External Forces That Shape Our Planet

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External Forces That ShapeOur Planet
Presentation created by Robert L.
Martinez Primary Content Source World Geography
by McDougal Littell Images as cited.
http//www.uvm.edu/inquiryb/webquest/fa08/jlfishe
r/worksheets.html
http//www.ers.usda.gov/Briefing/AgAndEnvironment/
background.htm
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Weathering refers to physical and chemical
processes that change the characteristics of rock
on or near the earths surface.
www.csulb.edu
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Weathering occurs slowly over many years and even
centuries.
http//www.ask.com/wiki/Wind_erosion
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Weathering processes create smaller and smaller
pieces of rock called sediment. Sediment is
mostly identifiable as either mud, sand, or silt,
which is very fine particles of rock.
http//www.pubinfo.vcu.edu/masc/photos-2003-04/pho
tos-2003.htm
kohalacenter.org
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Processes that break rock into smaller pieces are
referred to as mechanical weathering.
skywalker.cochise.edu/wellerr/students/green-sand/
project.htm
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Mechanical weathering does not change the
composition of the rock, only its size and shape.
For example, when ice crystals build up in the
crack of a rock, they can actually create enough
pressure to fracture the rock into smaller
pieces.
http//kayty.glogster.com/glog-8007/
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All sorts of agents can break apart rocks. Frost
and even plant roots dig into crevices in the
rock, splitting it.
http//www.flickr.com/photos/42386373_at_N05/41733745
26/
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Human activities like road construction or
drilling and blasting in mining, are also
mechanical weathering forces.
http//gpssystems.net/tag/chilean-mine-disaster/
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Eventually, the smaller broken material will be
combined with organic material to become soil.
http//greenspade.com/how-to-collect-a-soil-sample

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Chemical weathering occurs when rock is changed
into a new substance as a result of interaction
between elements in the air or water and the
minerals in the rock.
http//www.shendapack.com/2011/04/27/chemical-weat
hering/
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Decomposition, or breakup, can happen in several
ways. Some minerals react to oxygen in the air
and begin to crumble. That is when iron rusts,
for example.
http//www.qub.ac.uk/geomaterials/weathering/cause
way/geologicalsuccessiol
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When sulfur and nitrogen oxides mix with water,
acid rain is formed. The increase of acid rain in
the 20th century is believed to be speeding up
some decomposition.
http//www.cvgs.k12.va.us/research/final/sresch02/
eevans/lit reviw.htm
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The location and the climate in which the rocks
are located have a great deal to do with how
rocks decompose.
http//www.aralam.com/html/geology.htm
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Climates that are warm and moist will produce
more chemical weathering than do cool dry areas.
http//www.qwickstep.com/search/chemical-weatherin
g-examples.html
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Rocks in cold dry and hot dry areas generally
experience more mechanical weathering than
chemical weathering.
http//geoimages.berkeley.edu/GeoImages/Johnson/La
ndforms/RocksWxing/ChemicalWxingGranitel
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Erosion occurs when weathered material is moved
by the action of wind, water, ice, or gravity.
http//www.grundfos.com/service-support/encycloped
ia-search/erosion-corrosion
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For erosion to occur, a transporting agent, such
as water, must be present. Glaciers, waves,
stream flow, or blowing winds cause erosion by
grinding rock into smaller pieces.
http//www.flickr.com/photos/40079018_at_N08/38104387
80/
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Material moved from one location to another
results in the lowering of some locations and
increased elevation in others.
http//www.uvm.edu/inquiryb/webquest/sp09/mbeatti
e/Erosion by wind.html
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For example, water might carry topsoil from a
hill into a river and gradually cause the river
to become more narrow.
http//savethesheyenne.org/erosion.htm
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Erosion in its many forms reshapes landforms and
coastal regions, as well as riverbeds and
riverbanks.
http//www.dinsdale.co.uk/regeneration_water_cours
es.cfm
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One form of water erosion occurs as water flows
in a stream or river.
http//www.sandhillstaskforce.org/Photo_Essay/Temp
_sandhills_photos
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The motion picks up loose material and moves it
downstream. The greater the force of water, the
greater the ability of the water to transport
tiny rock particles, or sediment.
http//www.thefrancisgallery.com/photosn2.php
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Another form of erosion is abrasion, the grinding
away of rock by transported particles. The
heavier the load of sentiment, the greater the
abrasion on the banks and riverbed.
//geology.about.com/od/geoprocesses/ig/mechweathe
ring/abrasion
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A third eroding action of water occurs when the
water dissolves chemical elements in the rock.
The composition of the rock changes as a result.
http//pulse.pharmacy.arizona.edu/9th_grade/cultur
e_cycles/earth_science/erosion.html
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Most streams erode both vertically and
horizontally, that is, the valley cut by a stream
gets deeper and wider, forming a V-shaped valley.
http//www.aegweb.org/i4a/pages/index.cfm?pageid4
083
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As the water slows, it drops the sediment it is
carrying. When a river enters the ocean, the
sediment is deposited in a fan-like landform
called a delta.
http//geographyfieldwork.com/CrowdedCoasts.htm
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Wave action along coastlines also changes the
land. Waves can reduce or increase beaches.
http//www4.ncsu.edu/eos/users/c/ceknowle/public/c
hapter12/part1.html
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Sediment deposited by wave action may build up
sandbars or islands. Wave action is so powerful
that in some locations, it erodes about three
feet of beach per year.
http//www.geograph.ie/photo/369272
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For some unfortunate people, a beach house with
an ocean view may end up in the ocean as a result
of wave action erosion.
http//www.learnnc.org/lp/editions/cede_sealevel/3
66
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In many ways, wind erosion is similar to water
erosion because the wind transports and deposits
sediment in other locations.
http//oceanworld.tamu.edu/resources/environment-b
ook/aeoliantransport
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Wind speeds much reach 11 miles per hour before
fine sediment can be moved. The greater the speed
of the wind, the larger the particles moved.
http//www.omafra.gov.on.ca/IPM/english/soil-diagn
ostics/erosion
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Dust storms are capable of carrying as much as
6,000 tons of sediment per cubic mile of air. As
the wind slows, the sediment is dropped.
http//www.pssac.org/SoilTeachingUnit/daytwo.htm
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Depending on the type of windborne sediment, new
landforms, such as sand dunes miles from
seashores and rocks sculpted into fantastic
forms, may be produced.
http//www.phototravels.net/egypt/egypt-v/egypt-v-
072.html
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Deposits of loess, windblown silt and clay
sediment that produce very fertile soil, are
found across the world. In northern China, for
example, the deposits are several hundred feet
deep.
http//www.pbase.com/dougsherman/image/93270863
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Extensive areas of loess are found in the
Mississippi Valley in the United States and in
the grasslands of Argentina.
http//www.igsb.uiowa.edu/browse/loeshill/loeshill
.htm
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A glacier is a large, long-lasting mass of ice
that moves because of gravity.
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Glaciers form in mountainous areas and in regions
that are routinely covered with heavy snowfall
and ice.
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In mountain regions, glaciers move downslope as a
result of gravity.
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Glaciers such as ice caps and ice sheets move
from the highest point on land toward the lowest
point.
http//newglobalwarmingeffects.com/2009/11/16/disa
ppearing-arctic-ice-caps/
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Glaciation is the changing of landforms by slowly
moving glaciers. As a glacier moves, several
types of erosion occur.
http//web.arc.losrios.edu/borougt/GlaciationDiag
rams.htm
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Rocks caught underneath the glacier are ground
into finer and finer particles. Some particles
are so small that they are called rock flour,
which is one component of soil.
http//ana20cristina.blogspot.com/2009/03/gif-letr
as-numeros-y-simbolos-en-rombos_4508.html
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Massive glaciers also cut U-shaped valleys into
the land.
http//ed101.bu.edu/StudentDoc/current/ED101sp09/s
andra06/Valley.html
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On top of or within the ice are other rocks
carried by the glacier. When the glacier melts,
these rocks are left behind.
http//serc.carleton.edu/details/images/22149.html

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Rocks left behind by a glacier may form a ridge
or a hill called a moraine. Moraines can be found
on the sides, down the center, or at the leading
edge of a glacier.
http//oceanworld.tamu.edu/students/iceage/iceage1
.htm
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Inside or under the glacier may be tunnels formed
by running water. These tunnels fill up with
sediment dropped by the water.
http//www.ens-newswire.com/ens/jul2010/2010-07-08
-01.html
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When the ice melts, it leaves a long snakelike
ridge called an esker. Sometimes blocks of ice
are trapped in the sediment. They melt slowly and
leave behind a dent or a depression in the
ground.
http//robinsonroom.blogspot.com/2010/06/glacial-f
eatures-photos.html
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These depressions are called kettles. The kettles
may be filled with water forming a small lake.
http//geology.about.com/od/glaciers_ice/ig/glacie
r-pictures/kettles
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Weathering and erosion are a part of the process
of forming soil. Soil is the loose mixture of
weathered rock, organic matter, air, and water
that supports plant growth.
http//www.mysciencebox.org/soilanalysis
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Organic matter in the soil helps to support the
growth of plants by providing needed plant food.
http//www.gardeninginfozone.com/organic-matter-fo
r-the-garden
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Water and air share tiny pore-like spaces in the
soil. When it rains, the pores are filled with
water. As the water evaporates, drains away, or
is used by the plants, the pores are filled with
air.
http//www.flickr.com/photos/dirkvdw/3752985815/
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The texture of the soil, the amount of organic
material called humus, and the amount of air and
water in the soil all contribute to the soils
fertility, its ability to nurture plants.
http//www.earthfort.com/products/supplies/denali-
gold-humus