Solifluction (frost-creep and gelifluction) is an
important periglacial process and forms sheets,
lobes, terraces, and ploughing boulders. Such
landforms are more common in Low Arctic,
subarctic and alpine environments than in High
Arctic polar deserts, which are too dry to promote
much solifluction. Tongue-like lobes are common
in the tundra and forest tundra, where some
vegetation patches occur (Plate 11.8). Solifluction
lobes tend to form below snow patches. Typically,
they are tongued-shaped features, 10 to 100 m
long, 5 to 50 m wide, with steep frontal margins
or risers, which may stand 1.5 m high. Frostsorting
processes often bring about a concentra -
tion of clasts around a lobe’s outer margins, which
are called stone-banked lobes; lobes lacking
marginal clasts are turf-banked lobes. Areas of
widespread solifluction lobes are solifluction
sheets, which can produce smooth terrain with
low slope gradients (1° to 3°) where vegetation is
scanty. Terraces are common on lower slopes of
valleys (Plate 11.9). Steps are terrace-like land -
forms that occur on relatively steep slopes. They
develop from circles, polygons, and nets, and run
either parallel to hillside contours or become
elongated downslope to create lobate forms. In
unsorted steps, the rise of the step is well vegetated
and the tread is bare. In sorted steps, the step is
edged with larger stones. The lobate varieties are
called stone garlands. No step forms are limited
to permafrost environments. Ploughing boulders
or ploughing blocks move down slopes through
the surrounding soil, leaving a vegetated furrow
in their wake and building a lobe in their van
(Plate 11.10).