Chp 8.2 Erosion and Deposition

The Geologic Cycle

• Erosion is the process by which natural forces move weathered rock and soil from one place to another.

• The material moved by erosion is sediment.

• When the agents of erosion lay down sediment, deposition occurs.

5 Agents of Erosion

GravityRunning waterWavesRain

GlaciersWind

Agent # 1: Gravity- Mass Wasting

• Mass wasting:– Is a form of erosion caused mainly by gravity.– Commonly occurs when the ground becomes

soaked with rainwater.– When the weight becomes too great, the mass of

soil will begin to slide.– Can occur from vibration from earthquakes, heavy

machinery, blasting

Landslides

• mass wasting that occurs when rock and soil slide rapidly down a steep slope.

Mudslides / Mudflows• A mudflow is the rapid downhill movement of a mixture of water, rock,

and soil. The amount of water in a mudflow can be as high as 60 percent.

Slump & Soil Creep• A slump is a type of mass movement in which a mass of rock and soil

rapidly slips down a slope. It looks as if someone pulled the bottom out from under part of the slope.

• Creep is the very slow downhill movement of rock and soil. It occurs most often on gentle slopes.

Agent #2: Running Water

• Precipitation can do any of 3 things:– Evaporate or Soak-in

or RUN OFF !• Water running downhill is

the major agent of erosion that has shaped Earth's land surface.

• Amount of runoff affected by: – Amount of Rainfall, Plant

Population, Shape of the land, Soil saturation

• Climate & Erosion – Areas that receive large amounts of precipitations,

are more likely to experience mass wasting.– Also there is more vegetation• Prevent landslides because the roots of plants help to

hold sediments in place.

Water & Erosion

• Stages of Stream Development– Rivers change as water

moves from the mountains down to lakes or oceans.

– Steep slopes allow the water to flow downhill rapidly.

• Development of Meanders

• Meanders are curves in the stream.

• The curves tends to become wider and wider.

• Deposition occurs inside the meander.

• Erosion occurs outside of the meander.

Stream Development

• Flooding– Occurs when the water

level in a river rises above the usual height and overflows the sides of its banks.

– Floodplain• Is a wide, flat valley that is

located along the sides of some rivers and streams.

Agent #3: Waves• Waves shape the coast through

erosion by breaking down rock and transporting sand and other sediment.

• Beach: is a landform consisting of loose sand and gravel.

• Cliff: formed by the cutting action of waves at the base of rocks that are exposed along the coasts.– When large waves hit the

shore, their energy can break apart rocks.

• The Longshore Curren– Waves come in at an

angle.– The waves bend until

they are approximately parallel to the coast.

– They retreat from the beach perpendicular to the shore.

– Most great amount of sediment along coasts.

Agent #4: Wind Erosion• Wind is the weakest agent of erosion.• Sand dunes: when heavier sediments that blows along the

ground surface and it is pushed into piles.• Loess: windblown silt that was carried in the air.

Agent #5: Glaciers• Glaciers: large masses of ice and snow, moving 2.5

cm per day.• There are two kinds of glaciers continental glaciers

and valley glaciers.– Plucking - As a glacier flows over the land, it picks up &

pushes rocks along w/ it.• The rocks trapped under the glacier create scratches.

– Till: builds along the sides and fronts of glaciers called moraines.

– Outwash: consists mostly of sand and gravel.

Continental Glaciers• Today, found only on Antarctica & Greenland• Covered most of North America & Europe during past Ice Ages• Able to flow in all directions.

Valley GlaciersWhen a glacier melts, it deposits the sediment it eroded from the land, creating various landforms.The mixture of sediments that a glacier deposits directly on the surface is called till.