Geography · Ch 11 — Geomorphic Processes
Endogenic Processes
Endogenic Processes
The earth’s internal heat is the engine that drives endogenic geomorphic processes. This energy comes from several sources: radioactivity, rotational and tidal friction, and the primordial heat left over from the earth’s origin. Because this heat flows outward through the lithosphere, it creates geothermal gradients and heat flow from within, which in turn set off two broad kinds of activity — diastrophism and volcanism.
The action of these forces is not uniform across the planet. Geothermal gradients, heat flow, crustal thickness, and crustal strength all vary from place to place. As a result, the tectonically controlled original crustal surface is uneven — the forces that build the crust do not act equally everywhere.
Diastrophism
Diastrophism covers all processes that move, elevate, or build up portions of the earth’s crust. It includes four distinct kinds of activity:
- Orogenic processes — mountain building through severe folding, affecting long and narrow belts of the earth’s crust.
- Epeirogenic processes — uplift or warping of large parts of the earth’s crust.
- Earthquakes — local, relatively minor movements.
- Plate tectonics — horizontal movements of crustal plates.
In orogeny, the crust is severely deformed into folds. In epeirogeny, the deformation is simpler. The key distinction: orogeny is a mountain-building process, while epeirogeny is a continental-building process.
| Feature | Orogeny | Epeirogeny |
|---|---|---|
| What it builds | Mountains | Continents |
| Nature of deformation | Severe folding | Simple deformation (uplift or warping) |
| Area affected | Long, narrow belts | Large parts of the crust |
Through orogeny, epeirogeny, earthquakes, and plate tectonics, the crust can undergo faulting and fracturing. All these processes cause pressure, volume, and temperature (PVT) changes in rocks, which in turn induce metamorphism.