What Happens: Glaciers are in constant motion,
so parts of the ice pack can become unstable because of factors like natural movement
and changes in temperature. Glaciers on steep slopes, in particular, tend to break
off rather than melt away, causing ice avalanches. In April four skiers in the
Mont Blanc range perished when a serac an ice pinnacle formed where the glacier's
surface is torn by cracks-broke away and crushed them. The most catastrophic scenario
is when the front of a glacier breaks off, which can happen when meltwater at
the glacier's base separates the ice from the bedrock.
How to Fix It: Preventing ice chunks from
breaking off is impossible, but it is possible at some sites to predict when and
where an ice avalanche might occur. In Switzerland, scientists are experimenting
with an early-warning system on the Eiger that uses lasers and telemetry to monitor
a serac's advance. When the serac starts to pick up speed, usually a sign it will
fall within days, officials can be warned.
Flash Floods from Glacial Lakes
What Happens: Glacial lakes form when meltwater
fails to drain away through the usual channels and collects instead in basins
created by the glacier itself. Such lakes are normally found in front of the glacier,
with the rock debris pushed ahead by the glacier's advance forming a dike that
holds the water in. More rarely, lakes can form next to or even on top of glaciers.
Danger arises when the meltwater level increases during warm spells, often coupled
with heavy rains. As the water pressure builds, the lake can simply flood its
banks or blast through them, a phenomenon known as outburst. The resulting torrent
hurls rock, mud, ice and just about everything else in its way down the mountainside.
Last year a lake flood on Switzerland's Weingarten glacier near the village of
Täsch damaged several houses.
How to Fix It: Pump out the lake. Once
water levels recede, natural channels can be cut to divert the water. Another
option is to shore up the lake banks with concrete to prevent an outburst.
What Happens: "Water pocket" is the term used
to describe any large accumulation of water under a glacier. The pockets can be
caused by the temporary blockage of a subglacial river system combined with warm
weather. But because the formation of water pockets can't be directly observed,
scientists don't understand them well. These accumulations are especially dangerous
since early detection is impossible. Critical mass is reached when too much water
builds up inside or under the glacier, possibly due to high temperatures and recent
heavy rains. The pressure then becomes too great and chunks of the ice wall can
pop out like corks, releasing a torrent of water and debris down narrow mountain
streams, catching people unaware. In 1994 on the Bodmer glacier in Switzerland,
a water-pocket outburst ripped out a bridge on its way into the valley.
How to Fix It: At present, there is no
way to prevent water pockets from forming. And since they can't be detected either,
the best we can do is hope not to be in the wrong place at the wrong time.