1.11 Coastlines and Erosion

8/12/2019 1.11 Coastlines and Erosion

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Coastlines (Pinggir

Laut/Pantai)

Coast, geographical term that refers to the zone of contact between a land

surface and a large body of water.

The term is usually applied to a land area that borders a sea or an ocean,such as the Atlantic coast or the Pacific coast.

In common usage, the term coastis frequently interchanged with the term

shore. Howeer, shoreis also applied to the land bordering smaller bodies of

water such as a la!e shore, where use of the term coast would be

inappropriate.

outline of coast: the outline of a coast as iewed from the sea or on a

map

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Erosion

#rosion, remoal of roc! and soil material by natural processes, principally

running water, glaciers, waes, and wind.

#rosion transports roc!y material after the process of weathering has bro!en

bedroc! down into smaller, moeable pieces.

Through erosion the surface of the earth is constantly being sculptured into new

forms.

The shapes of continents are continuously changing, as waes and tides cut into

old land while silt from riers builds up new land.

As riulets, streams, and riers cut their channels deeper, gullies become raines

and raines become alleys. The $rand Canyon, more than "%&& m 'more than

%&&& ft( deep, was produced by erosion probably within the past % million years.

The oerall effect of the wearing down of mountains and plateaus is to leel the

land) the tendency is toward the reduction of all land surfaces to sea leel. *or

e+ample, in each &&&- to &&&-year period the entire area drained by the

/ississippi 0ier loses an aerage of 1& cm '"2 in( of altitude. 3pposing this

tendency are olcanic eruptions and moements of the crust of the earth thatraise mountains, plateaus, and new islands. See $eology) $eomorphology 2


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Weathering

4eathering initiates the erosion of roc!, causing alterations in the surface layers.In dry climates, the top layer of a roc! may e+pand from the heat of the sun and

crac! off from the lower layers. If the roc! consists of seeral minerals, the

minerals may e+pand at different rates and brea! up the roc!. In cold climates,

frost brea!s up roc!s because rainwater, which seeps into crac!s and pores in the

roc!, e+pands when it freezes. 0ain in damp climates acts chemically as well as

mechanically in the weathering of roc!s. As the rain passes through theatmosphere it absorbs carbon dio+ide, forming carbonic acid, which dissoles

some minerals and decomposes others. *eldspar, a common family of minerals in

granite, is changed into clays, and certain minerals in basalt combine with o+ygen

and water to form iron o+ides, such as limonite. Plants play a role in weathering

as roots can split roc!s and e+tract soluble nutrients.

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Water Erosion

4ater plays an important role in erosion by carrying away material that hasbeen weathered and bro!en down. 4hen an area receies more water 'in

the form of rain, melting snow, or ice( than the ground can absorb, the

e+cess water flows to the lowest leel, carrying loose material with it. $entle

slopes are sub5ect to sheetand rillerosion, in which the runoff remoes a

thin layer of topsoil without leaing isible traces on the eroded surface.

This erosion may be balanced by the formation of new soil. 3ften, howeer,especially in arid areas haing little egetation, the runoff leaes a pattern

of gullies formed by riulets. 4ater can een erode solid roc!, especially

along streambeds where the stones that are carried with the current scour

and abrade. #ery year riers deposit about 1.% million tons of eroded

material into the oceans.

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Glacial

Erosion

$laciers are important agents of erosion. Although a glacier moes slowly, itgradually remoes all the loose material from the surface oer which it

traels, leaing bare roc! surfaces when the ice melts. 7esides remoing

loose material, glaciers actiely erode the solid roc! oer which they trael.

0oc! fragments that become embedded in the bottom and sides of the

moing ice mass act as an abrasie, grinding and scouring the bedroc! which

forms the walls and floors of mountain alleys.

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Wind Erosion

4ind is another actie agent of erosion, especially in arid climates with littleegetation. 4ind blowing across bare land lifts particles of sand and silt but leaes

behind larger pebbles and cobbles. #entually, a surface layer of closely pac!ed

stones, called a desert paement, is formed as the sand and silt is remoed. The

remoal of large quantities of loose material is called deflation. 8eflation lowers the

landscape slowly, usually less than a meter '1 ft( in a thousand years. Howeer,

deflation can occur more rapidly, as it did during the "1&s in the southern parts ofthe $reat Plains of the 9nited :tates 'see 8ust 7owl(. 4inds may sometimes

deposit sand in large piles, !nown as sand dunes.

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Coastal

Erosion

Coastal erosion of roc!y cliffs and sandy beaches results from the action of

ocean waes and currents. This is especially seere during storms. In many

parts of the world the loss of land due to coastal erosion represents a

serious problem. The action of waes, howeer, does not e+tend to a great

depth, and the sea tends to cut a flat platform, characteristic of marine

erosion, into coastal roc!s.


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Human Impacts On Erosion

4ithout human actiities, losses of soil through erosion would in most areas

probably be balanced by the formation of new soil. 3n irgin land a mantle of

egetation protects the soil. 4hen rain falls on a surface of grass or on the

leaes of trees, some of the moisture eaporates before it can reach the

ground. Trees and grass sere as windbrea!s, and a networ! of roots helps to

hold the soil in place against the action of both rain and wind. Agriculture andlumbering, as well as housing, industrial deelopment, and highway

construction, howeer, partially or wholly destroy the protectie canopy of

egetation and greatly speed up erosion of certain !inds of soils. #rosion is

less seere with crops such as wheat, which coer the ground eenly, than

with crops such as corn and tobacco, grown in rows.

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1.11 Coastlines and Erosion