Show simple item record

dc.contributor.authorBartholomaus, Timothy Chester
dc.date.accessioned2014-10-10T19:21:38Z
dc.date.available2014-10-10T19:21:38Z
dc.date.issued2013-12
dc.identifier.urihttp://hdl.handle.net/11122/4461
dc.descriptionDissertation (Ph.D.) University of Alaska Fairbanks, 2013
dc.description.abstractAt 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 and submarine melt observations in a broader temporal context, we construct an empirical model of iceberg size using icequake properties and tune the model with over 800 visually-observed iceberg calving events. We find that iceberg calving is at its minimum during the winter, when seawater is cool and mixing of proglacial seawater by subglacial discharge is weak. Overlaying this long period cycle, we find significant daily to inter-annual variability and sensitivity of calving to tidal stage. These observations expand our appreciation for the ocean's important role in iceberg calving: at time scales ranging from the sub-second generation of icequakes, to the annual undercutting of the glacier terminus.en_US
dc.description.tableofcontentsChapter 1. Introduction -- Chapter 2. Calving seismicity from iceberg-sea surface interactions -- Chapter 3. Does calving matter? Evidence fro significant submarine melt -- Chapter 4. Observing iceberg calving flux at a grounded tidewater glacier with passive seismology -- Chapter 5. Conclusions.
dc.language.isoen_USen_US
dc.titleSeismicity, seawater and seasonality: new insights into iceberg calving from Yahtse Glacier, Alaskaen_US
dc.typeDissertationen_US
dc.type.degreephden_US
dc.identifier.departmentDepartment of Geology and Geophysicsen_US
dc.contributor.chairLarsen, Christopher
dc.contributor.committeeO’Neel, Shad
dc.contributor.committeePettit, Erin
dc.contributor.committeeTruffer, Martin
dc.contributor.committeeWest, Michael
refterms.dateFOA2020-03-05T08:53:57Z


Files in this item

Thumbnail
Name:
Bartholomaus_uaf_0006E_10095.pdf
Size:
28.35Mb
Format:
PDF
Thumbnail
Name:
2S1_Block_calving.mov
Size:
28.35Mb
Format:
QuickTime video
Thumbnail
Name:
2S2_Flake_calving.mov
Size:
28.35Mb
Format:
QuickTime video
Thumbnail
Name:
3S1_IcyBay_time_lapse.mov
Size:
28.35Mb
Format:
QuickTime video

This item appears in the following Collection(s)

Show simple item record