Seismic and Geodetic Observations of Accelerated Sliding at Haupapa/Tasman Glacier, New Zealand

Rain-induced accelerations of Haupapa/Tasman Glacier are accompanied by abundant seismicity. This seismicity reveals some of the glacial processes occurring at times of accelerated glacier sliding and those related directly to surficial water inputs.To study the processes occurring during rain-induced accelerations a network of seismic and geodetic sensors was deployed on the lower Haupapa/Tasman Glacier for four months in 2016. Seven categories of seismicity were defined during the study period. Glacier source processes were inferred for these categories based on their waveform characteristics, and each source was then compared to meteoric and geodetic data to discern spatial and temporal relationships. Of the seven categories of seismicity only the seismic events associated with crevasse opening were found to correlate with rain rate. Increased crevassing rate likely results from two factors: 1) increased extensional strain rates following the propagation of a subglacial cavitation front during transient accelerations and 2) hydrofracture due to the accumulation of rain in crevasses. Strain-driven crevassing is associated only with glacier acceleration, but crevasse opening via hydrofracture is inferred to occur independently of strain changes such that it is an active process at any point following heavy rainfall. Basal seismicity was not observed to respond to changes in glacier velocity or inferred subglacial water pressure, although this may be due to limitations in the seismic event detection technique.