Glaciohydraulic seismic tremors on an Alpine glacier

Abstract

Abstract. Hydraulic processes impact viscous and brittle ice deformation. Water-driven fracturing as well as turbulent water flow within and beneath glaciers radiate seismic waves which provide insights into otherwise hard-to-access englacial and subglacial environments. In this study, we analyze glaciohydraulic tremors recorded by four seismic arrays installed in different parts of Glacier de la Plaine Morte, Switzerland. Data were recorded during the 2016 melt season including the sudden subglacial drainage of an ice-marginal lake. Together with our seismic data, discharge, lake level, and ice flow measurements provide constraints on glacier hydraulics. We find that the tremors are generated by subglacial water flow, in moulins, and by icequake bursts. The dominating process can vary on sub-kilometer and sub-daily scales. Consistent with field observations, continuous source tracking via matched-field processing suggests a gradual up-glacier progression of an efficient drainage system as the melt season progresses. The ice-marginal lake likely connects to this drainage system via hydrofracturing, which is indicated by sustained icequake signals emitted from the proximity of the lake basin and starting roughly 24 h prior to the lake drainage. To estimate the hydraulics associated with the drainage, we use tremor–discharge scaling relationships. Our analysis suggests a pressurization of the subglacial environment at the drainage onset, followed by an increase in the hydraulic radii of the conduits and a subsequent decrease in the subglacial water pressure as the capacity of the drainage system increases. The pressurization is in phase with the drop in the lake level, and its retrieved maximum coincides with ice uplift measured via GPS. Our results highlight the use of cryo-seismology for monitoring glacier hydraulics.

Breaking the Ice: Identifying Hydraulically Forced Crevassing

“…This glacier is an ideal environment for studying potential hydraulically forced crevassing due to the high levels of surface melt present. Previous studies have used icequakes to infer hydraulically forced crevassing using auxiliary information, such as glacier speed up (Helmstetter et al, 2015), or the presence of meltwater (Carmichael et al, 2012(Carmichael et al, , 2015Lindner et al, 2020). Others have used seismicity to show that crevassing exhibits tensile faulting (Mikesell et al, 2012;Neave & Savage, 1970;Roux et al, 2010;Walter et al, 2009) and anisotropy (Lindner et al, 2019).…”

On the Green's function emergence from interferometry of seismic wave fields generated in high-melt glaciers: implications for passive imaging and monitoring

“…Gravity-driven transport of meltwater creates transient forces on the bulk of the Earth (e.g. Schmandt et al, 2013;Gimbert et al, 2014) and surrounding ice (Gimbert et al, 2016) that generate a mix of body and surface waves (Lindner et al, 2020;Vore et al, 2019). Meltwater flow noise is recorded continuously at frequencies of 1-20 Hz as shown in the 1-month spectrogram of ground velocity at Glacier d'Argentière (Fig.…”

“…Such topics are currently investigated with active seismic experiments or through the spatiotemporal evolution of passive seismicity and associated source mechanisms (e.g. Walter et al, 2008;Bartholomaus et al, 2015;Preiswerk et al, 2016;Podolskiy et al, 2017;Lipovsky et al, 2019). Passive seismic monitoring of glaciers could lead to the detection and understanding of processes related to climate conditions, glacier hydraulics, and ice flow dynamics, which today are labor-intensive to investigate with active geophysical measurements.…”

“…Walter et al, 2009;Mikesell et al, 2012), basal processes (e.g. Winberry et al, 2013;Röösli et al, 2016a;Lipovsky et al, 2019), glacier hydrology (Bartholomaus et al, 2015;Gimbert et al, 2016), and iceberg calving (e.g. Walter et al, 2010;Bartholomaus et al, 2012;Sergeant et al, 2016Sergeant et al, , 2018.…”

“…Condition (i) can compensate for lack of condition (ii). However, microseismicity generated on glaciers is often confined to narrow regions such as crevasse margin zones (Roux et al, 2008;Mikesell et al, 2012) or other water-filled englacial conduits (Röösli et al, 2014;Walter et al, 2015;Lindner et al, 2020). This often prevents the occurrence of homogeneous source distributions on glaciers.…”