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.
3Running Water Erodes the Land
4Running 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.
5Running 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.
6Running 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.
7Running Water Erodes the Land
- Streams continue the process of erosion by
transporting sediment.
Direction of flow
8Features Formed by Water Erosion
9Features 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.
10Features 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
11Features 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.
12Features 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.
13Features 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.
14Features Formed by Water Erosion
- Rivers often form winding meanders and oxbow
lakes across their flood plain.
15Features Formed by Water Deposition
16Features 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.
17Features Formed by Water Deposition
- This alluvial fan in Death Valley, California,
formed from sediment deposited when a mountain
stream reached flat land. - When a large river empties into the ocean, the
deposited sediment often forms a delta.
18Groundwater Erosion
19Groundwater 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.
20Groundwater 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.
21Groundwater 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.
22Groundwater 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.
23Groundwater Erosion
- Carlsbad Caverns in New Mexico contain
spectacular formations, such as the stalactites
and stalagmites shown here.
24Assessment 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
25Assessment 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
26Assessment Questions
- Which feature is most likely to form near the
source of a river? - meander
- flood plain
- V-shaped valley
- alluvial fan
27Assessment Questions
- Which feature is most likely to form near the
source of a river? - meander
- flood plain
- V-shaped valley
- alluvial fanANS C
28Assessment Questions
- Caves and sinkholes are geological features that
are generally found where the bedrock consists of
- granite.
- quartzite.
- sandstone.
- limestone.
29Assessment Questions
- Caves and sinkholes are geological features that
are generally found where the bedrock consists of
- granite.
- quartzite.
- sandstone.
- limestone.ANS D