Unit 4: Weathering, Erosion, Deposition (WED) Destructive Forces

DESTRUCTIVE FORCES! Plate tectonics builds the earth surface up But what goes up, must come down! Once exposed to the air, water or wind, rock will begin its destructive cycle It will weather down!

What is weathering? The breaking down of rock due to physical and/or chemical changes in the rock as it is exposed to the atmosphere Occurs at the interface between the atmosphere and the lithosphere Results in smaller pieces of rock called sediments

Physical weathering Results in a change in appearance of rock (size, shape, state) Types include: frost action, plant action, pressure unloading

Frost action Occurs in a cold and moist climate Alternating freezing and melting of water in the rock cracks the rock

Plant action Plant roots grow into small cracks in rock and widen them

Pressure unloading Rock cracks when pressure over the rock is removed

Chemical Weathering Results in a change in chemical composition of the rock Types include: oxidation, acid reactions, and hydrolysis

Oxidation Addition of oxygen to metal…results in rust (iron oxide)

Hydrolysis Chemical weathering by reaction of water with other substances When certain minerals are exposed to water they dissolve into ions…ex: feldspar Feldspar will chemically weather into clay (kaolinite) Water will help any chemical reaction

Acids Gases such as sulfur dioxide, nitrogen dioxide, carbon dioxide will dissolve in rainwater forming acid rain (sulfuric acid, nitric acid, and carbonic acid -a weak acid) Calcite will dissolve completely in carbonic acid-thus chemically weather any rock containing this mineral easily Acid rain which forms naturally, for example volcanic activity, or by pollutants, harms any exposed rock, buildings and monuments

Caves Form!

End RESULT of Weathering: SEDIMENTS! INCLUDES-CLAY, SILT, SAND, PEBBLES AND COBBLES SEE ESRT P6,7

What can affect the rate of weathering? Size of the sediment Type of mineral (hardness) Temperature Humidity (amount of moisture present)

How does weathering connect to the rock cycle?

Sediments form sedimentary rocks…

What is soil? A mixture of weathered rock and organic remains (humus) Forms at interface between the atmosphere and the lithosphere

How does soil form? 1st: rocks weathers 2nd: leaching of minerals adds nutrients to lower layers from top layer 3rd: biological activity such as decomposition add organic matter (humus) to soil, soil is mixed by earthworms Takes 500 to 1000 years to form

Soil Horizons A=topsoil (fertile layer) B=Subsoil C=Parent Rock Types: Residual or transported

What measure can be done to conserve Soil? Soil is a natural resource and must be protected! Several methods exist to protect soil such as contour farming, no-till farming, terracing, and crop rotation These all prevent erosion of the topsoil by wind or water

Why is it important to protect? We need it to sustain ecosystems Producers take nutrients from the soil and convert it to food with the help of sunlight Basis of the food chain