Unit 7:  External dynamics of the Earth                                     1   2   3

1. Landforms and relief

The relief is the shape of the Earth’s surface. Earth’s crust is not uniform and smooth but irregular and rough. Mountains, valleys, cliffs or plains are some of these irregularities which receive the general name of landforms. So that the relief is the join of the landforms of a territory.

This relief is constantly changing and it is consequence of the balance between two types of forces: internal and external.

a) Internal geological agents.

    Internal geological agents are responsible for the construction the relief.

They are due to the internal heat of the Earth.

The internal temperature and pressure of the planet increase with the depth. This provokes that rocks melt and change propelling the internal dynamics of the Earth.

b) External geological agents.

External geological agents are responsible for the destruction of the relief.

They are due to energy from the Sun and to the gravity.

They are the wind, the water (in whatever form), the atmosphere and the living beings. 

                    - Solar energy is the origin of:

                  - The water cycle. Water precipitates and running over the surface

          of the Earth shaping it.

                      - The dynamics of the atmosphere. The differences in temperature

           between air masses provoke the wind.

          - Gravity provokes the falling of the water and the loose materials.

These geological agents act simultaneously, so that the relief is build and destroyed at the same time. Their actions are the geological processes.

Geological processes are constantly shaping the Earth’s surface. The result is the different types of landforms that we can find all around the world.

1.1. Land relief

The emerged parts of the Earth, that is to say the parts not covered by sea water, consist of continents and islands. The most important features of this relief are: 

- Mountain ranges. Longitudinal groups of mountains spread over a large area.

- Plains. Large flat regions that form the most part of the continents.

1.2. Ocean floor relief

It constitutes approximately three quarters parts of the Earth’s surface. It is covered by the sea water.

The main characteristic features of this relief are: 

        - Continental shelf. These are submerged, flat extensions of continents,

          about 200m in depth. The platform ends in a steep slope called

          the continental slope.

- Abyssal plains. They are large plain more than 3,000 m deep. They start at the continental shelf and are the largest part of the ocean floor. The plain is interrupted by submerged mountains and volcanoes which sometimes are so high that emerge forming islands.

- Ridges. They are large underwater volcanic mountain ranges. They are thousands of kilometers long and divide the abyssal plain. They may be 2,000m high from the bottom of the ocean floor. There are cracks in their centre, called rifts that run along the entire length of the ridge.

- Trenches. They are very deep, narrow, long depressions which appear in some areas of the ocean floor. Some of them are more than 10 km deep and hundreds of kilometres long.

1.1. Answer these questions

       a. What is the origin of wind?

       b. What geological roll plays gravity?

       c. Which are the sources of energy that propel the geological agents?

       d. Why is the Earth’s relief constantly changing?

1.2. What are the differences between internal and external geological

        agents?

1.3. Indicate which relief’s feature refers each sentence:

      a. Large underwater volcanic elevation located in the middle of an ocean.

      b. Large groups of mountains in the continent.

      c. Part of a continent covered by the sea that reaches a depth of around 200 m.

      d. Flat extensive area on the deep ocean floor at more than 2,000m in depth.

      e. Very deep depression in the ocean floor.

      f. Flat extensive regions located in the middle of continents

      g. Deep fissure in the middle of the ocean ridge

      h. Area with big slope that connect the abyssal plain with the continental shelf.