ESO 4 B & G 8

The Earth's External Energy

What to Learn

  • The external geomorphological changes vs. the internal geomorphological changes: paces and examples.
  • The Sun and the gravity as the causes behind the external geomorphological agents. The water cycle as an example.
  • The external geomorphological processes: weathering, erosion, transport and sedimentation.
  • Chemical weathering.
  • Geomorphological action of the changes of temperature. Freeze-thaw weathering.
  • Geomorphological action of the wind. Occurrence, aeolian landscapes.
  • Geomorphological action of the superficial continental waters. Types of superficial continental bodies. The geomorphological processes in the sections of a river. Glacial vs. fluvial landscapes.
  • Geomorphological action of the subterranean continental waters. Karstic landscapes.
  • Geomorphological action of the sea. Seawater movements. Landscapes carved by the sea movements.
  • The formation of soils.
  • The formation of sedimentary rocks. Strata.
  • Fossilisation.

Key Information

Geological agentAny agent able to alter the surface of our planet.
External geological agentGeological agents powered by the Sun or the Earth's gravity: the water flows (streams, torrents, rivers, glaciers), the sea, the wind, the atmospheric phenomena (rainfall, thunderstorms, cyclones), the temperature variations or the living beings.
Weathering / ErosionWeathering is the decomposition of rocks, soils and their minerals through the action of some of the external geological agents. It is called erosion when the decomposing agent also transports the resulting fragments away.
ClastsThey are the resulting rock grains of the weathering process. They are classified upon their size as follows: clay (< 0.004 mm), silt (< 0.06 mm), sand (< 2 mm), gravel (< 6 cm), cobbles (< 25 cm) and boulders (> 25 cm).
Frost shatteringOr freeze-thaw weathering. It's a kind of physical weathering usually produced by the expansion of the water filling the cracks in the rocks of the mountain areas where the daily temperature variation is around 0°C. The nightly pieces (wedges) of ice thus formed exert a pressure in the cracks called ice-wedging.
GullyLandform that resembles a series of sharp and very short channels carved by intermittent running water, usually by streams, and typically formed on deforestated hillsides.
RavineDeep, narrow and short channel with steep sides, carved by intermittent running water, usually by torrents. Bigger than gullies and smaller than valleys.
Canyon / GorgeAn extreme type of V-shaped valley: narrow, deep and with very steep sides (cliffs), carved by running water, usually by rivers. If the sides are stepped, reflecting alternating rock resistances, it is called a canyon; otherwise it is a gorge.