In geomorphology, altiplanation or cryoplanation refers to the process of relief reduction or gradual planation (i.e., the smoothing of the surface) under periglacial conditions.
Two mechanisms are involved under altiplanation:
- The destruction of upstanding relief features by frost wedging or nivation, and
- The accumulation of debris in depressions or as terraces.
The gradual accumulation of debris leads to altiplanation terraces. In many areas where only partial altiplanation has been achieved, their altiplanation terraces are noticeable such as those of Cox Tor on
Dartmoor, England.
Terraces formed by altiplanation or cryoplanation are called altiplanation terraces. Altiplanation landforms are characterized by terraces as gently inclined or nearly horizontal bedrock-cut benches on slopes, spurs, and on broad interfluves that are formed by the parallel retreat of steeper slope segments under periglacial conditions.
Additionally, with the effect of the altiplanation process on the landscape, the vegetation on these frost-altered terraces is also reshaped. The vegetation tends to be uniquely uniform both laterally and vertically.
This unique periglacial landforms based on the freeze-thaw cycles are customarily found in Arctic periglacial regions of Eastern Siberia and Alaska. They may also be found in areas that currently or have some time in the past experienced intense seasonal freezing or permafrost.