In June 1818, ice falling from the tongue of the Giétro glacier had in effect blocked the valley of Mauvoisin in Switzerland. Water was building up behind this ice dam to dangerous levels, and engineers were called in to release it gradually. They drilled a hole through the ice, but it did not relieve the water pressure quickly enough. On 16 June at 4.30pm the ice dam burst, disintegrating and releasing all the water at once.
The result was a catastrophic “glacial lake outburst flood”, a phenomenon characterised by extremely high rates of water flow. Warnings did not travel as fast as the sudden rush of 20m cubic metres (4.4bn gallons) of water, which swept away bridges and buildings in its path, killing 44 people and many animals.
The event produced a new awareness of this hazard, and today the valley waters are safely contained by the giant Mauvoisin dam. The flood also triggered a new scientific interest in glaciers. Scientists visiting the site found boulders left by previous glacial activity, suggesting that, contrary to their belief, glaciers were not static, but advanced and retreated over time. A conference in Switzerland this week commemorates the tragedy, and its role in shaping glacial theory.