Polar and alpine environments - Fundamentals of the Physical Environment - page 609

Tibetan Plateau Greater Himalaya Lesser Himalaya Sub Himalaya Figure 24.12

Block section through the
Himalayas, from north (left)
to south (right).
Source: Modified from Vuichard,
Institute of Mineralogy,
University of Berne

8000 m

5000 m

4000 m

2500 m

300 m

150 km

Quaternary sediment
Tertiary molasse
Tertiary granite
Ophiolite

Upper Palaeozoic - Mesozoic sediments
Lower Palaeozoic sediments
Archaean - Proterozoic basement

restricted parts of the mountain systems. This is enhanced
by close interaction with mountain climates and eco-
systems and by partial geomorphic isolation by the
timberline and glacially excavated lake basins. The latter
both act as major buffers to onward sediment transfer
to the predominantly fluvial systems below. However, the
landsystem is not isolated from endogenetic influences.
Altitude, high gravitational potential and recent or on-
going tectonic activity combine to make it one of Earth's
most geomorphically active environments, in which
catastrophic events may disguise continuous but less
dramatic denudation.

Chapter 15. Glaciers promote active denudation, with
meltwater and sediment transfers only bypassing the
alpine slope system in the dwindling number of glaciers
terminating below regional timberlines. Their presence
'insulates' subglacial surfaces from other alpine processes
but actively promotes them at their perimeter (especially
in supraglacial rock walls) by influencing radiation,
moisture and wind aspects of the topoclimate.
The cryonival belt is found in all alpine mountains,
irrespective of whether they have a permanent snowline
and/or glaciers. Geomorphic processes are driven by
short-term (diurnal/seasonal) mass and energy budgets of
the snowpack and ground ice. Nivation concentrates frost,
cold-chemical weathering and associated debris transport
under and around permanent and semi-permanent snow
beds. These processes are especially active around their
lower margins, in meltwater percolation and wet snow
zones and during the ablation season. On low to moderate
angle slopes they may erode shallow basins which feed
debris fans or terraces through melt chutes or by solifluc-
tion. Debris shed by frost weathering, from rock walls
overlooking snow beds, slides over their surface to form
a protalus rampart at their foot ( Plate 24.10 ). Snowpack
itself may move as slush avalanches during late-season
melting, and more general avalanching from snowfields

Cryonival (snow and ice) belt
The alpine zone is a glacial-cryonival-slope landsystem
experiencing high energy and sediment transfers ( Figure
24.14 ). It is best developed in areas of intense Pleistocene
alpine glaciation which excavated deep glacial troughs,
tributary cirques and oversteepened rockwalls. Consider-
able volumes of debris were plastered indiscriminately or
as retreat moraines on lower slopes during deglaciation.
Rockwall and moraine-covered slopes are fully integrated
into the alpine landsystem, which reworks this glacial
'inheritance' ( Plate 24.9 ). The continuing role of modern
alpine glaciers and mountain ice caps is covered in