because accumulation exceeds ablation (melting) in a location. This
accumulation zone after it thickens to more than 30 m begins to
For a glacier to survive it must have a consistent and
persistent accumulation zone.
To diagnose a glacier
that is disappearing look for
1) Emergence of rock
outcrops in accumulation zone (upper region) of the glacier.
2) Recession of the
upper margins of the glacier around the accumulation zone.
3) Lack of consistent
snowcover at the end of the summer in the accumulation zone of
Published Paper in The Cyrosphere 2010
Quaternary International Paper 2011
Why these criteria?
Glaciers respond to climate in an attempt to achieve
equilibrium. A glacier advances due to a climate
cooling/snowfall increase that causes positive mass balance.
A climate warming/snowfall decrease leads to negative mass
balances and glacier retreat. To reestablish equilibrium a
retreating glacier must lose enough of its highest ablating
sections, usually at the lowest elevations, so that accumulating
snows in the near the head of the glacier once again are
equivalent to overall ablation, and an equilibrium balance is
approached. If a glacier cannot retreat to a point where
equilibrium is established, it is in disequilibrium with the
climate system. A glacier that is in disequilibrium with present
climate will melt away with a continuation of this climate.
We often focus on
terminus change of a glacier which tells us how the glacier is
currently responding to recent climate. A glacier can retreat
rapidly and still survive if it has an accumulation zone.
Thus, to forecast survival we need to focus on the accumulation
zone, not just the terminus. If the accumulation zone no
longer retains accumulation consistently it will begin to thin.
A glacier needs 50-70% of its surface area to be snowcovered
event at the end of the summer to be healthy. A thinning accumulation zone is evident when the margins of
the glacier in this accumulation zone-upper potion of the glacier recede.
Also new outcrops of rock maybe exposed in the accumulation
zone due to thinning. This has been
observed both in the North Cascades and on Swiss glaciers.
Below are examples
of glaciers that have disappeared, will disappear and that can
retreat to a new position of equilibrium with current climate.
This is not to say that further warming will not eliminate many of
the the glaciers that have an accumulation zone today. Sometimes adjacent glaciers can have
differing forecasts based on their varied response to recent
climate. It is unusual for an entire mountain range to be
inhospitable to glaciers today.
of the rapid loss of all glaciers in Glacier National Park or the
Nepal Himalaya are exaggerated. In each case the glaciers
are retreating notably, but some of the glaciers still have
persistent accumulation zones. In the Himalaya the most
photographed glacier is probably the
Glacier on the south
side of Mount Everest. Above the famed Khumbu Icefall
there is a persistent accumulation zone, indicating it can
retreat to a new point of equilibrium with current climate.
Above is Foss Glacier in 1985, still
covering a large area of the east slope of Mount Hinman.