Weathering, Erosion and Deposition.(3rd/4th grade teach)
Weathering, Erosion and Deposition By Moira Whitehouse PhD
The Earth’s surface is constantly changing.Mount St Helens before and after it erupted in 1980.
New land is constantly being formed.Volcanoes erupt.Forces deep inthe Earth pushup chains ofmountains.
Land is being constantly worn down by wind,water and ice. original level of the plateau.
Weathering• The breaking down of rock into smaller and smaller pieces.
Some things in nature that cause weatheringWater in cracks in the rock freezing andexpandingPlant roots growing into rocksWater running over rocks, causing therocks to hit one another and break intosmaller piecesWind carrying sand that wears away rockCarbon dioxide dissolved in water formingan acid that eats holes in the rock
Water in cracks in the rock freezes.As it freezes it expands causing the rocks to break.
Expanding water as itwedgingslowly breaks up this Frost Action or ice freezes slowly breaks up this sedimentary rock into unusual shapes. rock into unusual shapes.
Weathering by glaciersA glacier is a large, river of ice thatmoves very slowly downhill.Glaciers are formedover many years aslarge amounts of snowfall and accumulate.The snow compactsand changes to ice. Stuck in the bottom of the glacier are stones of various sizes that wear away the rock under the glacier as it moves downhill.
Striations or scratches made in the rockunder a glacier by the stones stuck in it asthe glacier moved downhill.
Carbon dioxide that dissolves in water weathers rock• CO2 dissolves in rain water and creates carbonic acid• Carbonic acid easily weathers limestone making holes in the rock
ErosionThe process by whichwater, ice, wind orgravity moves piecesof rock and soil.When rock isweathered (brokeninto smaller andsmaller pieces), thesepieces are oftencarried away by water,wind or ice.
Water ErosionRivers, streams, and runoff carry weatheredrock or soil to another place.
Fast movingstreams andrivers carry bigand smallrocksdownstream.
Slower moving water carries smaller rocksand soil downstream.
Moving water can also cause soil erosion—carrying the soil away to a different location.
Sometimes a side of the hill is washed awayby running water. The soil and rocks movedown the hill in a landslide.
Canyons This simple animation provides you with a visualization of how the Colorado River has "downcut" into the rock layers of the Grand Canyon. Canyons demonstrate both weathering—the breaking down of rock into smaller pices and Canyons are large erosion—these pieces of rockvalleys created by a being moved to a new location. river or stream.
Wind ErosionStrong winds can move small rocks and soil fromone location to another.
Ice ErosionGlaciers moving overrocks breaks them downinto smaller pieces(weathering) and carriesthem away (erosion).
DepositionWhen the water slows down orstops movingWhen the wind dies down or stopsblowingWhen the glacier meltsthe rocks that the water, wind orglacier were carrying are dropped ordeposited in a new location.
Delta—water depositionWhere a river meets the ocean is called themouth of the river. Soil carried by a river isdeposited at the mouth and new land is formed.This new soil-rich land is known as a delta.
Wind DepositionSand dunes are large deposits of sanddropped when the wind stopped blowing. Thelocation of the sand dunes shifts frequently.
Glacial DepositionWhen glaciers melt, they drop or deposit the rocksthey were carrying.A moraine is therocks and soil leftbehind by a meltingglacier. Glacierspick up rocks anddirt that travel alongwith the glacier untilit eventually meltsand is left behind astill.
Although we talk about weathering, erosion anddeposition as three separate processes, they oftenoccur together. Over time, rocks are generally brokeninto smaller pieces (weathering) carried downhill(erosion) and deposited in a new location (deposition).
Do you remember the agents of weatheringthat we discussed?moving water in water in cracks in rocksstreams and rivers freezing and expanding glaciers plant roots windDo you remember the agents of erosion thatwe discussed? moving water in glaciers wind streams and rivers