Publications

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2009
Fricker, HA, Scambos T.  2009.  Connected subglacial lake activity on lower Mercer and Whillans Ice Streams, West Antarctica, 2003-2008. Journal of Glaciology. 55:303-315. AbstractWebsite

We examine patterns of localized surface elevation change in lower Mercer and Whillans Ice Streams, West Antarctica, which we interpret as subglacial water movement through a system of lakes and channels. We detect and measure the lake activity using repeat-track laser altimetry from ICESat and image differencing from MODIS image pairs. A hydrostatic-potential map for the region shows that the lakes are distributed across three distinct hydrologic regimes. Our analysis shows that, within these regimes, some of the subglacial lakes appear to be linked, with drainage events in one reservoir causing filling and follow-on drainage in adjacent lakes. We also observe changes near ice raft 'a' in lower Whillans Ice Stream, and interpret them as evidence of subglacial water and other changes at the bed. The study provides quantitative information about the properties of this complex subglacial hydrologic system, and a relatively unstudied component of ice-sheet mass balance: subglacial drainage across the grounding line.

2007
Fricker, HA, Scambos T, Bindschadler R, Padman L.  2007.  An active subglacial water system in West Antarctica mapped from space. Science. 315:1544-1548.   10.1126/science.1136897   AbstractWebsite

Satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of Whillans and Mercer ice streams, West Antarctica, reveal 14 regions of temporally varying elevation, which we interpret as the surface expression of subglacial water movement. Vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing. A major, previously unknown subglacial lake near the grounding line of Whillans Ice Stream is observed to drain 2.0 cubic kilometers of water into the ocean over similar to 3 years, while elsewhere a similar volume of water is being stored subglacially. These observations reveal a widespread, dynamic subglacial water system that may exert an important control on ice flow and mass balance.

Bassis, JN, Fricker HA, Coleman R, Bock Y, Behrens J, Darnell D, Okal M, Minster JB.  2007.  Seismicity and deformation associated with ice-shelf rift propagation. Journal of Glaciology. 53:523-536.   10.3189/002214307784409207   AbstractWebsite

Previous observations have shown that rift propagation on the Amery Ice Shelf (AIS), East Antarctica, is episodic, occurring in bursts of several hours with typical recurrence times of several weeks. Propagation events were deduced from seismic swarms (detected with seismometers) concurrent with rapid rift widening (detected with GPS receivers). In this study, we extend these results by deploying seismometers and GPS receivers in a dense network around the tip of a propagating rift on the AIS over three field seasons (2002/03, 2004/05 and 2005/06). The pattern of seismic event locations shows that icequakes cluster along the rift axis, extending several kilometers back from where the rift tip was visible in the field. Patterns of icequake event locations also appear aligned with the ice-shelf flow direction, along transverse-to-rift crevasses. However, we found some key differences in the seismicity between field seasons. Both the number of swarms and the number of events within each swarm decreased during the final field season. The timing of the slowdown closely corresponds to the rift tip entering a suture zone, formed where two ice streams merge upstream. Beneath the suture zone lies a thick band of marine ice. We propose two hypotheses for the observed slowdown: (1) defects within the ice in the suture zone cause a reduction in stress concentration ahead of the rift tip; (2) increased marine ice thickness in the rift path slows propagation. We show that the size-frequency distribution of icequakes approximately follows a power law, similar to the well-known Gutenberg-Richter law for earthquakes. However, large icequakes are not preceded by foreshocks nor are they followed by aftershocks. Thus rift-related seismicity differs from the classic foreshock and aftershock distribution that is characteristic of large earth quakes.

2000
Fricker, HA, Hyland G, Coleman R, Young NW.  2000.  Digital elevation models for the Lambert Glacier-Amery Ice Shelf system, East Antarctica, from ERS-1 satellite radar altimetry. Journal of Glaciology. 46:553-560.   10.3189/172756500781832639   AbstractWebsite

The Lambert Glacier-Amery Ice Shelf system is a major component of the East Antarctic ice sheet. This paper presents two digital elevation models (DEMs) that have been generated for the Lambert-Amery system from validated European Remote-sensing Satellite (ERS-1) radar altimeter waveform data. The first DEM covers the Amery Ice Shelf only, and was produced using kriging on a 1 km grid. The second is a coarser (5 km) DEM of the entire Lambert-Amery system, generated via simple averaging procedures. The DEMs provide unprecedented surface elevation information for the Lambert-Amery system and allow new insight into the glaciology of the region.