Natural Science .

8/3/2019 Natural Science .

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EROSION ANDDEPOSITION



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Erosion@The break-up of rocks by the action of

rock particles beingcarried over the

earth’s surface bywaves, wind, and ice.



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DepositionThe p

rocess bywhich

sediments arelaid in new



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GRAVITY – Gravity pulls rocks

and soil down slopes.

MASS WASTING – Downwardmotion of sediments caused by

gravity.

LANDSLIDE – is the rumbling of

soil, rocks, and boulders down aslope.

MUDFLOW – illustrates rapid mass



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ROCK SLUMP – third example of mass wasting. This happens

when a rock resistant toweathering is over a layer of weak rock.

EARTH FLOWS – usually happenwhen heavy rain moves masses

of soil and plants slowly down aslope.

SOIL CREP – slowest kind of mass



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WIND•In deserts, beaches andplowed fields, the mostactive agent of erosion.Wind picks up and carries

loose materials likesand,silt,clay and dust

w/c are exposed on the’



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RUNNING WATER

Major cause of erosion. Itchanges more of the earth’s

surface than any otheragent of erosion.

n-off is the water that flows on

th’s surface after a rainfal



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RILLS Gravity makes water and

sediments move down will, cutinto the soil, and form many

tiny grooves.

GULLIES Act as channels for

run-off.



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HOW A RIVER SYSTEM DEVELOPS ?

As mentioned earlier, run-offs from rills. Rills

deepen and widen to form gullies. Gullies jointo form streams, streams join to form rivers.Rivers begin in mountains or hills. Gravity pullswater down and gives it energy to cut away

land and form valleys. The network of rills,gullies, and streams that from a river is calleda drainage system. How do the branches of atree compare with drainage system? The headof a river is in a mountain; its end or mouth is a

bigger river, lake or ocean. The head of thePasig River is in the mountains of Laguna andRizal, and its mouth is in Manila Bay. Its bodyflows from Laguna de Bay through Rizal

Province, and Manila.



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CAGAYAN RIVER – the longest river in the Philippines.

Three Longest River on Earth ;• Nile River in Africa• Amazon River of South America• Mississippi of North America

Life cycle of ariver: GradationAbout 3/8 of the total rain that falls on land returns to the seas

by stream run-off. It is the most important agent of erosion that

reduces land areas to lower levels. About 36,800 cubickilometers of water carried by streams supply energy for landerosion. The amount of run-off is determined by the slope of theriver, porosity and degree of saturation of rocks, character andamount of vegetation, removal of forests, humidity of regionsand dryness of the wind that blows.



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Methods of Stream

ErosionRivers remove products of weathering bycorrosion, and hydraulicking. By corrosion,river beds are worn off by impact and frictionof silt, sand, gravel and boulders carried by

rivers. They grind, rub and make rocks strikeagainst rocks. By corrosion, river waterdissolves minerals and carries theseimpurities that make them butter solvents.

About 5 million metric tons of solid materialsare carried into the sea. By hydraulicking,stream water scours out loose materials bycurrents passing over them, by the force of

collision of flowing water against a stream



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Transportation By RunningWater



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Source of Load

• Load carried by melting glacialice towards seas

•

Dust and ashes thrown fromvolcanoes into air and fallen intorivers or carried by rivulets into

them during rainfall collision of driftwood or blocks of ice on wallsof channels, uprooted trees,

animals and plants.



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How Materials are Transported

• Rivers transport their loads bypushing and dragging angular pieces

• Rolling rounded pebbles among theirfloors

• Carrying fine grains of sand, silt, andclay

• Dissolving and carrying solutions of soluble compounds.



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The greater the slope and amountof load, the greater the

transporting power of streams.

The greater the velocity, thegreater the carrying power of

water.



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Cycle of Stream Erosion



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rivers may be classified as young,mature, and old.

These describe the appearance andactivities going on, not their actual

ages.

Some parts of rivers and valleys maybe young, mature and old in term of

age and activity.

Steep sloped and narrow youngvalleys are found in upland regions

occupying most of the area.

Maturity means a balance of more



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Old valleys are boarder andgentler, and high landsalmost disappear; flat

valleys and land dominatethe region. Is your region

young, mature or old?

narro an eep s reams



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narrow, an eep s reamsthat dissect the area. This

upland area is dominantlyflat or rolling and has verylittle slope. Many streams

develop, new tributaries areadded, gullies grow into

brooks. The region is curvedinto hills, upland surface

disappears, slope dominate,



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At old age, flat bottom landsdominate the area and hillsbecome slightly rolling

divides that separate themain stream. Occasional

hard rocks stand out assmall hills or monad rocks.



4/27/12 Young valley



4/27/12 Mature Valley



4/27/12 Old Valley



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FEATURES YOUTH Torrent Stage

MATURITYValley Stage

OLD AGEPlain Stage

Shape of cross-section

V-shaped,deep, narrow

Open U-shapedbroad, well-

defined

Flat, with lowboundaries

Valley gradient steep Gradual,uniform

Very low, wider

Valley depth Moderately steep anddeep

Deepest Shallow

Velocity of flow Rapid Slower Very slow,sluggish

Load Very little Plenty Very heavy

Materialtransported

Coarse and fine Sand, silt,plenty

Silt & solutionpre-dominant

Down –cuttingwork

Fast Decreased Almost none,ended

Riverbed Close to earth’s surface Deepened Raised

Nature of divide Wide, low to high High andnarrow

Low andnarrow

Flood plain None or just starting Wide, welldeveloped

Very wide,rejuvenated,

Course of channel Straight Meandering Many meanders,



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Course of channel Straight Meandering Many meanders,oxbow lakes formed

Rapids, falls Plenty Few left, worn away Receded, filled up

Number of lakes Many on upland Few, if any Many on lowlands

Tributaries Few, small Many Few, large

Kind of erosiondominant

Vertical, down-cutting prominent

Horizontal, lateralplanation

Depositiondominant

Pot holes Plenty Filled up Flattened

Main feature Interlocking spurs River bends common,spurs removed

Natural levees

Relief Maximum forentire drainage

system

Maximum for regionof had waters

Low

Deposition bystreams

Minimumdeposition

Deposition at insideof curve

Deposition inchannels and on

levees

General drainage Poorly developed Well drained, mostefficient

Sluggish drainage

Adjustment of Not adjusted Well-adjusted Little affected by

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