The Shape of the Earths Surface Weathering

SHAPING THE EARTH’S SURFACE The Earth’s surface continually undergoes change through processes driven by external energy - energy from the sun. WEATHERING: the breaking down of rock material by physical or chemical means. EROSION: the transport of weathered materials (sediment). DEPOSITION: the laying down or depositing of sediment.

Physical (mechanical) vs. Chemical PHYSICAL WEATHERING= the mechanical breakdown of material (smaller pieces, same composition) CHEMICAL WEATHERING= the breakdown of material resulting from a change in chemical composition. (new materials, “separated” from whole)

TYPES of PHYSICAL WEATHERING ABRASION FROST ACTION EXFOLIATION or JOINT SHEETING ORGANIC ACTIVITY (PLANTS/ANIMALS) WETTING AND DRYING GRAVITY: LANDSLIDES

Abrasion The breakdown of material due to friction contact with another substance. Example: wind blowing sand into rocks, or water hitting rocks over time.

Frost Action Water gets into the cracks in rocks, and freezes and expands widening the cracks or breaking off pieces.

Exfoliation The repeated heating and cooling of rock due to sun, creates cracks and weakens rock.

Organic Activity (Plants & Animals) Plants and roots grow in cracks of rocks. As these grow the pressure on rock creates breaks. Animals, like Prairie Dogs gnaw on rocks. Breaks down rocks.

Wetting and Drying Rocks that contain Clay swell and Shrink as they absorb water, and then dry out, thus cracking the rocks.

Chemical Weathering Chemical weathering produces rock particles that have a different mineral makeup from the rock they came from. Example: Chemical weathering of granite changes feldspar minerals to clay.

Chemical Weathering Agents of chemical weathering include: Water”Hydrolysis” Oxygen “Oxidation” Carbon dioxide “Carbonation” “Plant Acids” Acid Rain “Sulfuric Acid”

Water “Hydrolysis” Most important agent of chemical weathering. Dissolves rock and turns it into clay

Plant Acids Lichens that grow on rocks produce chemical conditions that breakdown rock material.

Carbon Dioxide “Carbonic Acid” A gas found in air, carbon dioxide dissolves in rainwater to become carbonic acid. Carbonic Acid easily weathers limestone and marble.

Oxidation Oxidation is the chemical reaction associated with the presence of water and oxygen. Oxidation results in a weaker material.

Acid Rain “Sulfuric Acid” Burning of fossil fuels like coal, oil and gas has polluted the air with sulfur, carbon and nitrogen compounds. These compounds mix with water vapor in clouds to form acid.

RATES OF WEATHERING…how fast rock weathers over time. Depend on Following Factors: 1. Climate Both Chemical and Mechanical Weathering happen faster in WET CLIMATES. Rainfall provides water for chemical changes, and freezing/thawing.. Chemical weathering happens faster where the climate is both hot and wet. Example: Granite, an intrusive igneous rock weathers so slowly in cool climates, that it’s used for building stone. But in hot and wet climates, granite weathers faster and eventually crumbles apart. 2. Type of Rock-Some types weather faster - Mineral composition of rock determine how fast rock weathers. - Rock with minerals that dissolve easy weather faster. Example: Chemical Limestone, and other rocks containing calcite weather faster. 3. Surface Area or Particle Size - as weathering breaks apart rock, more surface area is exposed to weathering. 4. Weathering Agent - ie: Carbonic Acid weathers faster than hydrolysis.