Abstract
A major ice collapse (20.000 m3) from a hanging glacier on Mount Eiger,
Switzerland was recorded by a small aperture array as a broadband
(0.1-10 Hz) infrasound signal. Array analysis reveals that the high
(~ 3 Hz) frequency signal is infrasound produced by the
moving ice mass, and its back-azimuth variation with time tracks the ice
mass trajectory and provides a mean velocity estimate. Infrasound
frequency is used to estimate a radius, that is in good agreement with
the volume estimate from field observations. The low
(~0.1 Hz) frequency oscillation is modeled in terms of
the velocity field (wind), which the moving ice mass induces on the
surrounding air, producing pressure variations at the different
elements. These results show how infrasound array observations may
provide quantitative information of glacier collapse and ice avalanche
volume. This opens new perspectives for monitoring avalanching glaciers
and providing warning for break-off events.