Erosional Forces

Erosion

• Wearing away of surface materials by gravity, water, wind, or glaciers.

• Deposition- process where sediments are dropped by erosion agents as they lose energy.

• Mass movement occurs as gravity moves materials down a slope as one large mass.• Examples: Slumping, Creeping, Rock

Falls/Slides, & Mudflows

Steep slopes can be made safer with vegetation, drainage pipes, and walls of concrete or railroad ties.

Glaciers

• Large masses of ice and snow that slowly move on land causing erosion.

• Plucking- erosion process caused by moving glaciers picking up boulders, gravel, & sand.

• Scour & scrape the soil and bedrock.

• Grooves & striations indicate the direction a glacier moved.

•Glaciers deposit a mixture of different sized sediments (till) when they retreat.oMoraine- a ridge, or pile, of deposit left at the end of a glacier.oOutwash- material deposited in layers by the meltwater of a glacier, with largest pieces closer to the glacier..oEskers – outwash deposit formed as meltwater rivers within the ice deposit sand & gravel within their channels.

Zone of AccumulationZone of Accumulation

Zone of WastageZone of Wastage

CrevassesCrevasses

SnowlineSnowline

• Types of GlaciersContinental Glaciers-huge masses of ice

and snow that cover large areas of land.

•Covers 10% of Earth near the poles. (Antarctica & Greenland)

• Ice Ages - periods of widespread glaciation over the last 2 to 3 million yrs.

•Thicker than some mountain ranges.

Valley Glaciers- exist in mountain ranges.

• Cirques- bowl-shaped basins in the sides of mountains.

• Arête- a long ridge that forms when two valley glaciers erode a mountain side-by-side.

• Peaks- form when valley glaciers erode a mountain from several directions.

• Valleys formed by glaciers are “U” shaped

The

Wind

• Scatters dust or volcanic ash over thousands of kilometers.

• Deflation- wind removes small particles of loose sediment, leaving behind heavier materials.

• Abrasion- wind behaves like a sandblaster blowing sand grains against rocks wearing them down.

• Windbreaks – rows of trees planted to slow down wind in order to reduce erosion.

• Dunes – mounds of sediment drifted by wind.

Water Erosion

Surface WaterRunoff• Rainwater that doesn’t soak in to the

ground or evaporate.• Affected by:

Amount of rainfall Length of time it falls Steepness, or slope, of the land Amount of vegetation

Rivers & Streams

• River system –network of groundwater & streams that come together to form a system.

• Drainage Basin- area of land from which a stream or river collects runoff. The Mississippi River drainage basin is

the largest in the United States

Young River Flows swiftly through a narrow

valley. May have rapids & waterfalls. Erodes the bottom faster than the

sides. “V” shaped valleys

Mature Stream Flows smoothly through the valley. Erodes more on the sides. Forms meanders & oxbow lakes. Carves a flat, broad valley floor

called a floodplain.

Old Stream Flows smoothly through a floodplain it

has carved.

meandersmeanders

oxbow lakeoxbow lake

flood plainflood plain

valley wallvalley wall

• Delta – fan shaped area formed by sediments that are deposited as water empties into an ocean or lake.

• Alluvial Fan – fan shaped area formed by sediments that are deposited as water empties from a mountain valley onto a flat open plain.

Groundwater• Groundwater is water that soaks into the

ground and collects in the pores of the underlying soil.

• Soil and rock are permeable if water can pass through the pore spaces. (Sandstone)

• Soil and rock are impermeable if water can not pass through the pore spaces. (Granite)

• Aquifer – a layer of permeable rock that lets water move freely. Zone of Saturation : area where all the

pores are filled with water. Water Table : upper surface of the zone

of saturation.

Zone of Zone of AerationAeration

Water TableWater Table Zone of Zone of SaturationSaturation

AquiferAquifer

Thethe

•Wells are used to pump groundwater from an aquifer to the surface.Artesian wells – wells that don’t require a

pump because the water is under pressure.Spring – free flowing water because the

water table is so close to the surface.Geyser – hot spring that erupts peroidically,

shooting water & steam into the air.

• Caverns are formed by Carbonic acid dissolving limestone rock, thereby enlarging cracks to form chambers.Stalactites– Calcium carbonate deposits

that hang from a cave’s ceiling.Stalagmites – Calcium carbonate deposits

that form on a cave’s floor.

Other Features:Other Features:

Cave PopcornCave Popcorn

Soda StrawsSoda Straws

Cave PearlsCave Pearls

ColumnsColumns

DraperiesDraperies

Ocean Shoreline Shoreline Forces– Waves pound

against pound against shores.

– Currents move sediments along the shoreline.

– Tides carry sediment out to sea & bring in new sediment.

Rocky Shorelines Rocks & cliffs

C. Sandy Beaches Beaches –deposits of sediments

parallel to the shore. Barrier Islands – fragile sand deposits

that parallel the shore but are separated from the mainland.