erosion and deposition by flowing water

deposition by streams and rivers

When a stream or river slows down, it starts dropping its sediments. Larger sediments are dropped in steep areas, but smaller sediments can still be carried. Smaller sediments are dropped as the slope becomes less steep. Alluvial Fans In arid regions, a mountain stream may flow onto flatter land. The stream comes to a stop rapidly. The deposits form an alluvial fan, like the one in Figure 10.7. Deltas Deposition also occurs when a stream or river empties into a large body of still water. In this case, a delta forms. A delta is shaped like a triangle. It spreads out into the body of water. An example is shown in Figure 10.7.

textbook_image

deposition by flood waters

A flood occurs when a river overflows it banks. This might happen because of heavy rains. Floodplains As the water spreads out over the land, it slows down and drops its sediment. If a river floods often, the floodplain develops a thick layer of rich soil because of all the deposits. Thats why floodplains are usually good places for growing plants. For example, the Nile River in Egypt provides both water and thick sediments for raising crops in the middle of a sandy desert. Natural Levees A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the waters edge. You can see how levees form in Figure 10.8. Levees occur because floodwaters deposit their biggest sediments first when they overflow the rivers banks.

erosion and deposition by groundwater

Some water soaks into the ground. It travels down through tiny holes in soil. It seeps through cracks in rock. The water moves slowly, pulled deeper and deeper by gravity. Underground water can also erode and deposit material.

textbook_image

caves

As groundwater moves through rock, it dissolves minerals. Some rocks dissolve more easily than others. Over time, the water may dissolve large underground holes, or caves. Groundwater drips from the ceiling to the floor of a cave. This water is rich in dissolved minerals. When the minerals come out of solution, they are deposited. They build up on the ceiling of the cave to create formations called stalactites. A stalactite is a pointed, icicle-like mineral deposit that forms on the ceiling of a cave. They drip to the floor of the cave and harden to form stalagmites. A stalagmite is a more rounded mineral deposit that forms on the floor of a cave (Figure 10.9). Both types of formations grow in size as water keeps dripping and more minerals are deposited.

textbook_image

sinkholes

As erosion by groundwater continues, the ceiling of a cave may collapse. The rock and soil above it sink into the ground. This forms a sinkhole on the surface. You can see an example of a sinkhole in Figure 10.10. Some sinkholes are big enough to swallow vehicles and buildings.

textbook_image

erosion by slowflowing rivers

Rivers flowing over gentle slopes erode the sides of their channels more than the bottom. Large curves, called meanders, form because of erosion and deposition by the moving water. The curves are called meanders because they slowly wander over the land. You can see how this happens in Figure 10.6. As meanders erode from side to side, they create a floodplain. This is a broad, flat area on both sides of a river. Eventually, a meander may become cut off from the rest of the river. This forms an oxbow lake, like the one in Figure 10.6.

textbook_image

textbook_image

how a waterfall forms

Mountain streams may erode waterfalls. As shown in Figure 10.5, a waterfall forms where a stream flows from an area of harder to softer rock. The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step, creating a waterfall. As erosion continues, the waterfall gradually moves upstream.

erosion by mountain streams

Streams often start in mountains, where the land is very steep. You can see an example in Figure 10.4. A mountain stream flows very quickly because of the steep slope. This causes a lot of erosion and very little deposition. The rapidly falling water digs down into the stream bed and makes it deeper. It carves a narrow, V-shaped channel.

textbook_image

textbook_image

erosion by runoff

When a lot of rain falls in a short period of time, much of the water is unable to soak into the ground. Instead, it runs over the land. Gravity causes the water to flow from higher to lower ground. As the runoff flows, it may pick up loose material on the surface, such as bits of soil and sand. Runoff is likely to cause more erosion if the land is bare. Plants help hold the soil in place. The runoff water in Figure 10.3 is brown because it eroded soil from a bare, sloping field. Can you find evidence of erosion by runoff where you live? What should you look for? Much of the material eroded by runoff is carried into bodies of water, such as streams, rivers, ponds, lakes, or oceans. Runoff is an important cause of erosion. Thats because it occurs over so much of Earths surface.

erosion and deposition by surface water

Water that flows over Earths surface includes runoff, streams, and rivers. All these types of flowing water can cause erosion and deposition.

deposition by water

Flowing water slows down when it reaches flatter land or flows into a body of still water. What do you think happens then? The water starts dropping the particles it was carrying. As the water slows, it drops the largest particles first. The smallest particles settle out last.

particle size and erosion

The size of particles determines how they are carried by flowing water. This is illustrated in Figure 10.2. Minerals that dissolve in water form salts. The salts are carried in solution. They are mixed thoroughly with the water. Small particles, such as clay and silt, are carried in suspension. They are mixed throughout the water. These particles are not dissolved in the water. Somewhat bigger particles, such as sand, are moved by saltation. The particles move in little jumps near the stream bottom. They are nudged along by water and other particles. The biggest particles, including gravel and pebbles, are moved by traction. In this process, the particles roll or drag along the bottom of the water.

textbook_image

water speed and erosion

Faster-moving water has more energy. Therefore, it can carry larger particles. It can carry more particles. What causes water to move faster? The slope of the land over which the water flows is one factor. The steeper the slope, the faster the water flows. Another factor is the amount of water thats in the stream. Streams with a lot of water flow faster than streams that are nearly dry.

how flowing water causes erosion and deposition

Flowing water is a very important agent of erosion. Flowing water can erode rocks and soil. Water dissolves minerals from rocks and carries the ions. This process happens really slowly. But over millions of years, flowing water dissolves massive amounts of rock. Moving water also picks up and carries particles of soil and rock. The ability to erode is affected by the velocity, or speed, of the water. The size of the eroded particles depends on the velocity of the water. Eventually, the water deposits the materials. As water slows, larger particles are deposited. As the water slows even more, smaller particles are deposited. The graph in Figure 10.1 shows how water velocity and particle size influence erosion and deposition.

textbook_image

instructional diagrams

description_image

The diagram represents the coastal Erosion of a headland. A headland is an area of hard rock which sticks out into the sea. Headlands form in areas of alternating hard and soft rock. Where the soft rock erodes, bays are formed on either side of the headland. As the headland becomes more exposed to the wind and waves the rate of its erosion increases. When headlands erode they create distinct features such as caves, arches, stacks and stumps. The sequence in the erosion of a headland is as follows: 1. Waves attack a weakness in the headland. 2. A cave is formed. 3. Eventually the cave erodes through the headland to form an arch. 4. The roof of the arch collapses leaving a column of rock called a stack. 5. The stack collapses leaving a stump.

description_image

The diagram shows how a waterfall is formed by erosion. Waterfalls begin with mountain streams that begin high up in mountains. These streams flow down very quickly because of the steep slope, and flowing water, especially fast-moving water, erodes soil and rocks. Soft rock erodes more quickly than hard rock. When soft rock erodes, the stream bed can collapse, causing an abrupt drop in the stream. This sudden drop is what creates a waterfall. In the diagram, the overhang is where the stream bed collapsed to create the waterfall. Because of the flowing water, the soft rock at the side of the waterfall will continue to erode. This continued erosion will cause more of the stream bed to collapse. The waterfall overhang will then retreat upstream and create a higher waterfall.

questions

Flowing water can cause erosion by dissolving minerals in rocks.

-->  a. true

b. false

More slowly flowing water can carry larger sediments.

a. true

-->  b. false

The size of sediments determines how they are carried by flowing water.

-->  a. true

b. false

Clay and silt are carried in flowing water by suspension.

-->  a. true

b. false

Runoff is only a minor cause of soil erosion.

a. true

-->  b. false

Rapidly flowing mountain streams cause little deposition.

-->  a. true

b. false

Slowly flowing rivers erode their channels more at the bottom than at the sides.

a. true

-->  b. false

Floodplains are poor places for growing crops.

a. true

-->  b. false

A levee forms from the largest sediments a river carries.

-->  a. true

b. false

Sinkholes are caused by groundwater erosion.

-->  a. true

b. false

broad flat area on both sides of a river where it floods its banks

a. alluvial fan

b. delta

c. levee

-->  d. floodplain

e. cave

f. sinkhole

g. oxbow lake

underground hole or cavern eroded by groundwater

a. alluvial fan

b. delta

c. levee

d. floodplain

-->  e. cave

f. sinkhole

g. oxbow lake

deposit that forms when a mountain stream flows suddenly onto flatter land

-->  a. alluvial fan

b. delta

c. levee

d. floodplain

e. cave

f. sinkhole

g. oxbow lake

raised strip of sediments deposited along the bank of a river

a. alluvial fan

b. delta

-->  c. levee

d. floodplain

e. cave

f. sinkhole

g. oxbow lake

hole on the surface of the ground that forms when a cave collapses

a. alluvial fan

b. delta

c. levee

d. floodplain

e. cave

-->  f. sinkhole

g. oxbow lake

triangular deposit that forms when a river empties into a body of still water

a. alluvial fan

-->  b. delta

c. levee

d. floodplain

e. cave

f. sinkhole

g. oxbow lake

body of water that forms when a meander is cut off from the rest of the river

a. alluvial fan

b. delta

c. levee

d. floodplain

e. cave

f. sinkhole

-->  g. oxbow lake

Agents of erosion include

a. gravity.

b. waves.

c. ice.

-->  d. all of the above

Erosion is always followed by

-->  a. deposition.

b. weathering.

c. suspension.

d. saltation.

Factors that determine how much erosion runoff can cause include

a. how fast the water is moving.

b. how much water is flowing.

c. whether the land is bare or covered with plants.

-->  d. all of the above

A waterfall forms when a stream flows

a. from lower to higher elevations.

-->  b. from harder to softer rocks.

c. from one meander to another.

d. from side to side in its floodplain.

When flowing water slows down, which of the following sediments does it drop first?

-->  a. gravel

b. sand

c. silt

d. clay

Which statement about stalactites is false?

-->  a. They form on the floors of caves.

b. They consist of mineral deposits.

c. They look like icicles.

d. They grow slowly.

What forms when a river erodes the outside of a curve and deposits sediments on the inside of the curve?

a. delta

b. floodplain

-->  c. meander

d. sinkhole

diagram questions

question_image

How many actions are depicted in the diagram?

a. 6

b. 4

c. 8

-->  d. 7

question_image

How many steps are there to the formation of a stump?

a. 6

b. 5

c. 10

-->  d. 7

question_image

Which of these are most affected by a storm?

a. Dunes

b. Continental shelf

c. Shoreface

-->  d. Intertidal beach

question_image

In a storm beach, what is exposed during the low tide?

a. High tide

-->  b. Rocks

c. Upper beach

d. Dunes

question_image

Where is eroded intertidal beach sediment deposited in a storm weather beach system?

a. On the dunes

-->  b. On the lower shoreface

c. On the upper beach

d. On the continental shelf

question_image

In which step does the cliff collapse?

a. 4

b. 2

-->  c. 3

d. 1

question_image

Which step is the cause of the erosion process shown?

a. 4. Cliff retreats

-->  b. 2. Wave-cut notch

c. 5. Wave-cut platform

d. 1. Original position of cliff

question_image

What happens before cliff retreats?

a. Wave-cut platform

b. Wave-cut notch

c. Nothing

-->  d. Notch increases and cliff collapses

question_image

What is located just below the wave-cut notch?

a. Notch increases and cliff colapses

b. Cliff retreats

c. Origiinal position of cliff

-->  d. Wave-cut platform

question_image

What is the area of water where the river falls called?

a. river

b. lake

-->  c. Plunge pool

d. waterfallretreats

question_image

How many types of rocks are shown in the diagram?

a. 2

b. 1

c. 4

-->  d. 3

question_image

What collapses and creates a fall?

a. plunge pool

-->  b. overhang

c. pebbles and stones

d. soft rock

question_image

Which label points to undercutting?

a. 1

b. Top left

c. Bottom middle

-->  d. 3

question_image

What forms when a sea cave is eroded through completely?

a. Blowhole

-->  b. Arch

c. Stump

d. Stack

question_image

In this diagram of Erosion and Deposition by Flowing Water, what is located just below the Headland?

a. Stump

b. Blowhole

-->  c. Arch

d. Stack

question_image

What material is deposited on the slip off slope?

a. soil

b. fine material

-->  c. sand and shingle

d. rocks

question_image

Where does the sand deposits?

a. In the air

-->  b. In the river

c. In the soil

d. In the cliff

question_image

What is deposited on inside of bend?

-->  a. Sand and Shingle

b. Current

c. River cliff

d. Slope

question_image

Why is flowing water important agent of corrosion?

-->  a. Flowing water can erode rocks and soil

b. it maintains the water

c. it keeps the soil dry

d. it keeps the soil firm

question_image

What happens to rock after weathering?

a. rain will cause the rock to expand

-->  b. Erosion from rain will cause the sediments to go downhill

c. no effect

d. rain will cement the sediments on the hill surface

question_image

What causes the sediments to move downhill to another place?

-->  a. Erosion and transport

b. Weathering

c. Precipitation

d. Condensation

question_image

What rock formation causes rapids?

a. Soft Rocks

b. Fallen Rocks

c. Overhang

-->  d. Hard Rock

question_image

Which is the name of the exact point where water falls in a waterfall?

-->  a. Overhang

b. Hard rock

c. Steep-sided gorge

d. Plunge pool

question_image

How many ridges of hard rock are shown in this picture?

a. 3

b. 5

-->  c. 2

d. 4

question_image

How are rapids created?

a. overhang

b. fallen rocks

-->  c. Ridges of hard rick create an uneven slope

d. waterfall retreats

question_image

Which of the bottom labels (numbered from left to right) points to low tide?

a. 1

b. 4

-->  c. 2

d. 3

question_image

How many phases of the tide are there?

a. 3

-->  b. 2

c. 4

d. 1

question_image

In this diagram of Erosion and Deposition by Flowing Water, where does the water go through the blow hole?

a. Arch

b. High Tide

-->  c. Caves

d. Stump Covered at High Tide

question_image

What is the first stage in the formation of waterfall?

a. overhang collapses

b. plunge pool develops

-->  c. undercutting

d. waterfall retreats upstream

question_image

How many formations of a waterfall are there?

a. 4

-->  b. 5

c. 3

d. 2

question_image

What is shown in the picture?

a. Photosynthesis

b. Life Cycle

-->  c. Erosion and Deposition by Flowing Water

d. Solar Heat

question_image

What is located in a plunge pool?

a. Hard rock

b. A waterfall

-->  c. Fallen rocks

d. Fish

question_image

What prominent feature develops when a waterfall retreats?

-->  a. Steep sided gorge

b. fallen focks

c. overhang

d. plunge pool

question_image

What happens when stream flows from an area of harder to softer rock?

a. Erosion occurs.

-->  b. A waterfall forms.

c. A plunge pool forms

d. A lake forms

question_image

What is the part over the plunge pool called?

a. fallen rocks

b. rapids

-->  c. overhang

d. gorge

question_image

How many types of rock are in the picture?

a. 5

b. 4

-->  c. 2

d. 3

question_image

What is under hard rock?

a. Water

-->  b. Soft rock

c. Nothing

d. Stream

question_image

What is the empty space behind the falling water in this drawing?

a. hard rock

-->  b. undercutting

c. Soft Rock

d. cave