action of external agents in relief final students

7/25/2019 Action of External Agents in Relief Final Students

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Unit 9

THE ACTION OF EXTERNAL

AGENTS ON RELIEF

IES Val Mior

Seccin Europea

Biology & Geology 3 ESO


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1. THE GEOLOGICAL ACTION OF WATER

Water acts in various ways:

- as surface runoff (escorrenta superficial)

- washes (torrentes)

- rivers

- seas (waves, tides and ocean currents)

- underground streams (correntes subterrneas)


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1.1 SURFACE RUNOFF

- Water flows freely without following an established course

- Its action is more intense:

- on steep slopes (pendentes pronunciadas)- when rain is torrential

- when the substrate is formed by soft rock or deep soil

- where there are no plants to protect the soil

- The effects of surface runoff are more noticeable in regions withsubdesert climates. There are not very many plants there andrain is torrential

- The ground is covered with furrow (surcos), which increase insize until they become gullies (crcavas). This kind oflandscape is called badlands (paisaxes ridos con crcavas)


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1.2 WASHES (torrente)

- Sporadic water channels with a established course whichappear where a steep slope suddenly ends in a flat area

- Washes have 3 sections:

- receiving basin (conca de recepcin)

- natural channel (canal de desaugadoiro)

- alluvial fan (abano aluvial)


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1.2 WASHES (torrente)

receiving basin (conca de recepcin)

natural channel

(canal de desaugadoiro)

alluvial fan (abano aluvial)


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1.3 RIVERS

- They have a high capacity for erosion and transport

- They sort the materials they carry by particle size

- The longitudinal profile of a river:1. Upstream section

2. Middle section

3. Downstream section


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1.3 RIVERS

Rivers sort the materials they carry by particle size


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An oxbow lake is a U-shaped body

of water formed when a widemeander from the main stream of ariver is cut off to create a lake

(lago de media la)


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1.3 RIVERS

1. Upstream section- the slope is steep

- the water flows quickly and is very erosive

- the water creates V-shaped valley and gorges (ravines or canyon)


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1.3 RIVERS

1. Upstream section: gorges (ravines or canyon)

Desfiladero de los Gaitanes, Mlaga

Desfiladero de Mont-rebei,

Pirineo cataln


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1.3 RIVERS

2-3. Middle to downstream section

- the slope become less pronounced

- the water flows less quickly- the water begins to deposit some of the load it is carrying

(from the largest to the finest particles)

- the valley becomes wider and flatter at the bottom (trough-

shaped valley)- because of the lower speed of the current, the river channel

forms meanders


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1.3 RIVERS

2-3. Middle to downstream section

Notice the deposits on the

inside banks of meanders.

Trough-shaped valley: valle del Ceze,Francia


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1.3 RIVERS

(chaira de inundacin)

Flood plain: plain that borders ariver, formed from sedimentdeposited by flood; it is an areaof great fertility


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River mouth (where the river flows into the sea)

A) DELTAS

- They are formed by deposits of sediments as the river enterthe sea

B) ESTUARIES- The sea enters the downstream section of the river, because

the river does not carry much sediments or flows into thesea with strong current capable of redistributing the

sediments


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1.4 THE SEA

The action of the sea on relief produces coastal landforms

(cabo)

(cala)(acantilado)

(marisma deauga salobre)

(punta)


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1.4 THE SEA

COASTAL EROSION

- When rocks are heterogeneous, they have different resistanceto erosion and the coastal landscape has headlands, bays and

coves

- When there are homogeneous rocks, the coastline is straight

The most typical landform of coastal erosion are cliffs


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- The erosion of a cliff is greatest at its base where large waves break andthey undercut the foot of the cliff, forming a wave-cut notch

- This undercutting continues and the overhanging cliff collapses downwards

- This erosive process continues and the cliff gradually retreats and becomessteeper.

- As the cliff retreats, a rocky platform is left at the base, this is known as awave-cut platform which is exposed at low tide


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1.4 THE SEA COASTAL DEPOSITION

- When the waves deposit the sediments they are carrying,beaches and sandbars are formed. As these sandy depositsgrow, they can close a bay off from the open sea (lagoon,laguna), or they can join an island to the coast (tombolo)

- The sediments depositaround a river mouths

can form a coastalmarshes (marisma) (flatareas with channelswhere sea water enters

the land and leaves it)


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1.5 UNDERGROUND WATER (KARST LANDFORMS)

Karst landforms are produced as a result of the dissolutionprocess when water is trapped in soluble rocks, like salts,

gypsum (xeso) and limestone (caliza)

Karst landforms can be:

- surface landform- underground landform


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Surface karst landform

Limestone pavement (lapiaz) are created bywater flowing over the surface of the rock anddissolving it

Sinkholes (dolina) are more or less circulardepressions; swallow holes (sumidero) where astream disappears underground

Poljes are very large depressions


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Underground karst landform

Potholes (sima) are vertical underground caves

Caves are horizontal and contain passages, caverns andchambers


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1.5 UNDERGROUND WATER (KARST LANDFORMS)

There are different kinds of underground formations producedby precipitation of calcium carbonate contained in drippingwater:

Stalactites: developed oncave ceiling

Stalagmites: developedon cave floors

Columns: formed whenstalactites and stalagmites

join together


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2. THE GEOLOGICAL ACTION OF ICE

- Glaciers are enormous bodies of ice formed bycompacted snow. Gravity causes them to flow to areaswhere they melt

- Ice sheets or continental glaciers are huge areas ofglaciers in Antartic and Greenland which can beseveral kilometers thick

- Alpine or valley glaciers are found in mountain areasof temperate climate


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- Huge capacity to erode and transport material

They are capable of excavating deep valleys and oftransporting blocks of rocks of hundreds of meters

- Glaciers do not smooth the sediments they carry orseparated them by size. The sediments are deposited inlinear mounds called moraines

Depending on their position,moraines can be classified aslateral, medial, ground or

terminal moraines

THE CHARACTRERISTICS OF GLACIERS


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Existen varios tipos de morrena segundo a sa relacin c glaciar:

Morrena de fondo: sitase baixo o xeo, en contacto c leito

Morrena lateral: os derrubios sitanse nas beiras do leito glaciar

Morrena central: formadas pola unin de morrenas laterais na

confluencia de dous glaciares nun mismo val

Morrena frontal ou terminal: depsitos de derrubios na zona de

desxeo do glaciar


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EROSION LANDFORMS

These include cirques, U-shapped valley, horn (picos piramidaisagudos) and tarn (lago pequeno de montaa).

Circo glaciar: conca en forma

de anfiteatro situada nacabeceira dun val glaciar

action of external agents in relief final students

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