Abstract
This chapter deals with the occurrence, morphology and activity of periglacial landforms in the Hrubý Jeseník Mts. Redistribution of snow during the Last Glacial period, cold climate and the presence of extensive planation surfaces at high elevations have created favourable conditions for the formation and evolution of periglacial landforms, some of which are preserved to this day.
Most of these landforms are relict (tors, frost-riven cliffs, cryoplanation terraces, blockfields, sorted polygons and nets, and large solifluction steps), and only a small part of climatically less demanding periglacial landforms are active (ploughing blocks, earth hummocks, small sorted circles, nivation hollows and small solifluction lobes). Special attention is paid to patterned ground, which provides information about current and past freeze-thaw effectiveness.
Earth hummocks, found at wind-swept sites, on frost-susceptible, fine-grained regoliths, are the most interesting type of patterned ground. Evidence of present-day activity of earth hummocks are distorted soil horizons, vertical and horizontal displacement of clasts, cryoexpulsion features and cracks on crests of earth hummocks, frequent freeze-thaw cycles, and long-term freezing.
The origin of earth hummocks has been identified as being at the break of the Subboreal/Subatlantic. The occurrence and activity of earth hummocks, sorted circles and ploughing blocks at several sites above the alpine timberline of the Hrubý Jeseník Mts. allows us to regard these areas as parts of the mountain periglacial zone.