Weathering Erosionand Deposition

Weathering

• The breakdown of rock into smaller pieces (Sediment)

Mechanical Weathering

• Rocks broken into sediment by physical means

• Types – Frost heaving and Frost wedging– Plant roots– Friction and impact– Burrowing of animals– Temperature changes

Frost Wedging

Expansion of cracks in rock due to freezing ice

Frost Heaving

Wet soil freezes, pushing up the ground above

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• Oxygen makes iron

rust.• Rust is unstable

Carbon Dioxide

• CO2 in soil dissolves in rain water and creates carbonic acid

• Easily weathers limestone and marble

Living Organisms

• Lichens produce weak acids

Acid Rain• Compounds from burning fuels (NOx SO4)

form acids in rain.

• 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 over time to form different layers.

• OM broken down by FBI is called Humus

Soil Profile

• A cross section of soil that shows the different layers, called horizons.

• There are 4 different horizons

O horizon

• Top layer

• 100% organic matter (living or dead)

• No sediment, therefore not soil.

A Horizon

• The top layer of soil, often referred to as topsoil.

• Dark in color because it has lots of organic matter.

• Also contains roots and animals.

B Horizon

• Middle layer of soil

• Lighter because it has less organic matter

• Some plant roots

• Leeching – water bringing nutrients from one layer into the next

C Horizon

• Deepest layer of soil

• Contains no Organic matter, only weathered rock.

• Little to no nutrients.

Soil Profiles (cont)

• Soil profiles differ in different areas

• 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.

Erosion Factors

• Rate of Rain– More rain More Erosion

• Slope of land– Steeper land More Erosion

• Plants– Fewer Plants More Erosion

Humans

• Increase erosion– Plowing– Overgrazing animals– Clear cutting forests

• Decrease Erosion– No-Till farming– Contour Farming– Terracing– Selective cutting of forests

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.

• Water flows in wide sheets rather than streams

• Because the water has less energy, it deposits much of its sediment

Ice Erosion

• Glaciers

Glaciers

• Valley Glaciers - small glaciers between mountains

• Leave U-shaped valley.

• Continental Glaciers - large glaciers that cover vast areas.

• Currently cover 10% of earth

Glacial Erosion

• 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

Glacial Deposition

• Glaciers drop their sediment (till)as they melt.

• Moraines - pile of sediment perpendicular to movement

• Eskers – winding pile of sediment parallel to movement

• Drumlin – Streamlined piles of sediment parallel to movement

• Glacial Erratic - single large rock dropped by glacier

Wind Erosion

Wind Erosion

• Deflation – Wind picks up sediment• Abrasion – Wind carried sediment acts as

a sand blaster• Loess – fine sediment deposited by

slowing wind• Dunes – piles of sand constantly moved

by wind

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.

Landslides & Rockslides

• Large areas of rock/soil break loose from a steep slope and move quickly downhill.

• Occur often after earthquakes or heavy rains.

• Fan-shaped piles of sediment at the bottom of a slope is good evidence of slides

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