Page 305 - Fundamentals of Geomorphology

288 PROCESS AND FORM

Plate 11.4 Earth hummocks, Drakensberg, Lesotho.
(Photograph by Stefan Grab)

surface materials. Earth hummocks occur mainly in Stripes
polar and subpolar regions, but examples are known
from alpine environments. They are present and peri- Stripes, which are not confined to periglacial environ-
odically active in the alpine Mohlesi Valley of Lesotho, ments, tend to develop on steeper slopes than steps.
southern Africa (Grab 1994, 2005) (Plate 11.4). Sorted stripes are composed of alternating stripes
of coarse and fine material downslope (Plate 11.3b).
Sorted stripes at High Pike in the northern English
Steps
Lake District occur at 658 m on a scree with an aspect
◦
Steps are terrace-like landforms that occur on fairly of 275 and a slope angle of 17–18 (Warburton
◦
steep slopes. They develop from circles, polygons, and and Caine 1999). These stripes are formed at a
nets, and run either parallel to hillside contours or relatively low altitude, possibly because the scree
become elongated downslope to create lobate forms. has a large proportion of fine material suscepti-
In unsorted steps, the rise of the step is well vege- ble to frost action and is free of vegetation. The
tated and the tread is bare. In sorted steps, the step sorted stripes are still active. Non-sorted stripes
is edged with larger stones. The lobate varieties are are marked by lines of vegetation lying in slight
called stone garlands. No step forms are limited to troughs with bare soil on the intervening slight ridges
permafrost environments. (Plate 11.5).