Polar and alpine environments - Fundamentals of the Physical Environment - page 599

(a)

Secondary
inflow

Anabatic flow

1000 hrs

(b)

Plate 24.3 Sun cups formed on the sunlit surface of snow-
pack micro-relief. Their shape and orientation will change as
the sun moves around during the day.
Photo: Ken Addison

Gravity outflow

Katabatic flow

Slope variability also generates random changes in
parameters such as shade, wind exposure, air and water
drainage. We move imperceptibly into the microclimate
zone, with its most subtle interactions between atmos-
phere and surface. Energy and moisture transfers are
influenced at successively smaller scales by the presence
or absence of vegetation, the juxtaposition of snow, soil
and vegetation surfaces, the albedo of snow, and the
specific heat capacity and thermal conductivity of soils.
An example of the extremely small spatial and temporal
scales of microclimate occurs where the influence of
albedo and diurnal shifts in radiation and air temperature
on melt potential at a glacier surface is evident in the
evolution of sun cups of more than 10 cm vertical
amplitude ( Plate 24.3 ).

1700 hrs

(c)

0800 hrs 1100 hrs 1400 hrs

Figure 24.6 The development of (a) anabatic and (b)
katabatic mountain winds and (c) the associated development
of rising mountain cumuliform cloud. See also Figure 8.14.
Source: Adapted, in part, from Barry (1992)

the mountains. Its key components are slope angle and
aspect, which allow us to calculate the short-wave
radiation flux for any particular latitude and time. Their
impact is illustrated by the receipt of 1·2, 2·3 and 4·3 times
the incident radiation on south-facing ( adret ) compared
with north-facing ( ubac ) slopes at 5

ALPINE MOUNTAIN
ENVIRONMENTS

latitude.
Differences between east-west facing slopes are more
subtle and their impact depends on other conditions
and processes (see Figure 8.11 ). Thus afternoon direct
sunlight may melt more snow than a similar morning
flux because ambient heat during the day has already
raised its temperature. Insolation asymmetry accentuates
other differences. Anabatic flow, for example, may be
accompanied and enhanced by progressive morning
development of mountain cumulus on sunlit slopes
( Figure 24.6c ).

,25 and 45

Physical geology of Earth's principal
mountain systems

Mountain environments carved primarily from the three
most recent, Phanerozoic orogenic episodes of Earth
history form high-energy, high-stress and high-sensitivity
landsystems. Their formation and relocation by plate
collisions cross conventional geographic patterns and
morphogenetic regions based on climate zones (see Figure
13.3 ). Mountains extend almost continuously for 29,000