Weathering and Erosion

Weathering The breakdown do the materials of Earth’s crust into smaller pieces called Sediment.

Mechanical Weathering Process by which rocks are broken down into smaller pieces by external conditions. Types of Mechanical weathering Frost heaving and Frost wedging Plant roots Friction and impact Burrowing of animals Temperature changes

Frost Wedging

Frost Heaving

Plant Roots

Friction and Repeated Impact

Burrowing of Animals

Temperature Changes

Chemical Weathering The process that breaks down rock through chemical changes. The agents of chemical weathering Water Oxygen Carbon dioxide Living organisms Acid rain

Water Water weathers rock by dissolving it

Oxygen Iron combines with oxygen in the presence of water in a processes called oxidation The product of oxidation is rust

Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble

Living Organisms Lichens that grow on rocks produce weak acids that chemically weather rock

Acid Rain Compounds from burning coal, oil and gas react chemically with water forming acids. Acid rain causes very rapid chemical weathering

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

Features of Karst: Sinkholes

Features of Karst: Caves

Features of Karst: Disappearing Streams

Soil Soil is the product of weathering rocks and dying living things. Mixture of sediment and organic matter Plants, as well as Fungi, Bacteria, and Invertebrates mix soil to form different layers.

Soil Profile A cross section of soil that shows the different layers, called horizons. There are 3 different horizons characterized by how much organic matter is present.

A Horizon The top layer of soil, often referred to as topsoil. Dark in color because it has the most organic matter. Also contains roots and animals. The most evolved layer.

B Horizon Middle layer of soil. Much lighter because it has little to no organic matter. Some plant roots reach this layer. Minerals from topsoil’s organic matter is leeched into this layer.

C Horizon First layer of soil above the bed rock. Contains no Organic matter, only weathered rock. Also contains little to no nutrients.

Soil Profiles (cont) Soil profiles differ based on the climate in the area. Thickness of the various layers depends on the climate type as well as the plant/animal activity above.

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

Water Erosion Rivers, streams, and runoff

Rills and Gullies Rill and Gully Erosion occur when water moves over steep areas, carving out channels. Rills are formed by small streams. Gullies are formed as rills become broader and deeper due to more water. The fast moving water removes sediment.

Sheet Erosion Sheet erosion occurs in flat areas where the water slows down. Because the water has less energy, it drops much of its sediment, covering the area like a sheet.

Ice Erosion Glaciers

Glaciers Valley Glaciers - small glaciers that exist between mountains Leave a small U-shaped valley. Continental Glaciers - large glaciers that cover vast areas. Currently cover 10% of earth

Erosion and Deposition Glaciers erode as they move. They can pick up sediment and move it great distances - Plucking They can also scrape the surface rock resulting in striations Glaciers drop their sediment as they melt. Moraines - pile of sediment perpendicular to movement Eskers - pile of sediment parallel to movement Glacial Erratic - single large rock dropped by glacier

Wind Erosion

Wind Erosion Acts as a sand blaster. Wind carries small pieces of sediment and smashes them into rock or other hard surfaces - Abrasion When the wind slows it deposits this material in thick layers of fine sediment - Loess Deposition occurs on a small scale behind objects

Gravity Erosion (Mass Movements) Slumps, Creeps, Rockslides and Mudslides

Slumps Occurs on a steep slope when loose materials slide down the slope in one large mass. Layers under the soil are weakened due to erosion or earthquakes. Leaves curved scar in soil

Creep Slow mass movement down a less steep slope. Often caused by repeated thaw melt cycles. Causes tree and fence-posts to lean downhill.

Rockslides Rockslides occur when large piece of rock break loose from a steep slope and roll quickly downhill. Occur often after earthquakes or heavy rains. Piles of broken rocks at the bottom of a slope is good evidence of a rockslide.

Mudflow Occur as mixtures of water and sediment flow down a slope. Occur after heavy rains in areas of thick dry sediment. Water and sediment forms a thick paste that has lots of momentum, and causes lots of damage. http://www.youtube.com/watch?v=51C7vEAVbxk