Relief

ch videos and take notes.

http://www.youtube.com/watch?v=kNc8NTiisUM&feature=related

http://www.youtube.com/watch?v=JTgbjLMwUEM&feature=relmfu

 (landforms parts 1 and 2)

http://www.youtube.com/watch?v=i3c3t3bi2aI&feature=endscreen&NR=1 landforms definitions.

Make a mind map with concepts from videos.

http://www.youtube.com/watch?v=Y7EO4ygqyIU&feature=autoplay&list=PLF9293CDDD9E49786&playnext=2 (erosion)

On maps locate (draw) the main world and Mexico´s relief.

RELIEF

The relief (or terrain) is the different shapes that the surface of the Earth has adopted over millions of years. It can divided into continental (surface relief) and oceanic (submarine relief).

The relief is the result of internal internal forces, which form it and external forces, which transform it.

CONTINENTAL RELIEF

•Mountains: elevations of the terrain above the surrounding land with steep slopes or sides and an altitude of more than 600 metres. When they are together in “rows” they are knows as sierras or mountain ranges, as the Himalayas (Asia), that is the world’s highest one.

•Valleys: are areas of low land between mountains. Rivers flow through many valleys.

•Plains: low, flat areas of land., no higher than 200 metres above sea level. They are formed by large rivers.

•Plateaus: large plains raised more than 200 metres above sea level. The highest plateaus are the Tibetan High Plateau (Asia) and the Bolivian (South America).

•Basins (or depressions): sunken or drepressed areas below the surrounding areas. Some are below sea level .

 

COASTAL RELIEF

Coastal relief: coasts are where the continents meet oceans and seas. The coastal relief forms are:

•Peninsula: an area of land surrounded by water on all sides except one.

•Isthmus: connects a peninsula to a continent.

•Cape: part of the coast which extends into the sea

•Gulf: a large area of sea or ocean partially enclosed by land. A bay is a small gulf

•Island: an area of land surrounded by water on all sides

•Archipelago: is a group of islands

•Beaches: flat coastal area with sand or stones.

•Cliffs: high coastal area with steep rock formations.

•Estuary: area formed when the sea flows into de mouth of a river

•Fiord: strip of sea that comes into the valley of a river / land between high cliffs.

 

OCEANIC RELIEF

• Continental shelf: is the extension of the continents under the seas or oceans. They are vast plateaus which reach a depth of 150-200 metres.

•Continental slope: is a steep incline found between the continental shelf and the abyssal plain.

•Abyssal plains: are large flat areas of the deep ocean floor (4,000 or 5,000 metres below sea level). In them we can find:

•Oceanic ridges: large mountain ranges that rise up 3000 metres from the ocean floor. Some of the highest peaks rise above the surface and form islands such as the Hawaiian Islands.

• Oceanic trenches: are large, deep depressions in the ocean floor. The deepest one is the Challenger Deep (11000 metres) in the pacific Ocean.

HOW THE RELIEF IS FORMED?

Continental drift

In 1912 Alfred Wegener developed the continental drift theory. According to it, there was only one continent, which broke up millions of years ago. This continent was called Pangea

Tectonic plates

The Earth’s crust is divided into different plates called tectonic plates. They are in continous movement (speed of two to ten centimeters per year).

Some plates from move apart letting the magma come out. Some other plates collide, creating folds when the terrain is flexible or faults when it is extremely rigid. Also, the collison of plates has produced many mountains, such as the Himalayas range which is still rising.

The movement of tectonic plates can produce volcanoes and earthquakes:

•A volcano is an opening in the surface of the Earth through which very hot rocks, magma comes out. When magma is outside the volcano it is called lava. Volcanoes are generally found on the edge of tectonic p lates.

•Earthquakes are also caused by plate tectonics; when two plates crash, the ground vibrates. This vibration is called an earthquake. When the crashing is on the ocean floor the earthquake can produce waves called tsunamis.

HOW IS THE RELIEF TRANSFORMED?

External forces shape the relief. This transformation involves three types of action:

• Erosion: is the fragmentation and dissolution of rocks, soil and mud.

• Transportation: eroded materials are transported by wind or water.

• Sedimentation: is the accumulation of sediments such as mud, sand or mud.

 

There are four main agents of erosion: temperature, water, wind and living things.

 

1. Temperature: abrupt changes in it can break rocks. It happens in mountains or deserts, where there is a great difference between daytime and night time temperatures.

2. Water:

◦ When it infiltrates through rocks and freezes, water expands and breaks the rocks.

◦ Solution is when water dissolves some kinds of rocks, such as limestone producing caves.

◦ Fluvial erosion: In the upper course the river erodes materials creating deep valleys and canyons/ In the middle course the slopes are gentler and rivers transport the eroded materials/ In the lower course, near the sea, land is flat and water deposit sediments on the river´s banks forming alluvial. plains.

◦ Marine erosion: waves and currents wear away coasts creating cliffs. Sediments transported by the sea water are deposited and form beaches.

3. Wind: transports particles of sand or soil from their original place and deposites them. Sand dunes are formed this way.

4. Living things: Plants and animals transform the relief through their activities./ Human beings make the fastest and more dangerous impact through activities such as farming, mining, deforestation, building roads, tunnels or reservoirs.