Streams play an important role in erosion. The stream banks collapse in mass movement. The soil is then carried away by the stream as sediment. - PowerPoint PPT Presentation

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Streams play an important role in erosion. The stream banks collapse in mass movement. The soil is then carried away by the stream as sediment.

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Streams play an important role in erosion. The stream banks collapse in mass movement. The soil is then carried away by the stream as sediment. – PowerPoint PPT presentation

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Title: Streams play an important role in erosion. The stream banks collapse in mass movement. The soil is then carried away by the stream as sediment.


1
  • Streams play an important role in erosion. The
    stream banks collapse in mass movement. The soil
    is then carried away by the stream as sediment.

2
  • The primary force of erosion is gravity, which
    pulls sediment and water downhill.
  • Deposition is the process in which sediment is
    laid down in new locations.
  • Most sediment is moved and deposited by flowing
    water.

3
Running Water Erodes the Land
4
Running Water Erodes the Land
  • Erosion begins when runoff carries small
    particles of soil downhill.
  • Runoff forms small channels in the soil.
  • Channels join together to form gullies.
  • Gullies flow together to form streams.

5
Running Water Erodes the Land
  • Most of the sediment in streams is carried in
    suspension, in which tiny sediment grains move
    along with the water.
  • Larger particles of sediment slide, roll, or
    bounce along the bottom of a stream. The process
    of particles bouncing along a stream bottom is
    called saltation.
  • A large amount of sediment is also carried in
    solution.

6
Running Water Erodes the Land
  • The water in a mountain stream moves quickly
    because it is flowing down a steep slope.
  • Fast streams carry more sediment, which causes
    more abrasion.
  • Fast streams can also carry large sediment
    grains.
  • As a stream flows toward the sea, its slope
    decreases, and larger sediments settle on the
    stream bottom.

7
Running Water Erodes the Land
  • Streams continue the process of erosion by
    transporting sediment.

Direction of flow
8
Features Formed by Water Erosion
9
Features Formed by Water Erosion
  • V-Shaped Valleys
  • Near a streams source, the stream flows fast
    down steep slopes.
  • Mass movement on the stream slopes causes a
    V-shaped valley with sharply angled sides to
    form.
  • A waterfall may develop where a stream crosses
    rock layers that differ in hardness.

10
Features Formed by Water Erosion
  • As a river winds its way from the mountains to
    the ocean, it changes the surrounding landscape
    through erosion and deposition.

Waterfall
V-shaped valley
Meander
Oxbow lake
Sediment
River mouth
11
Features Formed by Water Erosion
  • Flood Plains
  • Where a river or stream crosses gently sloping
    land, it forms a flood plain, a flat area along a
    stream that is entirely covered only during times
    of flood.
  • Sediment builds up into long, low ridges called
    natural levees, which help prevent a river from
    spilling over its banks.

12
Features Formed by Water Erosion
  • At a curve in a river, the water on the outside
    of the curve moves more rapidly than the water on
    the inside and causes more erosion.
  • Sediment is deposited on the inside of the curve,
    where water moves more slowly.
  • This process forms a looplike bend in the river
    called a meander.

13
Features Formed by Water Erosion
  • Sometimes during a flood, the river erodes
    through a narrow neck of land at the base of a
    meander and forms a new path.
  • Sediments build up and cut the old meander off
    from the rest of the river.
  • The result is a separate, curved lake, called an
    oxbow lake.

14
Features Formed by Water Erosion
  • Rivers often form winding meanders and oxbow
    lakes across their flood plain.

15
Features Formed by Water Deposition
16
Features Formed by Water Deposition
  • Deposition is the process in which sediment is
    laid down in new locations. As a stream flows out
    of the mountains and onto the plains, it slows
    down and sediment settles out.
  • An alluvial fan is a fan-shaped deposit of
    sediment on land. Alluvial fans often grow into
    thick deposits of sediment.
  • A delta is a mass of sediment deposited where a
    river enters a large body of water.

17
Features Formed by Water Deposition
  1. This alluvial fan in Death Valley, California,
    formed from sediment deposited when a mountain
    stream reached flat land.
  2. When a large river empties into the ocean, the
    deposited sediment often forms a delta.

18
Groundwater Erosion
19
Groundwater Erosion
  • Erosion and deposition occur below ground as well
    as at the surface.
  • Carbon dioxide in the air combines with rainwater
    to form carbonic acid, which reacts with some
    rocks.

20
Groundwater Erosion
  • Limestone easily erodes away through this
    process, forming caves, or caverns.
  • Caves usually form in the saturated zone, below
    the water table. When the water table drops, it
    leaves dry caves.

21
Groundwater Erosion
  • Sometimes water drips into the cavern from the
    rock layers above, carrying dissolved minerals
    that are left behind when carbon dioxide escapes
    from the water.
  • Water dripping from the ceiling forms a
    stalactite.
  • Water dripping to the floor forms a stalagmite.

22
Groundwater Erosion
  • If erosion weakens a layer of limestone, entire
    portions of the ground can suddenly collapse.
  • The resulting hole is called a sinkhole.
    Sinkholes can appear suddenly, swallowing
    buildings and roads.

23
Groundwater Erosion
  • Carlsbad Caverns in New Mexico contain
    spectacular formations, such as the stalactites
    and stalagmites shown here.

24
Assessment Questions
  • What is the most important factor in determining
    a streams ability to cause erosion?
  • width of the stream
  • depth of the stream
  • composition of the water
  • speed of the stream

25
Assessment Questions
  • What is the most important factor in determining
    a streams ability to cause erosion?
  • width of the stream
  • depth of the stream
  • composition of the water
  • speed of the streamANS D

26
Assessment Questions
  • Which feature is most likely to form near the
    source of a river?
  • meander
  • flood plain
  • V-shaped valley
  • alluvial fan

27
Assessment Questions
  • Which feature is most likely to form near the
    source of a river?
  • meander
  • flood plain
  • V-shaped valley
  • alluvial fanANS C

28
Assessment Questions
  • Caves and sinkholes are geological features that
    are generally found where the bedrock consists of
  • granite.
  • quartzite.
  • sandstone.
  • limestone.

29
Assessment Questions
  • Caves and sinkholes are geological features that
    are generally found where the bedrock consists of
  • granite.
  • quartzite.
  • sandstone.
  • limestone.ANS D
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