Erosion and Deposition

Erosion Sediment -natural forces move rock/soil from one place to another. -gravity, water, wind, glaciers, waves are causes -material moved by erosion

Deposition -when erosion lays down sediments -works with weathering & erosion -involved in wear down and build up of Earth’s surface -never ending cycle

Water Erosion Runoff & Erosion Runoff -major agent of erosion: moving water -all remaining water on Earth’s surface -may cause sheet erosion (thin layer over land)

Rills Gullies -tiny grooves in the soil -large groove, or channel, in soil that carries runoff -only flow after it rains -may dry up

Streams Rivers -channel where water constantly flows down a slope -rarely dries up -also called creeks or brooks -a large stream

Amount of runoff -depends on 5 factors: 1. amount of rain in an area 2. vegetation: grasses, shrubs, trees reduce runoff 3. type of soil 4. shape of the land: steep land has more runoff than flatter 5. how people use the land -more runoff = more erosion

River Systems Tributary Drainage Basin -stream that flows into a larger stream -ex. small creek that flows into a large river is a tributary to that river -land area where a river and its tributaries collect water

Divide Erosion by Rivers -high ground between two drainage basins -ex. Continental Divide -rivers create: valleys, waterfalls, flood plains, meanders, & oxbow lakes

V-Shaped Valleys Waterfalls -form when rivers erode along steep slopes -occurs when river meets an area of rock that is hard & erodes slowly

Flood plains Meanders Oxbow lake -flat, wide area of land along a river -looplike bend in a river (snake-like) -meander that has been cut off from a river (u-shape) -may form when a river floods

Deposits by Rivers Alluvial Fan -deposition creates: alluvial fans & deltas -can also add soil to a river’s flood plain -wide, sloping deposit of sediment formed where a stream leaves a mountain range -shaped like a fan

Delta -landform made of sediment deposited where a river flows into an ocean or lake

Groundwater Erosion & Deposition -water soaks into ground when it rains -underground water -affects the shape of the land -causes erosion through chemical weathering -combines with carbon dioxide to form a weak acid = carbonic acid -weathers limestone -forms deposits from roof/floor of caves

Stalactite Stalagmite Karst Topography -deposit on roof of cave -cone-shaped deposit on floor of cave -landscape where limestone is near the surface -characterized by caverns, sinkholes, and valleys

Glaciers Glacier -large mass of ice that moves slowly over land -two types: valley (alpine) and continental

Valley/Alpine Glacier Continental Glacier -long, narrow -forms when snow/ice build up high in mountain valley -usually move down valleys cut by rivers -covers much of a continent or large island -much larger than valley -covers 10% of Earth’s land - Antarctica & Greenland

Ice Ages -continental glaciers covered large parts of Earth’s surface -last ice age lasted 70,000 years and ended 10,000 years ago

How glaciers form & move -only form in area where more snow falls than melts -snow builds year after year -pressure on bottom layers turns snow into ice -valley g. flow a few cm to m each day -continental flow in all directions

Glacial Erosion Plucking -two processes: plucking and abrasion -as glacier flows, it picks up rocks -weight of ice breaks rock -carries rocks as it moves

Abrasion Deposition -gouges, scratches bedrock as glacier drags rocks -glacier melts, deposits sediment eroded from land -creates landforms

Till Moraine -deposits directly on surface -many different sized particles -ridge formed when till is deposited at edge of glacier -ex. Long Island in New York

Kettle -small depression that forms when ice is left in till -ice melts, kettle remains -often fills with water forming ponds/lakes -ex. the Great Lakes

Waves How waves form -waves get energy from blowing wind -energy causes water particles to move up and down -water particles don’t move forward -only form of the wave moves -as waves approach shore, it drags on the bottom -friction causes waves to slow

-major erosion force along coasts -erode land by impact Erosion by Waves -major erosion force along coasts -erode land by impact -large waves hit with great force -breaks apart rock -also erode by abrasion -sediment picked up by wave -wears rock like sandpaper -energy of wave depends on headland -part of shore that sticks out -harder rock; resists waves

Landforms -waves hit same area over and over -erodes base of land along steep coasts -places of soft rock form sea caves -also forms sea arches; pillar of rock above water

Deposits -waves shape coast thru erosion & deposition -as waves slow, they drop sediment -similar to river deposition -forms beaches

Beach -area of wave-washed sediment along coast -usually sand -comes from rivers that flow into ocean -some are coral/shells piled up

Longshore Drift Spit -movement of sediment caused by waves hitting shore at angles -forms a spit -beach that projects like a finger into water

Wind How Wind Causes Erosion -weakest agent of erosion -effective in deserts

Deflation -process by which wind removes surface materials -main way wind causes erosion -stronger the wind, larger the particles that can be picked up -doesn’t usually greatly effect land -creates areas of rock fragment called desert pavement -produces bowl-shaped hollows called blowouts -abrasion polishes rock

Deposits from wind erosion Sand Dunes Loess -forms: sand dunes & loess deposits -deposit of windblown sand -different shapes & sizes -can move over time -fine, wind-deposited sediment -helps to form fertile soil

Gravity Mass Movement Force that moves rock downhill. -caused by gravity -different types: *Landslides *Mudslides *Slump *Creep

Landslides Mudflow -rock/soil slide quickly down a slope -rapid downhill movement of water, rock/soil -occurs after heavy rains in a dry area

Slump Creep -mass of rock/soil slips down a slope -occurs when water soaks the base of a mass rich in clay -slow downhill movement of rock/soil -often results from freezing/thawing