CRYOPLANATION - A UNIQUE QUATERNARY PHENOMENON?

One of the tenets still present in the geomorphology of Quaternary period is that smooth preglacial slopes have become transformed into stepped slopes through a set of surface processes embraced by the term ‘cryoplanation’. Although this transformation is poorly constrained quantitatively in respect to rates of rock-cut cliff retreat and terrace enlargement, high efficacy of cryoplanation has been often assumed.

However, field evidence accumulates to suggest that benched profiles evolve slowly, are much controlled by geological structure, and may have a substantial pre-Quaternary inherited component. Observations reported here come from the present-day maritime periglacial environment of Svalbard and the Pleistocene periglacial zone of Central Europe. In southwest Svalbard, late Pleistocene and early Holocene raised marine cliffs have undergone insignificant retreat over 10⁴ yr time scale, as negligible volumes of weathered material at cliff base and exposed marine pebbles below the cliffs indicate. In the Sudetes mountains, Central Europe, benched profiles are present in areas outside the limit of Pleistocene continental glaciations or above the trimlines within this limit. Given pre-Eemian age of the last glaciation in the area it is suggested, that one cold period of c. 100 kyr duration is not long enough to allow for creation, or re-creation of benched slopes. Furthermore, certain rock types appear not to support benched profiles, even if exposed to periglacial conditions throughout the Quaternary. Coarse granite in particular is hardly prone to postulated cryoplanation, whereas moderately steep slopes in foliated metamorphic rocks show stepped profiles relatively often. Many cliffs are developed along linear outcrops of resistant rocks and probably increase in height rather than retreat.

The paradigm of powerful cryoplanation and significant remodelling of periglacial upland surfaces in the Quaternary is increasingly questioned. Limiting the role of cryoplanation implies that periglacial uplands may act as environmental archives of the Quaternary in much higher degree than previously thought.