Avalanches -- triggered from the valley

Everybody knows that skiers swishing down steep slopes can cause extensive slab avalanches. But there is a less well known phenomenon: A person skiing a gentle slope in the valley triggers a slab avalanche on a steeper slope, sometimes several hundred meters further uphill. This scenario doesn't seem to make sense – yet it claims human lives year after year.

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<p><a href="http://www.physorg.com/news147449264.html">Avalanches -- triggered from the valley</a></p> <p>Everybody knows that skiers swishing down steep slopes can cause extensive slab avalanches. But there is a less well known phenomenon: A person skiing a gentle slope in the valley triggers a slab avalanche on a steeper slope, sometimes several hundred meters further uphill. This scenario doesn't seem to make sense – yet it claims human lives year after year.</p>