LAND RELIEF, COASTAL LANDFORMS AND THE OCEAN FLOOR

Land Relief, coastal landforms and the ocean floor

The Earth's surface is very varied. It has relief features in the form of mountains, valleys and plains. Moreover, in coastal areas, the action of the sea shapes the relief to form beaches and cliffs. At the bottom of the ocean, there are also different relief features, just like on the surface of the continents.

Continental relief

The relief features we see today are the result of processes that began million of years ago. It was formed by two kinds of forces:

·         The Earth's internal forces: the movement of plates, volcanic eruptions, etc.

·         External agents: wind, rain, rivers, groundwater, lakes, ice, seas, oceans and living things (including human beings).

The Earth's internal forces created the relief, while external agents eroded the relief.

           

Continental relief includes several elements:

·         Mountains are very high elevations of the Earth's surface. They are sometimes grouped together in mountain ranges.

·         Plateaus are high flat areas that are formed from eroded mountains.

·         Plains are low flat areas. The sediments that have been deposited on plains often make them fertile for agriculture. Alluvial plains are formed by rivers. Coastal plains are near the sea.

·         Basin is very low areas. Some basins are below sea level.

           

Continental waters

These are located on the continents and can be freshwater (rivers, glaciers, groundwater and lakes) or saltwater (inland seas).

Rivers, glaciers and groundwater

           

·         Rivers flow from high ground along a river bed into the sea, a lake or another river. When one river flows into another, we call it a tributary.

§  Rivers are created by the accumulation of rainwater, melted snow and ice from mountains and springs.

§  Rivers and their tributaries form a fluvial system. The surface the flow across is a drainage basin.

§  The amount of water carried by the river is called the volume. This increases during the rainy seasons and falls during the dry periods.

·         A glacier is a large mass of ice that forms at the top of mountains and moves like a river.

·     Groundwater is created by the filtration of water from rain, rivers or streams through permeable, porous rock. When a layer of impermeable rock blocks the water, ground deposits called aquifers are formed.

Inland lakes and seas

A lake is a permanent accumulation of freshwater in a sunken area of land. A pond is a small lake. An inland sea is big and contains saltwater.

The size of inland lakes and seas depends on the area of sunken land and the amount of water that accumulates from rain, rivers and groundwater.

COASTAL LANDFORMS AND THE OCEAN FLOOR

Coastal landforms include beaches, gulfs, bays, fjords, capes, and cliffs.

Relief on the ocean floor

At the bottom of the ocean, we find the following relief features: continental shelf, abyssal plain, ocean trenches, ocean ridge and continental slope.

·         A continental shelf is a submerged plain, which is an underwater extension of a continent. In most cases, it extends to a depth of 200 m, but in some cases it can reach 500 m.

·         An abyssal plain is a large expanse of land at the bottom of the ocean at around 5500 m deep. Here we find trenches (long sunken areas) and ocean ridges (underwater mountain ranges).

·         The continental slope is the incline from the continental platform down to the abyssal plain. It can be up to 3600 m deep.

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