidation
When oxygen reacts with minerals in rocks
Carbonation A reaction between carbonic acid and minerals in
rocks
Hydration
A reaction between water and the minerals in rocks. Dissolves material
Water combines with the mineral to form a hydrate
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Limestone caves develop when slightly acidic groundwater
dissolves limestone along joints and bedding planes,carrying away rock components in solution. (A) Joints and
bedding planes in a limestone bluff. (B) This stream hascarried away less-resistant rock components, forming a cave
under the ledge.
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Soils
Soil is a mixture of unconsolidated weathered Earthmaterials and humus
Humus
Decayed organic matter
Bedrock
Solid rock below the soil
LoamA soil that is a mixture of sand, silt, and clay
Also referred to as topsoil
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Mass Movement
Criteria
Materialbedrock that has been weathered and eroded
debris that is carried away during the massmovement.
RateThe speed at which the movement occurs
Type
FallSlip
Slump
Slide
Flow
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Creep
The slow downhill movement of soil down a steep
slope
Fall
material moves in free fall down a cliff
Slip - materials moving together along a surface
Slump - Movement along a curved surface
Slide - Movement along a plane parallel to the surface.
FlowMass movement of a liquid
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The slow creep of soil is evidenced by the strange
growth pattern of these trees.
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Running Water
Stream Channels
Move materials in 3 ways.
As dissolved material in a solution
As materials carried in suspension
As sand and larger materials rolled, bounced, and
slid along with a stream
Most of the erosion that a stream does is done by the
larger material that moves along with it on the streambed.
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Moving streams of water
carry away dissolved
materials and sedimentsas they slowly erode the
land.
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Stream Erosion and Deposit Features
Floodplain
The wide, level floor of the valley adjacent to astream that has been built by the stream over time.
This is the area that the stream will begin to moveinto when moisture is high (flood).
A young stream usually has a v shaped flood plainwhereas a mature stream has a flattened floodplain.
Delta
Where the stream empties into an ocean or a lake itloses all of its sediment carrying ability
The sediments are deposited at the mouth of thestream and form a deposit
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A river usually stays in its channel, but during a flood itspills over and onto the adjacent flat land called the
floodplain.
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Three stages in the aging
and development of a
stream valley, (A) youth,(B) maturity, and (C) old
age.
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The waterfall and rapids
on the Yellowstone
River in Wyoming
indicate that the river is
actively down cutting.
Note the V-shapedcross-profile and lack of
floodplain,
characteristics of ayoung stream valley.
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(A)Delta of Nooksack River, Washington. Note thesediment-laden water, and how the land is being builtoutward by river sedimentation. (B) Cross section showinghow a small delta might form. Large deltas are more
complicated than this.
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GlaciersA mass of ice on land that moves under its ownweight.
Origin of Glaciers As snow melts and refreezes it is turned into ice.
After years of repeated thawing of snow andrefreezing into ice, the weight above begins to pack
down the ice below. The increased pressure drives out air and reforms the
ice into a crystalline structure of interlocking icecrystals with a very high mass
Alpine glaciers form in high elevations Valley glaciers form and flow downhill through a
valley
Continental glaciers cover large areas of a continent.
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Valley glacier on Mount Logan, Yukon Territory.
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Glacial Erosion and Deposition
A glacier erodes material by:
Bulldozing
Abrasion
Plucking
Material; that is deposited by a glacier forms a
moraine
Plucking material produces a depression called a
cirque As abrasion continues material becomes ground into
fine sediment called rock flour.
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(A)A stream-carved mountainside before glaciation.
(B) The same area after glaciation, with some of the
main features of mountain glaciation labeled.
Wind
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Wind
Wind Erosion and Transportation
Wind abrasion is the sandblasting process that occurs asmaterial is carried along with wind.
Deflation is the picking up of loose materials from theEarths surface.
Wind Deposits
DunesA low mound or ridge of material sediments
Form where the wind that is carrying the sedimentencounters some obstruction
LoessVery fine dust or silt that is deposited over large areas.
The source of the material is thought to be rock flourfrom glacier action
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Ventifact
formation
by
abrasion
from one
or severaldirections
.