The Earth's surface has been subjected to numerous changes and phenomena known as geological processes. Cliff erosion, a volcanic eruption, or sedimentation at a mouth of a river are examples of these geological processes. The geological agents responsible for these processes are: waves, the internal heat of the Earth, or rivers.
Geological agents and processes are classified as internal and external.
It can be said that internal geological processes build the Earth's relief.
Internal agents and processes tend to lift and build the Earth's relief from the interior. External agents and processes tend to destroy and shape the Earth's relief.
Although processes such as volcanic eruptions and earthquakes affect the Earth's surface, they clearly originate in the Earth's interior. Therefore, they are internal processes.
Both internal and external geological agents need a source of energy to drive them so that processes can take place.
The internal heat stored in the Earth is responsible for our planet being geologically active. The origin of this heat comes from two sources: most of it has been stored since the beginning of the Earth's formation resulting from the collision of the planetesimals. The rest is generated by the disintegration of radioactive elements.
This internal heat generates convection currents in the mantle, which behaves like an extremely thick liquid. When the materials in the interior heat up, they expand, become less dense and rise. As they cool, they descend and continue the cycle.
The average gradient on the continents is 30º C per km, although the values are higher in active volcanic areas and lower in old cratons.
External agents that shape the relief are driven by solar energy that arrives at the Earth's surface. This energy creates differences in temperature in air masses, causing winds. It also powers the water cycle as it permits the evaporation of large quantities of water from the oceans that fall on the continents in the form of rain or snow.
Gravity also has an important role in both external and internal geological processes. It contributes to the formation of convection currents in the Earth's interior, in which cold, dense materials sink and are replaced by hotter and lighter materials that rise. On the surface, gravity causes water and ice accumulated on the continents to move towards the sea, forming rivers and glaciers which erode and shape rocks along their courses. In addition, gravitational pull is responsible for one of the movements of the sea: the tides.
Activity 12
Observe the image and then answer the questions below.
Activity 13
Distinguish between geological agents and processes in the following list. Then classify them into external or internal.
Activity 14
Explain the role of gravity in the processes shown below.
Activity 15
What is the temperature at the base of the Earth’s crust, 30 km deep?
Activity 16
Explain how a glacier is moved by solar energy and gravity.
Activity 17
Why is the Earth active, with internal dynamics, while the Moon, Mercury or Mars are geologically dead?
