External Forces That ShapeOur Planet

Presentation created by Robert L. MartinezPrimary Content Source: World Geography by McDougal Littell

Images as cited. http://www.ers.usda.gov/Briefing/AgAndEnvironment/background.htm

http://www.uvm.edu/~inquiryb/webquest/fa08/jlfisher/worksheets.html

Weathering refers to physical and chemical processes that change the

characteristics of rock on or near the earth’s surface.

www.csulb.edu

Weathering occurs slowly over many years and even centuries.

http://www.ask.com/wiki/Wind_erosion

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.

kohalacenter.org http://www.pubinfo.vcu.edu/masc/photos-2003-04/photos-2003.htm

Processes that break rock into smaller pieces are referred to as

mechanical weathering.

skywalker.cochise.edu/wellerr/students/green-sand/project.htm

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/

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@N05/4173374526/

Human activities like road construction or drilling and blasting in mining, are also

mechanical weathering forces.

http://gpssystems.net/tag/chilean-mine-disaster/

Eventually, the smaller broken material will be combined with

organic material to become soil.

http://greenspade.com/how-to-collect-a-soil-sample

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-weathering/

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/causeway/geologicalsuccessiol

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

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

Climates that are warm and moist will produce more chemical

weathering than do cool dry areas.

http://www.qwickstep.com/search/chemical-weathering-examples.html

Rocks in cold dry and hot dry areas generally experience more

mechanical weathering than chemical weathering.

http://geoimages.berkeley.edu/GeoImages/Johnson/Landforms/RocksWxing/ChemicalWxingGranitel

Erosion occurs when weathered material is moved by the action of wind, water, ice, or gravity.

http://www.grundfos.com/service-support/encyclopedia-search/erosion-corrosion

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@N08/3810438780/

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/mbeattie/Erosion by wind.html

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

Erosion in its many forms reshapes landforms and coastal regions, as well as riverbeds and

riverbanks.

http://www.dinsdale.co.uk/regeneration_water_courses.cfm

One form of water erosion occurs as water flows in a

stream or river.

http://www.sandhillstaskforce.org/Photo_Essay/Temp_sandhills_photos

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

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/mechweathering/abrasion

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/culture_cycles/earth_science/erosion.html

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?pageid=4083

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

Wave action along coastlines also changes the land. Waves

can reduce or increase beaches.

http://www4.ncsu.edu/eos/users/c/ceknowle/public/chapter12/part1.html

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

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/366

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-book/aeoliantransport

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-diagnostics/erosion

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

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

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

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

A glacier is a large, long-lasting mass of ice that moves because

of gravity.

Glaciers form in mountainous areas and in regions that are routinely

covered with heavy snowfall and ice.

In mountain regions, glaciers move downslope as a result of

gravity.

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/disappearing-arctic-ice-caps/

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/GlaciationDiagrams.htm

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-letras-numeros-y-simbolos-en-rombos_4508.html

Massive glaciers also cut U-shaped valleys into the land.

http://ed101.bu.edu/StudentDoc/current/ED101sp09/sandra06/Valley.html

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

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

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

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-features-photos.html

These depressions are called kettles. The kettles may be filled with water forming a small lake.

http://geology.about.com/od/glaciers_ice/ig/glacier-pictures/kettles

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

Organic matter in the soil helps to support the growth of plants

by providing needed plant food.

http://www.gardeninginfozone.com/organic-matter-for-the-garden

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/

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 soil’s fertility, its ability to nurture plants.

http://www.earthfort.com/products/supplies/denali-gold-humus