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1. Internal geological processes
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2.1.
The engine of internal and external geological
processes
Both internal and external geological agents need a source of energy to drive them
so that processes can take place.
2.1.1.
The Earth’s internal heat
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.
Geothermal gradient
is defined as the increase of temperature with depth. It
is one of the most obvious indications of the Earth’s internal heat.
The role of gravity in the external processes
Understand
14.
Explain the role of gravity in processes shown above.
Key concepts
❚❚
Relief is the result of internal
and external geological
processes.
❚❚
Internal heat is the engine
of the geological processes,
while solar energy powers
external processes. In both
cases, the role of gravity is
decisive.
Diagram of convection currents
Understand
15.
What is the temperature
at the base of the Earth’s
crust 30 km deep?
Analyse
16.
Explain how a glacier is
moved by solar energy
and gravity.
17.
Why is the Earth active,
with internal dynamics,
while the Moon, Mercury
or Mars are geologically
dead?
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.
2.1.2.
Solar energy
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.
2.1.3.
Gravity
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.
