Earth’s Processes: Tectonics, Weathering, and Landforms
Earth’s Internal and External Processes
Folds are produced when a material undergoes plastic deformation due to compressive forces. They can be classified as antiform or synform. Geological processes can be external or internal.
External Geological Processes
External processes include weathering, erosion, transport, and sedimentation, caused directly or indirectly by solar energy. Diagenesis is also an external process.
- Weathering: The alteration of rocks by the action of air, water, or living things.
- Erosion: The removal and mobilization of rock fragments.
- Transport: The transfer of sediments to sedimentary basins.
- Sedimentation: The deposition of materials transported by ice, water, or wind.
Internal Geological Processes
Internal processes include magmatism and metamorphism. They are caused by the Earth’s internal heat.
Factors influencing internal processes:
- Temperature Increase: Presence of radioactive substances or contact with a heat source.
- Pressure Decrease: Reduces the melting point of the rock.
- Presence of Fluids: Also reduces the melting temperature of rocks.
Metamorphism: Occurs where rocks undergo changes in their mineral composition or texture.
- Isochemical Metamorphism: The overall chemical composition remains basically unchanged.
- Contact Metamorphism: Caused by temperature increase.
- Regional Metamorphism: Caused by an increase in temperature and pressure.
- High-Pressure Metamorphism: Caused by high pressure.
Isostasy
Isostasy refers to the equilibrium between the lithosphere and the plastic mantle.
- Initial situation.
- Formation of a mountain range.
- Subsidence due to loading.
- Melting of ice.
- Isostatic rebound.
Subsidence: When very thick deposits of sediment accumulate in a sedimentary basin, the bottom tends to sink isostatically.
Isostatic Response to Erosion
- Formation of a root under a recently formed mountain range.
- Beginning of erosion.
- Lithospheric unloading due to erosion.
- Isostatic uplift in response to weight reduction.
Relief Factors
- Climate: Controls the acting agents and vegetation cover.
- Lithology: Different rock types are modeled differently; the outcome will depend on their arrangement.
- Human Activity: An increasingly influential factor (urbanization, communication channels), geological causes evolve differently in different stages of maturity.
Morphoclimatic Systems
- Glacial: The glacial climate system favors the accumulation of snow year after year, preventing the development of vegetation.
- Periglacial: The periglacial climate system allows the development of very scarce vegetation; modeling in periglacial mountain areas results in the accumulation of rock fragments.
Features of Mountain Ranges
- Elongated shapes.
- Deformed rocks showing evidence of compressive forces and magmatism.
- Thickened crust, up to 70 km thick.
- Marine fossils are commonly found in the rocks.
Geological Hazards
Seismic Risk: Earthquake disasters are linked to internal geological activity, causing many casualties and significant damage. Not all areas show the same degree of seismic hazard.
Volcanic Risk: The danger of volcanic eruptions depends on the magma’s viscosity and the amount of dissolved gases.
Climate-Specific Landforms
- Desert: Intense rainfall and evaporation mean that liquid water exists only in the soil for a short part of the year.
- Semi-desert: Rainfall is usually irregular and torrential. Vegetation is reduced to shrubs adapted to intense drought.
- Fluvial Modeling: Milder temperatures allow liquid water to be maintained in most landforms throughout the year.
Azonal Landforms
Azonal landforms are not climate-dependent and are not limited to a specific geographical area.
- Coastal Modeling: The coast is where the surf acts, producing a huge variety of landforms.
- Karst Lithologic Modeling: Forms a characteristic relief in areas with soluble rocks.
- Granitic: Chaos of boulders are typical of granitic modeling.