Abstract
ABSTRACTFractured systems developing at the base of temperate glaciers play a significant role in the transport of subglacial water. Their influence on dynamics and hydraulics of glaciers and the seasonal alterations they experience during the hydrological year, remain however, poorly understood, as they lay beyond the reach of most conventional glaciological techniques. In this work, we investigate the seasonal evolution of glacier seismicity in the ablation zone of Rhonegletscher (Switzerland) and focus on basal fracture processes. To do this, we use seismic measurements performed between June 2012 and July 2013 and complementary measurements of surface motion and changes in melt water input inferred from degree day modeling. Results of a spectrogram analysis highlight predominant seismic emissions until end of October 2012 and from mid April 2013 in line with measured surface velocities, and indicate a rapid adaptation of the basal drainage system at initiation and end of the winter period. The analysis of icequakes emitted from two active regions shows that the basal events, due to opening and closing of cracks within fracture networks, persist after winter initiation, and points out the year-long preservation of the associated sources. In this regard, we deduce that basal crack networks aseismically evolve during the winter period.
Highlights
Subglacial water can have a profound impact on glacier and ice sheet dynamics
Beneath ablation zones of temperate glaciers, subglacial drainage systems are usually characterized by a seasonal cycle
Our work addresses two main points: first we give a year-long overview of the continuous glacier seismicity, i.e of all kinds of seismic signals recorded in the study area, and discuss the observed seasonal patterns; second we constrain the role of basal fracture processes in the dynamics and hydraulics of the glacier by focusing on near-bedrock icequakes indicative of opening and closing of basal fractures
Summary
Subglacial water can have a profound impact on glacier and ice sheet dynamics. Depending on the capacity of the subglacial drainage system, incoming water masses may overwhelm or underwhelm the subglacial drainage system and lead to an increase or decrease in subglacial water pressure. Dalban Canassy and others: Seasonal variations of glacier seismicity at the tongue of Rhonegletscher (Switzerland) contrasts with channelized drainage systems, whose morphology is most dynamic during times of elevated water flux. Answering these questions will provide new insights into the formation and evolution of subglacial drainage pathways. The answers require a means to observe basal fracture processes, which are beyond the reach of most conventional glaciological techniques In this concern passive seismic investigations represent an innovative technique for continuous monitoring of nearsurface, intermediate and subglacial environment. To our knowledge we produce the first year-long glacier seismicity record on the ablation zone of an alpine glacier
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