Environmental Engineering Reference
In-Depth Information
Figure 15.1 Global distribution of modern and Late
Pleistocene ice sheets and glaciers in (a) the northern and (b)
the southern hemispheres. The maximum ice surface elevation
of each major ice sheet is shown.
GLACIER ICE
Glacier ice is fashioned from snow, hail, sublimation (direct deposition) and rain or dew
which subsequently freezes. Snow is transformed through several recognized stages
before becoming mature glacier ice capable of substantial geomorphic activity. Snowpack
is highly porous and held together by a frozen crystal lattice; pores contain air and,
depending on temperature, perhaps water vapour and/or water. In essence, transformation
progressively expels air and reduces void space through autocompaction . This process is
assisted by the lowering of freezing point under higher pressure. Further snowfall
increases overburden pressure on the snowpack, which reaches its pressure - melting
point at delicate snowflake tips. Supercooled meltwater diffuses to areas of lower
pressure in the pack before regelation or refreezing/recrystallization occurs. This process
has some affinity with rock crystallization and metamorphism. In addition, localized melt
through insolation, advection or geothermal heating assists consolidation if water then
regelates in colder parts of the pack. Tiny geometrically complex snowflakes are
transformed into assemblages of progressively larger, amorphous ice crystals. Gravity
tends to draw this downhill as regelation creep , which initiates ice flow. All three
processes exert a major influence on subsequent glacier behaviour. Density, measured in
g cm −3 , increases rapidly
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