Weathering and Erosion

Weathering and Erosion

Weathering: The disintegration or decomposition of rocks on the Earth's surface.

Two types: Mechanical and Chemical

Mechanical Weathering

Mechanical Weathering: Breaks rocks by physical forces into smaller and smaller pieces, each retaining thecharacteristics of the original piece.

Four important processes: Frost wedging, Unloading, Thermal expansion, and Organic activity.

Increased surface areaMore surfaces available for weathering

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Frost Wedging

Water expands 9% when frozen

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I-40NorthCarolina

Unloading Sheeting or exfoliation

Reduction of overlying pressure causes fractures todevelop parallel to surface topography

Half Dome,Yosemite

“Exfoliation Dome”

Table Rock, South Carolina

Thermal Expansion

Heating and cooling of rocks in very hot desert regions cause stress on the outer surface of the rock. Mineral boundaries and stressed due to heating and cooling. Eventually, the outer shell will crack and fall off.

Death Valley, California

Organic Activity- Plant roots grow into rock fractures in search of water and mineral nutrients. As roots grow, fractures widen. - Burrowing animals move fresh material to the surface, allowing it to weather quicker than it would undergound. - Decaying organisms produce acids, which contribute to chemical weathering.

Chemical Weathering

- alters internal structure of minerals by removing/adding elements. - original material changes into something stable in the surface environment. - Water is the most important agent in chemical weathering. - can oxidize (like rust on a fender) and make a material weak & friable. - feldspar weathers into clay.

- combines w/CO2 to form carbonic acid: H2CO3

H2O+CO2=H2CO3

Acid Rain >CO2= >Acidity

Acid Rain Forest Damage

Coal mines in Germany

Haze over northeastern US

Power plants &automobiles

Phytoplankton bloom;probably pollution

Smog layer over New York State

India

Haze over India

GangesRiver

Smog over China

Beijing

Arctic warming

11oF warming inwinter monthsduring last 30 years

Retreating Iceland Glaciers

Iceland

2km retreat since 1973

All 40 of Iceland’s glaciers are retreating

Mt. Kilimanjaro, Africa

Mt. Kilimanjaro

82% decrease since1978

Ice cap will begone in 15 yrs.

Thinning Greenland ice cap

Thinning up to3 feet (!) per year

Rocks rich in quartz are very resistantSilica-poor rocks weather easily & quickly

quartz --> quartz feldspars --> soft clay minerals amphibole --> clay, hematite olivine --> hematite

Green Sand Beach, Hawaii

Weathered olivine minerals,not quartz sand

Bora Bora, Tahiti

Knife-edged ridge

Basalt; silica-poor

Monument Valley, Utah

Quartz-rich, highly-resistantsandstone/quartzite layers

Soil Composition

Types of Soils

Soil Profile

Controls on soil formation:

1) Parent material

-source of the weathered material - quartz-rich rocks will weather slower than an olivine-rich rock.

2) Time

- soils need time to evolve. The longer a soil has had time to form, the thicker it'll be. Soils need time to evolve before they are washed away.

3) Climate

- most important control on the formation of soils. - variations in temp and precip determine which process will dominate: mechanical or chemical weathering. And the rate of weathering. - Hot & Wet = thick layer of chemically weathered soil in same time as: Cold & Dry = thin mantle of mechanically weathered debris.

4) Plants and Animals

- supply organic matter to soils - bog soil is almost entirely organic, while desert soil lacks organics. - plants supply acids which increase the weathering/soil forming process. - microorganisms like fungi, bacteria also help - end product of organic decay is called humus.

5) Slope

- steep slopes encourage washing away of soil, so they tend to be very thin. - flats produce thick, dark, humus-rich soils due to the retaining of water and organic debris.

Humus

Decaying organic matter

In tropical regions, bacteria consume humus inthe soil, so the soil itself is nutrient poor.

Soil is slow to regenerate.

Central South America

9/19/2001

Fires

Smoke

Tan = deforestation

Deforestation

Deforestation

Deforestation in Brazil

Bolivia

Bolivia

Bolivia1986 2002

South Africa

Mexico

Unprecedented fires

Global fires

African DustExposed soil is prone to wind erosion

African Dust II

Urban Growth

1991 1995

Cairo

The population of the Cairo metropolitan area has increased from less than 6 million in 1965 when the first picture was taken, to more than 10 million in 1998 (United Nations Population Division, World Urbanization Prospects, the 1999 revision). Population densities within the city are some of the highest in the world and the urban area has doubled to more than 400 square km during that period. Extraordinary rates of population growth are expected to continue, with a predicted population of around 14 million by 2015.

Iraq

Today, river flow into the Mesopotamian marshlands has been cut by 20-50 percent, and the spring floods that sustained the marshlands have been eliminated. The end result is what was once a lush wetland environment roughly the size of the state of New Jersey has been reduced by about 85 percent in area to roughly the size of the small island nation of the Bahamas. What was once a vast, interconnected mosaic of densely-vegetated marshlands and lakes, teeming with life, is now mostly lifeless desert and salt-encrusted lakebeds and riverbeds.

US-Mexico

US

Mexico

San Jose, CA

This pair of images illustrates the rapid growth that occurred between 1973 and 1999 in San Jose, CA. From 1970 to 1996, the population of the city of San Jose increased from 459,000 to 839,000. This is reflected by an increase in urban areas in the above Landsat images, which show up as light blue.

Yellowstone

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The Paving Over of America

Water isn’t allowed to soak into the ground

Runoff

Winston-Salem, NC

Soil Erosion

Urban Flooding

More water, and more soil,than the river can handle.