Landforms at the angle of repose

Colluvium is material moved by gravity. Mass wasting is a generic term for all manner of gravity-driven processes and deposits. Colluvial or talus fans have much in common with alluvial fans, and may grade imperceptibly into them. Colluvium rests at the angle of repose; it’s steeper than alluvial fans and material is more angular than water-transported rock.

Here are two kinds of habitats on colluvial slopes, keyed to frequency of disturbance.

Size of colluvial deposits depends upon the jointing pattern of source rock in cliffs above, intensity of freeze-thaw action, and, of course, time. Southeast colluvium has been accumulating for about 12,000 years, an eyeblink compared to the life span of talus cones in unglaciated mountains of the desert southwest, for example.

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