Mount Edziza Volcanic Complex (MEVC) lies within the Northern Cordilleran Volcanic Province (NCVP), in northwest British Columbia, Canada. The eruption products have been emplaced in a variety of subaerial, sub-ice and subaqueous environments from about 8Ma to less than 2000 y.b.p. (Souther, 1992). Ice Peak Formation (IPF) trachyte lava flows of approximately 1Ma age (Souther, 1992) are exposed at Ornostay Bluff (OB) and Koosick Bluff (KB). These flows comprise basal flow breccias overlain by massive conchoidally-fractured lava with large, poorly-developed columns, and local flow banding. Edziza Formation (EF) approximately 1Ma (Souther, 1992) phonolite is exposed at Triangle Dome (TD). TD can broadly be divided into an upper and lower zone. The upper zone comprises poorly-developed columns in addition to prominent jointing. In the lower zone the columns are planar and 75cm-3m-wide in the interior of the complex grading into fan-like and curved subhorizontal columns <75cm-wide in the outer margins of the lower zone. The upper zone is interpreted as an entablature where slow cooling was overprinted by joints formed during abrupt cooling due to water ingress. Local areas with well-developed columnar jointing in the upper zone may reflect endogenous growth by late-stage intrusive emplacement, or areas where water ingress was less efficient. The lower zone is interpreted as a lower colonnade with slower cooling and less water ingress during cooling. The fan-like columns in the outer margins of the lower zone reflect cooling by direct contact with curved margins of the ice cavity. The estimated minimum thickness of the ice-contact zone is ~60m reflected by the thickness of the lower zone. Identifying ice-contact structures in trachytic-phonolitic lavas is difficult, especially in glacially eroded examples such as OB and KB, where marginal cooling-columns and structures caused by direct contact with ice have been eroded. Trachyte lavas display a wide range of viscosities, flow thicknesses, and aspect ratios therefore caution is required in interpreting overthick flows as having formed by confinement by former ice. Studies that focus on comparisons of estimated flow velocities and rates of ice melting are useful, though there are numerous unaccounted for variables in these models.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08032008-221140 |
| Date | 28 September 2008 |
| Creators | LaMoreaux, Kristen |
| Contributors | Dr. Ian Skilling, Dr. Thomas Anderson, Dr. Michael Ramsey |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08032008-221140/ |
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