chapter 7: erosion and deposition 7.1: forces wear down and build up earth’s surface 7.2: moving...
TRANSCRIPT
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
soil
Now, 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 land
Water 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