Summer 2007 - The Alpine Club of Canada

Glaciers shaped by weather, gravity and setting
BY PABLO WAINSTEIN
As climbers, skiers and lovers of
the outdoors we are constantly
amazed by the mountain
landscape that forms our playground. Our
photo archives are stuff ed with pictures
of glaciers and the landscapes that have
been shaped by ice throughout thousands
of years. Rock walls, open wide valleys,
moraines and glaciers are all linked by
a common geological history of ever
changing features driven by slow but
incredibly big forces.
Glaciers are active systems that
live in a subtle equilibrium with the
surrounding environment. Th ey grow and
shrink; advance and retreat, all delicately
governed by a mass balance between what
they receive as snow intake, what they
expel as meltwater, and by sublimation
(the conversion between the solid and the
gas phases with no intermediate liquid
stage).
Th e main mass inputs are achieved
through precipitation as snow and rain
that can refreeze in the glacier’s interior,
and from avalanching from affl uent
valleys. Th e main output by far is melting
and is presented as meltwater. Secondary
processes such as calving and ice
avalanching also play major roles. Calving
is the process by which ice slabs are down
wasted into the water if the glacier ends
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28 Alpine Club of Canada ● Gazette ● SUMMER 2007
in a lake or the sea. On the contrary, if the
glacier ends in dry land – as the majority
of alpine glaciers do – the process is
called ice avalanching. Th e latter is
slightly less frequent since there is no
water to exert buoyancy pressures under
the ice and fracture it. Unfortunately,
terminology is sometimes confusing but
its goal is to be as descriptive as possible.
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Even though we see many iced areas
in the mountains, not all can be called
glaciers. Glaciers are made out of ice that
experience movement and deformation.
As such, they require a minimum size and
depth that will promote movement due
to the action of gravity.
Glaciers have two recognizable areas
that are fundamental for their survival: an
accumulation zone and an ablation zone.
Th e two are separated by what is called
the ‘equilibrium line’. Th e accumulation
area is where snow falls and fortunately
is preserved throughout the year, adding
mass to the glacier. Th e ablation area is
where there is more melting than mass
infl ow. Both need to be in equilibrium
in order for the glacier to maintain a
constant size. Nowadays many glaciers
present a considerable meltdown due
to warmer/drier winters that suppresses
precipitation, and/or warmer summers
that incite a larger meltdown. Th ere are
some exceptions, such as Taku Glacier
in the Juneau Icefi eld in Alaska, which is
still growing mainly as a result of its huge
accumulation area and its large inertia,
but these are just that – exceptions to the
rule.
Alpine Club of Canada member Pablo
Wainstein is a hydraulic civil engineer
and PhD student with the University of
Calgary’s Department of Geography.