External Geological Agents1. WIND: can cause erosion, mass wasting and sedimentation The main erosion processes cause by wind are:

DEFLATION forms a layer of rocks that is called a desert pavement (stony field - reg).

ABRASION forms mushroom-shaped rocks

Aeolic sedimentation when wind finds an obstacle in the landscape

Sand dunes are formed (in sandy deserts (ergs))

Differents types of dunes: Barchan dunes

Star dunes

Transverse dunes

2. GLACIERS: are divided into an accumulation zone and an ablation (wastage) zone along an equilibrium line. Glaciers are made up ice and snow, water, rocks and sediments. A glacier moves very slowly (few centimeters to a few meters each day).

• There are different types of glaciers:Alpine glaciers: cirques, horns, arete , U-valley, moraines (lateral, medial,

end)

Continental glaciers: which are continuous masses of ice that are much larger than alpine glaciers. Small continental glaciers are called ice fields. Big continental glaciers are called ice sheets.

3. Wild water:

GREAT AMOUNT OF WATER

STREAMSSTREAMS ARE NON DEFINED NOR PERMANENT COURSES OF WATER

RAINSTORM MODIFY THE RELIEF

Smooth and homogeneous

SOIL

easily eroded

Heterogeneous SOIL

some parts are harder to erode

FAIRIES’ CHIMNEYS

RILL

GULLY

TORRENTS Intermittent , short water courses very steep slopesfixed channelice melts or a period of heavy rains.

• 4. RIVERS: • 0.0001% of the Earth's water . • Different sources: lakes , springs (from underground), rain or melting snow

and ice (high mountains)

To narrow river consider its drainage basin and its floodplain:drainage basin flood plain

Rivers (masswasting processes)

1.Early maturity V-shape valley

2. Late maturity. Flat-floored valley .Narrow flood plain. River begins to meander. Flood plain widens

3. Old age. Very wide flood plain. Cut-off meanders (ox-bow lakes)

Rivers (erosion) three valley shape.

• 5. Ground water• Groundwater : water in the ground is stored in the spaces between rock particles. • A groundwater aquifer is an underground layer that holds water within soil,

porous rock, or similar material. • A groundwater well may be used to extract water from a groundwater aquifer.

• Karst relieves are landscapes shaped by the dissolution of a soluble bedrock layer, (usually carbonate rock such as limestone or dolomite) by a mildly acidic water.

• These landscapes display different:• surface landforms (sinkholes, dolines, disappearing and reappearing streams,

poljes) • underground features (extensive caves and cavern systems may be formed. In

caves, the deposition of calicium carbonate may form stalactites, stalagmites, column)

SEA WATER

waves, tides, sea currents

erosion, transport, sedimentation processes

is constantly movinghas a lot of energy

•6. Sea water in coastal areas

THEY MODEL COASTAL AREAS

WAVES

Chemical Physical weathering

Erosion

Salty sea reacts in chemical ways with rocks and makes them weaker

Stones, other sediments are carried by waves and they crash into the coastal rocks.

Cliffs, sea caves, arches, abrasion platforms, sea stacks

LANDFORMS

WAVESTransport and sedimentation of materials

Beach: deposition of sand and gravel along the shoreline

Longshore drift: This process is when individual particles are moved along the beach in a zig-zag pattern

Longshore drift Spits, bay barrier, barrier island, tombolos, lagoons…LANFORMS

The sediments (sand, mud and pebbles) accumulate in sedimentary basins , forming layers or plies.

These layers of sediment are sinking deeper and deeper into the basins.

Under conditions of high temperatures and high pressures

The sediments become rock (lithified) through a process called DIAGENESIS (it may take millions of years)

SEDIMENTARY ROCKS

Clastic sedimentary rocks such as conglomerate, sandstones, shale .Chemical sedimentary rocks, such us halite, gypsum Organic sedimentary rocks such us limestone, coal.

Types of sedimentary rocks

CONGLOMERATE SANDSTONE SHALE

HALITE

COALLIMESTONE

GYPSUM