How External Forces Shape the Landscape

The landscape around us changes due to the action of external forces acting on its surface. The main energy source is solar energy.

Landscape Transformation by External Forces

The Role of Solar Energy

The amount of solar energy varies with latitude: the sun's rays do not strike all points of the Earth's surface in the same way. The energy received decreases as a function of latitude from the equatorial zones towards the poles, producing a thermal imbalance which is compensated by the flow of energy in the form of heat. This heat propagates through convective cells and is responsible for:

• Maintaining appropriate conditions for the development of life in the biosphere.
• Causing wind, clouds, rain, and snow, forming rivers, torrents, valleys, and glaciers.
• Originating ocean currents, waves, and the evaporation of water in the hydrosphere, putting water in motion and giving rise to the water cycle.

Geomorphology: Study of Landforms

Geomorphology is the science of the forms of relief in a region and the processes that generate them. The main factors are:

• Climatic factors.
• Structural factors.
• Lithological factors.

Some of these often exert a greater influence.

External Geological Processes

The main external geological processes are:

1. Erosion: The breakage or wear suffered by rocks due to mechanical action. This includes:
   • Physical action: Physical separation of fragments.
   • Chemical action: Modification of the chemical components of rocks.
2. Transport: The fragments are moved to another area.
3. Sedimentation: The deposition of fragments in the lower areas of continents, seas, and oceans, which are called sedimentary basins. The accumulated deposits form layers called strata. These layers convert into sedimentary rocks through a process called lithification.
4. Weathering: The destruction of rocks by the action of the atmosphere. Weathering can be:
   • a) Physical: Physical disruption of rocks into increasingly smaller pieces. This occurs in hot, desert areas and high mountains. It can happen by:
     • Thermal expansion or differential fragmentation.
     • Fragmentation by frost or gelifraction.
     • Haloclasty.
     • Bioclasty.
   • b) Chemical: Due to chemical reactions between atmospheric components and minerals from the rock. The resulting products have a different chemical composition. This takes place in wet and equatorial climates. The main processes are:
     • Hydration.
     • Hydrolysis.
     • Dissolution.
     • Oxidation.
     • Carbonation.