CGRG Bibliography of Canadian Geomorphology
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Author : Edwards, B.R.; Russel, J.K.; Anderson, R.G.; and Villeneuve, M.
Date : 1999.
Title : Punctuated, peralkaline, subglacial volcanism at Hoodoo Mountain Volcano, Northwestern British Columbia, Canada
Publication : 1999 Fall Meeting of the American Geophysical Union, December 13-17, 1999 , San Francisco, California (abstract).
Issue :
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Abstract
Hoodoo Mountain volcano is located in northwestern British Columbia, 100 km south of the Mount Edziza volcanic complex, and 300 km southeast of Mount Edgecumbe, Alaska. The summit of the volcano (1800 m) is covered by a small icecap, which is 3 km in diameter; the base of the volcano is 6 km in diameter. Hoodoo Mountain volcano is a complex edifice comprising, in stratigraphic succession: a) multiple sequences of ice-dammed, highly-jointed, aphanitic lava flows and thick, monolithologic volcanic breccias; b) subaerial, partly welded to strongly eutaxitic pyroclastic flow deposits; c) subaerial, aphanitic to slightly porphyritic lava flows and associated breccias; d) subglacial deposits of hyaloclastite and non-fragmental, highly jointed, aphanitic lava; and e) subaerial, highly porphyritic lava flows. The morphology of the volcano is distinctive and is a result of direct (subglacial eruptions) and indirect (glacial erosion) interaction with glacial icesheets. Subglacial and englacial eruptions of lava early in the eruptive history of Hoodoo Mountain were dammed by surrounding valley glaciers; such dammed lava flows formed cliffs that circumnavigate the volcano. Several of the cliffs are in excess of 200 m high. Preliminary, high precision, Ar-Ar dating of samples from the lower, cliff-forming units suggest that the volcano was surrounded by ice at approximately 85-80 ka, during its initial stages of volumetrically significant eruptions. A major episode of pyroclastic activity is bracketed stratigraphically to be between 80 and 54 ka. A second major period of subglacial eruptions occurred between 40 and 30 ka. The final eruptive episode, which appears to have been dominated by subaerial eruptions, began at approximately 28 ka and lasted until 9-10 ka. With an estimated volume of 17 cubic km, Hoodoo Mountain is the smallest of three peralkaline volcanic centers in the Northern Cordilleran Volcanic Province of northwestern Canada. All of the lavas erupted from Hoodoo contain phenocrysts of alkali feldspar, Fe-rich clinopyroxene, and magnetite. Nepheline has been qualitatively identified only as a groundmass phase. Samples from near the base of the volcano are generally fine-grained, with less than 5% phenocrysts by volume. Near the upper part of the edifice, lavas become more enriched in phenocrysts, culminating with highly porphyritic, subaerial lava flows, which commonly contain up to 30\% by volume of alkali feldspar megacrysts, hedenbergitic clinopyroxene phenocrysts, magnetite phenocrysts, and glomerocrysts of all three phenocryst phases. All of the Hoodoo lava samples analyzed to date (N=48) are classified as either trachytes or phonolites on the standard TAS classification, are nepheline and acmite normative, and are extremely enriched in FeO relative to MgO.
Bibliography of Canadian Geomorphology