Seismological Investigation of Columbia Glacier Calving Mechanics

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

ABSTRACT OPP-024072 Pfeffer Iceberg calving is a major component of mass loss from many marine glaciers and is intimately connected with the dynamics of tidewater glacier retreat. Despite its importance, the calving process is very poorly understood. The need to understand calving and tidewater glacier dynamics becomes more pressing as the importance of Alaskan glaciers in modern global mass balance is better understood, and as the utility of modern tidewater glaciers as analogs for rapid retreat of marine-based paleo ice sheets is recognized. The Columbia Glacier has been studied since the early 1980's, and has yielded a large volume of very useful data. The importance of studying Columbia Glacier increases, however, as its retreat accelerates. It is the last of Alaska's major tidewater glaciers to retreat from its extended position, and currently the world's fastest glacier (at 12 km yr-1), which discharges approximately 22 km3 per year of ice into the ocean via calving, and may complete its retreat within 25 years or less. The Principal Investigator will pursue three objectives: 1) a detailed analysis of kinematics determined from the 1997- 1999 photography which describes the flow regime, strain rate characteristics, boundary tractions, and bed depth in the glacier channel within about four km of the terminus will be done. Geostatistical analysis of spatial heterogeneity of strain rates in the lowest five km of the glacier, based on terrestrial photogrammetry from 1999 ground-based photography will be completed. This work will be supplemented by additional aerial photography from 2000 and 2001. Theoretical analysis of upstream propagation of kinematic waves associated with irreversible tidewater retreat which shows how basal sliding may be the ultimate cause of the episodic and generally irreversible character of tidewater retreat will be addressed; 2) Observations of glacial icequake and calving activity using modern seismic recording equipment is relatively immature. The Principal Investigator will analyze these data sets to develop techniques that will improve future deployment and data analysis. The goal is to determine first-order time and frequency domain source characteristics, using known seismic sources. He will also digitize the smoked-paper records to enable analysis in standard software packages and apply the refined event detection software to the digitized data set; and 3) The August 2002 photo flights are the 124th and 125th flights in an unbroken series of aerial photography started in 1976, and from which most of our knowledge on the pattern of retreat since around 1980 is based. Future photogrammetric analysis now becomes his responsibility because the photogrammetric procedures are fairly straightforward, but the actual process of recognizing the correct features in the photography is not. Thus, the most difficult part of the problem is suited to the skills of a glaciologist than a photogrammetrist, so he will purchase new digital ('softcopy') photogrammetric software.