HR: 11:05h
AN: V12B-04 INVITED     [Abstracts]
TI: What`s it Tuya: Ice Thickness Determined From H₂O Contents Measured in Glasses From Subglacial Volcanoes in British Columbia and Iceland
AU: * Cameron, B I
EM: bcameron@uwm.edu
AF: Univeristy of Wisconsin-Milwaukee, Department of Geosciences, P.O. Box 413, Milwaukee, WI 53201-0413 United States
AU: Roggensack, K
EM: kurt.roggensack@asu.edu
AF: Arizona State University, Department of Geological Sciences, Box 871404, Tempe, AZ 85287-1404 United States
AU: Boscov, S
EM: snejanab@wi.rr.com
AF: Univeristy of Wisconsin-Milwaukee, Department of Geosciences, P.O. Box 413, Milwaukee, WI 53201-0413 United States
AU: Peterson, A H
EM: ahp@uwm.edu
AF: Univeristy of Wisconsin-Milwaukee, Department of Geosciences, P.O. Box 413, Milwaukee, WI 53201-0413 United States
AB: Classic exposures of flat-topped subglacial volcanoes called tuyas exist in northern British Columbia and Iceland. In northern British Columbia, Ash Mountain, South Tuya, and Three Caribou Tuya are basaltic scoria cones that began eruptive activity under glacial ice during the Fraser glaciation (25 to 10 ka). In Iceland, Hlödufell, Raudafell, and Efstadalsfjall were erupted beneath ice caps in the western neovolcanic rift zone. In general, sections of the basaltic subglacial volcanoes reveal a stratigraphic progression from pillow lavas to hyaloclastite deposits from the base upward. Locally, the sections are capped by subaerial basaltic lava flows. Glass samples were extracted from pillow basalts, pillow breccias, and hyaloclastites in order to measure their H₂O content. Generally, British Columbia tuyas have higher magmatic H₂O contents (0.42-0.66 wt%) than the Icelandic tuyas (0.14-1.24 wt%). More interestingly, H₂O contents decrease with elevation at tuyas in British Columbia, whereas at Hlödufell and Efstadalsfjall in Iceland, H₂O contents increase with elevation. For example, at Ash Mountain in British Columbia, pillow basalts have higher H₂O contents (0.54-0.66 wt%) than associated hyaloclastite deposits (0.43-0.48 wt%). In contrast, at Hlödufell in Iceland basal pillow basalts have lower H₂O contents (0.14-0.22 wt%) than the overlying hyaloclastites (0.28-0.29 wt%). The preliminary data from British Columbia support eruptive models where pillow basalts erupted under thicker ice/deeper water than hyaloclastite deposits. Moreover, the measured H₂O contents can be used to constrain the thickness of ice overlying the scoria cones at the time of eruption. Assuming a basaltic composition of 49 wt% SiO₂ and an ice density of 0.9 g cm^-3, the ice at Ash Mountain was up to 453 m thick during extrusion of the pillows, but thinned to 215 m for the eruption of the hyaloclastites. At Efstadalsfjall in Iceland, overlying ice thickened from 79 m to 204 m during the course of the eruption.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 8404 Volcanoclastic deposits
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005