J. Warburton et Cr. Fenn, UNUSUAL FLOOD EVENTS FROM AN ALPINE GLACIER - OBSERVATIONS AND DEDUCTIONS ON GENERATING MECHANISMS, Journal of Glaciology, 40(134), 1994, pp. 176-186
Observations are presented on a particularly unusual sequence of flood
events witnessed at Bas Glacier d'Arolla, Switzerland, in July 1987.
The sequence was triggered by heavy rain storms, and involved a suprag
lacial ''overflow event'' (water cascading from moulins over the snout
of the glacier) succeeded, following a series of ''mini-floods'', by
a subglacial ''outburst event''. Available hydrological and geomorphol
ogical data are used to assess the significance of the floods and to d
educe likely explanations for each phase of the flood-event sequence.
Bottom-up surcharging of a poorly developed subglacial drainage system
is the preferred explanation for the overflow event. The subglacial o
utburst is explained as an extreme ''spring event''. Hydraulic jacking
is implicated, but not proven, during both events. Whilst the flood s
equence was triggered by an intense storm, englacially stored waters a
re believed to have contributed most of the flood waters.