Chapter 7: Erosion and Deposition

7.1: Forces wear down and build up Earth’s surface7.2: Moving water shapes land

7.3: Waves and wind shape land7.4: Glaciers carve land and move sediments

7.2 Moving water shapes land

Before, you learned:Erosion is the movement of rock and soilGravity causes mass movements of rock and

soilNow, you will learn:

How moving water shapes Earth’s surfaceHow water moving under ground forms caves

and other features

Streams shape Earth’s surface

Think about a river: Surrounding land is higher than the riverSteep valley: see the river is the low pointEven in very flat places, land is sloping down to the

river, which is running downhill through the landWater running downhill changes the land:

Shapes landforms by moving sediment in the processes of erosion and deposition

Water can carve out new features underground

Drainage Basins and Divides

Where does water go when it rains or ice melts on a slope?Soaks in the ground flows down the slope in thin sheetsBecomes part of a channel that forms a streamStream: any body of water that flows down a slope

along a channelStreams flow into one another to form complex

drainage systemsSmall flow into largerDrainage Basin: area of land in which water drains into

a stream systemWater usually eventually drains into a lake or ocean

Drainage Basins and Divides

Drainage basins are separated by ridges called dividesA ridge from which water drains to one side or

the otherCan be along a mountain, or simply the highest

line of landAre boarders of drainage basins

The Continental Divide

Runs from Alaska to Mexico

Most water that falls west: drains to the Pacific Ocean

Most water that falls east: drains into the Gulf of Mexico or the Atlantic Ocean

Valleys and Floodplains As streams flow and carry away sediment, they form valleys In high mountains they often cut V-shaped valleys that are narrow

and steepwalled In low areas, they may form broad valleys that include floodplains

An area of land on either side of a stream that is underwater when the stream floodsCan make the land very fertile when it deposits sediments

Stream Channels

Meanders: twisting and looping pattern in a stream channelErodes the outside

banks and deposits sediment along the inside banks

A flood can cause a new channel to form, cutting off the meander into a crescent-shaped lake: oxbow lake

Alluvial Fans and DeltasStreams also create landforms

called alluvial fans and deltas, formed by deposition of sedimentAlluvial fan: fan-shaped deposit of

sediment at the base of a mountain Forms where a stream leaves a steep

valley and enters a flatter plainStream slows down and spreads out,

depositing sediment

Delta: area of land formed by the buildup of sediment at the end, or mouth, of a riverWhen the river enters the ocean, it slows,

depositing sediment• Sediment gradually builds up to form a plain

Water moving underground forms caverns

Some rainwater runs into surface streams, some evaporates, some is absorbed by plants…and some soaks into the ground and becomes groundwater

Deep below, spaces in soil and rock become completely filled with waterThe top of this region is called the “water table”Below the water table is “groundwater”Can change with rainfall

Groundwater

Can cause erosion deep below where it slowly flows through underground beds of rock and soil

Rainwater is slightly acidic and can dissolve certain rocks, such as limestone

The groundwater can dissolve some of the limestone and carry it away Can form caves Large caves = caverns If the water table drops, the cavern can be filled with air

Cavern System of passageways, containing lakes and streams Sinkhole: a basin that forms when the roof of a cave becomes so

thin that it suddenly falls inPossibly because water that supported the roof drained away

http://www.pbs.org/wnet/nature/lessons/breaking-it-down/video-segments-violent-hawaii/1702/ - hawaii

http://www.youtube.com/watch?v=IR6evrt7els - bill nye

http://dsc.discovery.com/videos/planet-earth-caves-limestone-erosion.html

http://dsc.discovery.com/videos/earth-live-rain-and-floods/

http://www.cbsnews.com/video/watch/?id=3440105n