Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Erosion is the wearing away and removal of rock or sediment.

• Erosion occurs because gravity, ice, wind, and water sculpt Earth's surface. These are known as agents of erosion

• Of these four, water is the most important agent of erosion

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Gravity– Gravity causes water to flow downhill and rocks to

tumble down slopes.

– When gravity alone causes rock or sediment to move down a slope, the erosion is called mass movement

Erosion• Erosion of Earth’s Surface

– Agents of Erosion - Gravity• Types of Mass Movement

– Creep

» Occurs when sediments move slowly downhill

– Slump

» Mass of rock or sediment moves downhill, leaving a curved scar

» Slumps frequently occur on slopes that have been undercut by erosion, such as those above the bases of cliffs that have been eroded by waves.

Erosion

• Erosion of Earth’s Surface– Agents of Erosion- Gravity

• Types of mass movement– Mudslides

» A mass of wet sediment that flows downhill over the ground surface.

» Some mudflows can be thick and flow slowly downhill at rates of a few meters per day.

» Other mudflows can be much more fluid and move downslope at speeds approaching 160 km/h (common on slopes of volcanoes)

Erosion

• Erosion of Earth’s Surface– Agents of Erosion - Gravity

• Types of mass movement– Rock flows, rockslides, landslides

» Layers of rock break loose from slopes and slide to the bottom.

» The rock layers often bounce and break apart during movement.

» This produces a huge, jumbled pile of rocks at the bottom of the slope

Erosion

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Ice– In cold regions, if more snow falls than melts, it can form

large, deep masses of ice called glaciers.

– When a glacier becomes thick enough, its own weight causes it to flow downhill under the influence of gravity.

– As glaciers move over Earth's surface, they erode materials from some areas and deposit sediment in other areas

Erosion

• Erosion of Earth’s Surface– Agents of Erosion - Ice

• Glacial Erosion1. If underlying rock has cracks in it, the ice can pull out

pieces of rock. This is called plucking

2. These rocks remain in the ice and act like sandpaper as they are dragged over Earth’s surface. This scratching is the second way that glaciers can erode rock, and leave large grooves or smaller striations in the rock underneath.

Erosion

• Erosion of Earth’s Surface– Agents of Erosion - Ice

• Effects of Glacial Erosion– In mountains, valley glaciers can remove rock from the

mountaintops to form large bowls, called cirques (pronounced SURKS), and steep peaks.

– When a glacier moves into a stream valley, it erodes rock along the valley sides, producing a wider, U-shaped valley.

– Continental glaciers can scour large lakes and completely remove rock layers from the land's surface.

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Ice– Effects of Glacial Erosion

Cirque U-shaped valley

Erosion• Erosion of Earth’s Surface

– Agents of Erosion - Ice

• Glacial Deposition– When stagnant glacier ice melts or when ice melts at the

bottom of a flowing glacier or along its edges, sediment called till the ice was carrying gets left behind on Earth's surface.

– It is a mixture of different-sized particles, ranging from clay to large boulders.

– Sand and gravel deposits laid down by streams flowing from melting glaciers are called outwash (particles are all about the same size)

– Moraines are glacially formed accumulations of soil and rock

Glacial till

Source: glacialtill.wordpress.com

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Wind Erosion– When wind blows across loose sediments like silt and

sand, it lifts and carries it.

– Wind often leaves behind particles too heavy to move.

– This erosion of the land by wind is called deflation. Deflation can lower the land's surface by several meters.

Deflation

Source: eoearth.org

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Wind Erosion– Wind that is carrying sediment can wear down, or

abrade, other rocks just as a sandblasting machine would do.

– Abrasion by wind erosion can make pits in rocks and produce smooth, polished surfaces.

Wind abrasion

Source: earthonlinemedia.com

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Wind Deposition– Sediment deposition forms sand dunes along seashores

and in deserts.

– Sometimes, wind carries only fine sediment called silt. When this sediment is deposited, an accumulation of silt called loess (LOOS) can blanket Earth's surface

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Water – Water is divided into surface water and groundwater

– Surface water is also called runoff

– Sheet Flow

» When water flows downhill as a thin sheet, it is called sheet flow.

» This thin sheet of water can carry loose sediment grains with it, causing erosion of the land.

» This erosion is called sheet erosion.

Sheet flow on impervious road

Source: lakesuperiorstreams.org

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Surface Water– Rills and Gullies

» Rills are small channels cut into the sediment at Earth's surface, and carry more sediment than sheet flow.

» Gullies are rills whose channels are about 0.5 m across.

Rills

Source: confessteelmagnolia.blogspot.com

Gullies

Source: geog.uu.nl

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Surface Water– Streams

» Gullies often connect to stream channels.

» Streams can be so small that you could jump to the other side or large enough for huge river barges to transport products along their course.

» Most streams have water flowing through them continually, but some have water only during part of the year.

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Surface Water– Streams

» In mountainous and hilly regions, streams flow down steep slopes, which give them a lot of energy

» They often cut into the rock beneath their valleys.

» This type of stream typically has white-water rapids and may have waterfalls.

» As streams move out of the mountains and onto flatter land, they begin to flow more smoothly.

Stream

Source: kidsgeo.com

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Surface Water– Rivers

» Larger streams are called rivers

– Tributaries

» Streams and rivers can merge to form larger bodies called tributaries

Erosion

• Erosion of Earth’s Surface– Shaping Earth’s Surface

• Effects of surface water erosion– Over long periods of time, water moving in a stream can

have enough power to cut large canyons into solid rock. (V-shaped valleys)

– Waterfalls - place where water flows over a vertical drop in the course of a stream or river

– Flood plains - a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge

Erosion

• Erosion of Earth’s Surface– Shaping Earth’s Surface

• Groundwater erosion– Groundwater can erode soft underground rock, such as

limestone, forming caverns

– Erosion of soft rock near the surface can lead to the formation of sinkholes, also known as karst formations.

Erosion

• Erosion of Earth’s Surface– Shaping Earth’s Surface

• Effects of water deposition– When water flowing downhill enters a valley, it may leave

behind deposits of sediment call alluvial fans.

– When streams and rivers enter oceans or lakes, the water slows and sediment is deposited, sometimes in seasonal layers. These large accumulations of sediment called deltas.

River delta

Source: earthobservatory.nasa.gov

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Water– Wave Erosion

» Waves and longshore currents often remove sand from beaches

» Sea arches, sea stacks, sea caves, and headlands may form as well

Erosion

• Erosion of Earth’s Surface– Agents of Erosion

• Water– Wave Deposition can create

» Beaches (at the edge of the water)

» Sandbars (in the water)

» Barrier islands (offshore)

» Spits (small projections of land)

Wave erosion – Sea arch

Source: schools.bcsd.com

Classwork 1 – Erosion

1. What are the four agents of erosion?

2. Describe the ways that gravity causes erosion

3. Describe the ways that water causes erosion

4. Describe the ways that ice causes erosion

5. Describe the ways that wind causes erosion

Copy the questions into your notebook (right-side) and answer them