Interrogating a Surging Glacier With Seismic Interferometry

• Published in: Geophysical research letters 2019-07, Vol.46 (14), p.8162-8165
• Main Author: Aster, Richard C.
• Format: Article
• Language: English
• Subjects: Background noise; Bottom friction; Crevasses; Earth; Friction reduction; Glaciation; Glacier flow; Glaciers; Glaciohydrology; Hydrology; Hydrostatic pressure; Ice sheets; Imaging techniques; Interferometry; Internal water; Methods; Monitoring methods; Noise monitoring; P-waves; Seismic activity; Seismic waves; Seismograms; Seismology; Surface waves; Surging (ship motion); Temporal variations; Water flow; Water pressure; Water storage
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL084286

Seismic interferometry can be spectacularly sensitive to temporal changes within the Earth. Zhan (2019, https://doi.org/10.1029/2019GL082411) analyzed 12 years of data from seismic stations situated near Bering Glacier, Alaska, that spanned a 2008–2011 surge. Interferometrically isolated glacier‐crossing surface waves revealed an anisotropic seismic wave speed decrease during the surge. 1‐D and 3‐D modeling suggests pressurized englacial water flow being stored and guided by a network of basal crevasses, thereby sustaining high water pressure at the bed and supporting the high surge velocities. This result is demonstrative of the potential for seismic interferometry and other cryoseismological methods to continuously monitor and reveal changes within dynamic glacial‐hydrological systems. Plain Language Summary Seismology offers increasingly sensitive methods for monitoring and imaging the subsurface by processing of long‐term continuous background “noise” seismograms. Zhan (2019, https://doi.org/10.1029/2019GL082411) applied such an approach to achieve new insight into internal changes accompanying a 2008–2011 surge at Bering Glacier, Alaska, during which the flow speed accelerated by over an order of magnitude (from approximately 0.5 to 9 m/day). Changes near the glacier bed during the surge are detectable as a slowing down of seismic waves, from which the geometry of glacial water storage and drainage can be constrained. The study concludes that crevasses near the base of this glacier store and directed internal water flow, thus reducing glacier‐bed friction and allowing the glacier to dramatically accelerate. This benchmark study, in association along with other pioneering examples, demonstrates great potential for noise‐based seismic monitoring to take the measure of and reveal hidden processes within Earth's rapidly changing glaciers and ice sheets. Key Points A surging glacier has been studied for the first time with seismic interferometry Seismic surface wave speed changes implicate basal crevasses in guiding basal hydrology during surging Seismic interferometry holds substantial potential for revealing dynamic englacial and subglacial processes