Geoscience Reference
In-Depth Information
F
IG.9
Above
, A wind-scoured, boulder-covered summit plateau in the 'arctic' soil zone; Cairngorm Mountains,
Scotland. (Photograph D. F. B.).
Below
, Soil zones defined by climatic trend lines on a transect across Scotland. (Adapted from J.S. Bibby
1986.)
Temperatures fall with increasing altitude. Although this drop (the 'lapse-rate')
varies seasonally at one place, and from place to place, it averages close to 0.6°C for
each 100 metres rise in altitude. For example again, in the Pennines the summit area
of Kinder Scout, at 630 metres, has an average temperature some 3°C lower than at
Stockport, only 18 kilometres to the west but at an altitude of 100 metres.
The climatic influences on the soils of the highland zone are accentuated by the
prevalence of hard, less easily weathered rock types in the west and north. Within the
highland zone, there are distinct vertical zones that result from the regional relation-
ships between altitude, rainfall and temperature. Figure 9 illustrates this by a schem-
atic cross section through Scotland showing three soil zones, divided by approximate
climatic boundaries that fall steadily in altitude from east to west. An upper 'arctic'
zone starts above about 400 metres in the west, but not until above some 700 metres
in the central Grampians. (It would be much higher than the actual land surface in
the east). Within this zone, bare rock surfaces are frequent together with areas of im-
mature shallow soils, often mobile and frost-heaved. These are seen on the summits
of the Cairngorms at around 900 metres (
Fig. 9
) where soil conditions have much in
