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 the characteristics of the original piece. Four important processes: Frost wedging, Unloading, Thermal expansion, and Organic activity.

Increasing Surface Area Increased surface area More surfaces available for weathering

Frost Wedging

Talus Slope Water expands 9% when frozen

Rock Slide Pic I-40 North Carolina

Sheeting Unloading Sheeting or exfoliation Reduction of overlying pressure causes fractures to develop parallel to surface topography

Half Dome Half Dome, Yosemite “Exfoliation Dome”

Table Rock 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/CO 2 to form carbonic acid: H 2 CO 3 H 2 O+CO 2 =H 2 CO 3 Acid Rain >CO 2 = >Acidity

Chemical Weathered Rock

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 Ganges River

Smog over China Beijing

Arctic warming 11 o F warming in winter months during 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 since 1978 Ice cap will be gone in 15 yrs.

Thinning Greenland ice cap Thinning up to 3 feet (!) per year

Silicate Mineral Susceptibility Rocks rich in quartz are very resistant Silica-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 Bora, Tahiti Knife-edged ridge Basalt; silica-poor

Monument Valley, Utah Quartz-rich, highly-resistant sandstone/quartzite layers

Spheroidal Weathering

Soil Composition

Types of Soils

Soil Profile

Soil Pic

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 in the 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 in Brazil

Bolivia

South Africa

Mexico

Unprecedented fires

Global fires

African Dust Exposed soil is prone to wind erosion

African Dust II

Urban Growth

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 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

Urban Flooding

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.