Weathering and Erosion

Weathering

• The breakdown of the materials of Earth’s crust into smaller pieces.

Mechanical Weathering

• Process by which rocks are broken down into smaller pieces by physical means.

• Types of Physical weathering– Ice wedging– Plant roots– Animal activity (burrowing, moving soil)– Abrasion– Exfoliation

Ice Wedging

Ice Wedging

Plant Roots

Animal Activity

AbrasionThe scraping of materials together

Exfoliation• As pressure reduces on exposed rock, the

granite expands, resulting in long curved cracks and layers that peel away from the rock

Chemical Weathering

• The process that breaks down rock through chemical changes.

• The types of chemical weathering– Carbonation– Hydrolysis– Oxidation

Hydrolysis

• The interaction of water with other substances to weather rock

Oxidation• Iron combines with

oxygen in the presence of water in a processes called oxidation

• The product of oxidation is rust

Carbonation

• CO2 dissolves in rain water and creates carbonic acid

• Carbonic acid easily weathers limestone and marble

Carbonation, Continued

• Chemical weathering of limestone, breakdown of calcite

• Results in Karst Topography - A type of landscape in rainy regions where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams.

Features of Karst: Sinkholes

Features of Karst: Caves

Features of Karst: Disappearing Streams

Living Organisms

• Compounds from burning coal, oil and gas react chemically with water forming acids.

• Acid rain causes very rapid chemical weathering

Acid Rain

Erosion

• The process by which water, ice, wind or gravity moves fragments of rock and soil.

Water Erosion

• Rivers, streams, and runoff

Ice Erosion

• Glaciers

Wind Erosion

Mass Movements (Gravity)

• Landslides, mudslides, slump and creep, talus

landslide clip.mpeg

Talus

• Rocks at the base of a slope deposited by gravity

Rates of Weathering

How quickly or slowly a rock weathers and erodes depends on several factors:•Rock Composition•Exposure•Climate•Topography•Human Activity

Rock Composition

Some rocks are more resistant to weathering. For example, rocks comprised of quartz are more resistant to weathering since quartz is so stable, having crystallized last from the magma chamber.

Climate

Human Activity

Mining, Construction, Transportation, Recreational activities all contribute to wearing away and eroding rocks

TopographyThe elevation and slope of the land surface affects

its rate of weathering, for example:• Colder temperatures at higher elevations, more

ice wedging• Low elevations – more erosion by wave action• Steep slopes more affected by gravity

Exposure

• The more rock exposed, the more weathering can occur, so the rate of weathering increases.