Distribution, composition, and source of the White River Ash, Yukon Territory

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Lerbekmo, J. F., Campbell, F. A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1969
• Subjects: General Earth and Planetary Sciences; Yukon; Klutlan Glacier; glacier; Alaska
• Online Access: http://dx.doi.org/10.1139/e69-011; http://www.nrcresearchpress.com/doi/pdf/10.1139/e69-011

The White River Ash is a bi-lobate 1500 year old deposit occupying at least 6 cubic miles and covering some 125 000 square miles of southern Yukon and eastern Alaska. Sixty-six samples were collected at 5-mile intervals, principally along two traverses 120 miles apart across the main lobe, and subjected to X-ray fluorescence and petrographic analysis.The ash is a rhyodacite composed of glass (n = 1.502), andesine, hornblende, hypersthene, and magnetite. The average chemical composition is SiO 2 = 67.4, Al 2 O 3 = 15.1, TiO 2 = 0.5, MgO = 2.0, FeO = 2.0, Fe 2 O 3 = 2.2, Na 2 O = 4.1, K 2 O = 2.5 and CaO = 4.1, but there is a significant difference between the two traverses owing to the increase in glass relative to crystal components downwind.A synthesis of the distribution of the ash permitted the drawing of a 5 by 12 miles 'target' source rectangle in the St. Elias Range between Mts. Natazhat and Bona in Alaska. Aerial photographs revealed a suspect mound 0.4 miles in diameter beside the Klutlan Glacier. Access by helicopter showed the mound to be a flat cone of large White River pumice fragments. It is believed that the vent lies beneath the glacier next to the cone.