Environmental Engineering Reference
In-Depth Information
mature debris slope is usually concave, reducing from 35°-43° at the rock-wall foot to
25°-35° in mid-slope (the approximate internal friction angle of granular debris) and 0°-
5° at the foot. This reflects reworking according to grain/block size, shape and degree of
disturbance.
Plate 25.9
Talus cones, talus sheets and a paraglacial
landslide (left) below frost-weathered rock pinnacles in Nant
Ffrancon, North Wales. Although they are largely inactive,
relic forms, their surfaces are scarred by recent and
contemporary debris flow tracks lines by levées.
Photo: Ken Addison.
ALPINE SOILS
Pedological development reflects the inherent instability and sensitivity of alpine
environments, with frequent occurrence of buried soils among the spatial mosaic of other
geoecological processes. The shallow nature and short-term (seasonal) disturbance of
regolith discourages the development of anything more than raw, lithomorphic soils
under a humic layer on crests and the steeper parts of talus slopes, corresponding to
Leptosols (FAO classification). They are A-R soils with a medium to coarse texture, with
gelic leptosols
on better drained slopes and
gelic gleyed leptosols
where drainage is poor.
Cambisols
are found on gentler and more stable slopes, with a strongly humic Ao horizon
due to slower decomposition rates at lower temperatures. Acid ericaceous and coniferous
litter creates a mor humus. Cambisols show at least a weak development of continuous
B-C horizons and appear most commonly as
gelic dystric cambisols
; they include
alpine
