Changing the Earth's Surface - Globalization and Winesfmilmo.weebly.com/uploads/2/8/0/9/28096307/changing_the_earths_… · Changing the Earth’s Surface Weathering, Erosion and

Changing the Earth’s Surface

Weathering, Erosion and Deposition If you were to watch a rock, it would seem that

the rock never changes. But when rocks are

exposed on the Earth’s surface, processes

acting on the rock’s surface break it down into

smaller and smaller pieces called sediment. We

cannot always see this process, because in

some cases, it takes a very long

of time.

The process in which rocks are broken down is called

weathering. There are two types of weathering, physical

and chemical. Physical weathering changes rock without

changing its composition. Plant roots wedging into rock,

water freezing in rock cracks, and rock collisions all cause

rocks to break down.

Chemical weathering is a process in which the

chemical composition of the rock is changed. Gases

dissolved in water, such as weak acids and salts, act on

the rock to break them down into new substances.

Lichens, a fungus in a symbiotic relationship with algae,

produce acids which chemically can break down rock.

The process of erosion includes weathering of rock and the movement of

the sediment to other places. When the sediment reaches its final

destination, it is deposited and often forms a new layer of rock.

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TEKS 7.8B analyze the effects of weathering, erosion, and deposition on the environment in ecoregions of Texas TEKS 8.9C interpret topographic maps and satellite views to identify land and erosional features and predict how these

features may be reshaped by weathering

Rivers Most landscapes are formed by moving water. As the water collects down a

slope, it forms narrower and deeper channels. The water can erode the soil

to form gullies, valleys and canyons. Flowing

water can cut small channels a few centimeters

deep or great canyons the size of the Grand

Canyon.

Eroded sediment carried by the moving water

moves downhill and toward the ocean. The

sediment is deposited where the river enters a

body of water such as a lake or the ocean. This

area is called a delta.

Most rivers are curvy rather than straight.

Over time, the shape of a river changes

because the river shifts sideways in its

position. Rivers tend to erode one bank

and deposit sediment on the other bank. The river

valley eventually becomes wider and wider and the

river path much more curved. When the valley

becomes broad, almost like a flat plain, it is called a

floodplain. When the river floods, it spills over its

banks and floods the surrounding area. Fine sediment,

called silt, is deposited on the floodplain.

Waves Rivers aren’t the only places where moving water

shapes Earth’s surface. As ocean waves move

toward the shore, they deliver a tremendous

amount of energy. The waves hitting the shore

slowly wear away the rock material along the

shoreline. The wave action can create cliffs,

sea caves and sea arches.

Sand beaches are shaped by

the waves as well. The waves

carry grains of sand over

enormous distances. The

sand can be carried not only up and down the beach, but

along the beach! Over time, huge amounts of sand can be

moved along a beach.

To preserve beaches, engineers construct long wall structures such as jetties

and breakwater barriers. These structures protect shores and beaches, but

they often fail during an especially large storm.

Glaciers

A glacier is a large mass of ice on the Earth’s

surface. The ice in the glacier flows because of its

own weight and gravity. As it moves it scrapes the

surface of the Earth and carries rocks and

sediment along, carving a ‘U’ shaped valley.

Material pushed by the glacier forms a ridge of sediment called a moraine.

When the weather warms and the glacier begins to melt, streams of melt

water flow out from beneath the glacier. These streams carry glacial sand

and gravel for long distances before they deposit the sediment in river

valleys.

Wind In places where the wind blows, the wind causes

small particles of sediment to be lifted and carried

to other places. Sometimes the moving particles

encounter other rock materials or formations and

wear away the softer material. Unusual formations

are left behind.

Wind erosion often occurs where there is little or no

vegetation. An example is the formation of sand

dunes. Sand dunes are constantly moving. How

fast the dune moves depends on the speed of the

wind, size of the dune and how much vegetation is

present. Some dunes are stabilized because they

have plants growing on them that have extensive

root system. The roots help to hold the sand in place.

Time

If the process of erosion has been moving eroded rock from the continents

for long periods of time, why haven’t the continents been worn away? The

answer is that forces within the Earth also uplift the surface. So the

continents are continually being eroded

away, reformed and reshaped. Earth’s

surface looks very different from how it

did millions of years ago. The

processes of weathering, erosion and

deposition constantly recreate the

landscape over time.