Seismicity, seawater and seasonality: new insights into iceberg calving from Yahtse Glacier, Alaska

• Main Author: Bartholomaus, Timothy Chester
• Other Authors: Larsen, Christopher, O’Neel, Shad, Pettit, Erin, Truffer, Martin, West, Michael
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2013
• Subjects: Fairbanks; Gulf of Alaska; glacier; glaciers; Alaska
• Online Access: http://hdl.handle.net/11122/4461

Dissertation (Ph.D.) University of Alaska Fairbanks, 2013 At many of the largest glaciers and ice sheets on Earth, more than half of the annual ice loss occurs through iceberg calving into the ocean. Calving is also responsible for the most rapid ice mass changes, both directly (through the mechanical loss of ice at the terminus) and indirectly (through dynamic thinning of upstream ice initiated by terminus retreat). Yet, the mechanisms and factors that control calving are poorly understood. Recordings of glaciogenic seismic waves, known as "icequakes," produced during iceberg calving offer opportunities for insight that cannot be gleaned through other methods. In order to better understand iceberg calving and its links to calving icequakes, we conducted a 2-yr study of rapidly advancing Yahtse Glacier, site of one of the densest clusters of calving icequakes in southern Alaska. By synchronizing video of iceberg calving events with locally-recorded seismograms, we found that most icequake energy is produced after subaerial iceberg detachment from the glacier terminus, while the iceberg impacts and descends below the sea surface. Cavitation beneath the water surface generates the largest amplitude portions of icequakes-those that are detectable over several hundred km distances. Numerical simulations of these iceberg-sea surface interactions predict sources with durations that are consistent with the 1-5 Hz frequency content of calving icequakes. Oceanographic measurements in Icy Bay, where Yahtse Glacier terminates, reveal that warm water may melt most of the ice reaching the submarine terminus. During the summer, water with temperature > 10 °C flows from the Gulf of Alaska coast to within 2 km of Yahtse Glacier's terminus. We find that heat transport between 5 and 40 x 109 W can readily melt the submarine glacier terminus at a rate that matches the speed with which ice flows towards the glacier terminus (17 m d⁻¹). Subaerial iceberg calving rates may be paced by submarine melt rates. To place our calving ...