Intellectual merit. The Principal Investigators will study both ongoing and historical changes in dynamics at the rapidly retreating Columbia Glacier, in south central Alaksa. Tidewater glaciers (TWGs) like Columbia Glacier terminate in the ocean and merit special attention because they exhibit some of the largest and strongly non-linear dynamic volume changes of all glaciers worldwide. In addition, most ice sheet mass loss occurs at marine-ending outlet glaciers that display dynamic instabilities very similar to TWG. Yet, the response of these glaciers to climate forcing remains very poorly understood. They will continue an unmatched 30-year record of observations at Columbia Glacier and to study the similarities between it and the rapidly retreating Greenland outlet glaciers. Project goals are aimed at a predictive capability for future TWG volume changes, which are a dominant constituent of global sea level rise. A variety of measurements including vertical aerial photogrammetry (and subsequent feature-tracking), terrestrial time-lapse photogrammetry, airborne radar, GPS surveying, and meteorological monitoring will provide robust constraints for both inverse and forward modeling of the stress and flow fields. The need for a better understanding of the interaction between climate forcing, glacier dynamics and ice volume change is widely recognized and has led to recommendations for better glacier observations in the the IPCC 2007 Summary for Policymakers, the SEARCH Implementation Plan, the IPY E.U. initiative GLACIODYN, and the NSF call for an Arctic Observing Network. Both the SEARCH Implementation Plan and GLACIODYN list Columbia Glacier specifically as a key glaciological site. This study strongly aligned with the goals of GLACIODYN, and has been endorsed by the steering committee.
Broader impacts. Because of their large numbers, small glaciers still dominate the cryosphere's contribution to global sea level rise. The largest uncertainties in this contribution are from TWG where volume changes are controlled by unmeasured and poorly understood dynamical processes. Rapid freshwater inputs of glaciers and ice sheets directly affect ocean currents, and catastrophic retreats have affected global climate, as evidenced through Heinrich Events. Regional and local changes from rapid volume change at TWGs affect fjord geometry and circulation while exposing new landmass, which causes large changes in terrestrial ecosystems including some of the strongest observed isostatic rebound signals. This study will create new partnerships through collaborations with European colleagues interested in advancing terrestrial photogrammetric methodology, and through a forward modeling collaboration with A. Vieli. The activity is a collaboration between researchers from the Universities of Colorado and Washington, and has a strong educational component, involving undergraduates, and two graduate students. Outreach will occur through channels offered by INSTAAR and National Snow and Ice Data Center (NSIDC), local outreach activities conducted by the Principal Investigators in Valdez, Alaska and University of Washington. Data will be provided to the GLACIODYN outreach coordinator, who will use Virtual Globe technology for project visualization. Results will appear in peer reviewed journals, presentations at national and international meetings, and small workshops focusing on software and algorithm development, and will be archived at NSIDC and UNAVCO
Summary: The primary focus of the project is the historical and ongoing change at the ocean-terminating and rapidly retreating Columbia Glacier, which is located in south-central Alaska’s Prince William Sound. The best recent estimates of mass loss from Alaskan glaciers range from 60-100 GT/yr, which is on par with discharge of the Greenland Ice Sheet. Columbia Glacier discharges ca. 4-7 GT/yr to the ocean, and is the only ocean-terminating glacier in Alaska with a long-term record of discharge, and one of the few glaciers in Alaska with any long-term measurement program of any kind. Ocean-terminating, or tidewater, glaciers (TWGs) merit special attention because they are among the most strongly non-linear dynamic glacier systems in the world, which means they can rapidly transfer large quantities of ice directly to the ocean. This capacity makes them the largest contributors to the new mass, or eustatic component of global sea level rise. Our research is designed to provide valuable insight into the stability of both the TWG and the ice sheet outlet glaciers. Our work continued the acquisition of a 30-year record of photogrammetrically-determined surface topography and velocities (achieved with vertical photography and continuous ground-based time lapse observations). We are also conducting a variety of ground-based experiments, including seismic observations of calving, high-rate time lapse observations of calving, high-rate GPS and optical survey measurements of surface speed, laser scanning of the calving front, and meteorological observations. During this project we developed a new and low cost method to derive surface topography of the glacier from oblique aerial photography and transitioned from aerial photography to spaceborne radar images to quantify glacier motion. One of the principal results of our efforts was a quantitative description of the mechanical changes in the fracture mechanism for iceberg formation when the terminus transitioned from grounded to floating conditions and vice-versa. This type of transition had never been directly observed or measured. This project had widespread impacts. Graduate student and young investigator training was central to our work; we trained both American and foreign graduate students, supported two post-doctoral researchers and partially supported two young investigators. We developed strong international collaborations with multiple nations, strengthening the cohesiveness of the global research effort aimed to understand calving glaciers and their impact on the global sea level budget. Our team worked closely with the extreme Ice Survey on outreach issues. Products from these efforts include ongoing video displays in the Denver International Airport (with audiences in the millions), 2 television documentaries, and 2 books intended for the public. Each investigator has delivered high profile lectures for general audiences surrounding the topics of our research and its connections with global change.
