Geology Reference
In-Depth Information
must note that this phenomenon fi ts well with our current understanding of permafrost
and ground ice conditions in arctic regions today.
Slightly more ambiguous phenomena are the angular rock-rubble accumulations,
known variously as “blockfi elds,” “boulder fi elds,” or “felsenmeer,” that cover many of
the uplands and low mountain ranges of the mid-latitudes (Derbyshire, 1973; Dylik, 1956;
Clark et al., 1992; Kwon, 1978, 1979; Lewis, 1988; Pissart, 1953; Smith, 1962). They are
usually developed upon hard, siliceous rocks such as sandstone, quartzite, and granite
(Figure 13.3A). These are the “periglacial facies” of Lozinski (see Chapter 1). Their
origin is not fully understood and the broader issue of cryogenic weathering must be
considered in their interpretation (see Chapter 4). While frost-wedging along joints
and bedding planes is applicable to sandstone bedrock, differential thermal expansion of
silica minerals under cryogenic conditions may be more appropriate to explain rock
(A)
(B)
Figure 13.3.
Relict bedrock features of supposed frost-action signifi cance. (A) Blockfi eld devel-
oped on granite, Mount Wielki Szyszak, Karkonosze, Car pathian Mountains, southern Poland. Note
that the “periglacial facies” that Lozinzki described were in sandstone and further to the east in
the Gorgany Range. Photograph is supplied courtesy of R. Zurawek. (B) Angular hillslope tor, 10 m
high, fashioned by Pleistocene frost action and formed in metadolomite, Dartmoor, North Devon,
UK. Photograph is supplied courtesy of Professor D. Mottershead.
