American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 1312392 bytes)    Cited by

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, F03015, doi:10.1029/2007JF000925, 2008

Dynamic controls on glacier basal motion inferred from surface ice motion

Ian M. Howat

School of Earth Sciences and Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, USA


Slawek Tulaczyk

Department of Earth and Planetary Sciences, University of California, Santa Cruz, California, USA


Edwin Waddington

Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA


Helgi Björnsson

Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland


Abstract

Current heuristic laws that relate the motion of glaciers due to sliding along the bed to the subglacial water pressure fail to reproduce variations in sliding speed on timescales of specific hydrologic events, such as lake drainage, rainfall, or surging. This may be due to the importance of subglacial cavity evolution and shifts in the glacier stress field, both of which are not accounted for in typical sliding laws. We use multiple time series of surface motion over a 66-day period at Breiðamerkurjökull, Iceland, to infer changes in bed separation and longitudinal force budget. We observe multiple, distinct periods of increased surface motion and uplift corresponding to periods of rainfall and/or increased temperatures. We find consistent hysteresis and lags between motion and variations in both the bed separation and longitudinal stress gradient that we attribute to the redistribution of normal stresses at the bed during cavity growth. Increases in the longitudinal stress gradient suggest a downglacier stress transfer during increased basal motion that is consistent with increased drainage system efficiency toward the terminus. Our results suggest that the transient evolution of the subglacial drainage system and shifts in the glacier stress field are important controls on basal motion.

Received 23 October 2007; accepted 1 May 2008; published 13 August 2008.

Keywords: Glacier; sliding; dynamics.

Index Terms: 0774 Cryosphere: Dynamics; 0776 Cryosphere: Glaciology (1621, 1827, 1863); 0720 Cryosphere: Glaciers; 0762 Cryosphere: Mass balance (1218, 1223).

Read Full Article (file size: 1312392 bytes)    Cited by

Citation: Howat, I. M., S. Tulaczyk, E. Waddington, and H. Björnsson (2008), Dynamic controls on glacier basal motion inferred from surface ice motion, J. Geophys. Res., 113, F03015, doi:10.1029/2007JF000925.