UBC Undergraduate Research

History and Dynamics of Explosive Volcanism at Tseax Cone, British Columbia Gallo, Rose

Abstract

The eruption of Tseax Cone, approximately 320 years ago, is thought to be the deadliest volcanic eruption in Canadian history, resulting in the deaths of an estimated 2000 people. This small eruptive center in northern British Columbia comprises two cinder cones, a highly dissected spatter cone, a tephra deposit covering an approximate area of 2.2 x 10⁷ m², and a 32 km long lava flow. New geochemical, paleomagnetic, petrographic and field data are drawn upon to propose a new hypothesis that all eruptive materials at Tseax were produced during a single period of activity. The eruptive sequence is shown to begin with low energy fire fountaining forming a small cinder cone approximately 60 m in diameter and a spatter cone 460 m in diameter. Higher energy fountaining activity from a new vent, slightly offset within the spatter cone, and the production of a tephra column slightly more than 5 km high and lasting for approximately one day followed the first eruptive phase. The high energy phase produced a larger cinder cone and a highly asymmetric, northeast elongate, tephra deposit. The final phase of the eruption was the extrusion of the lava flow accompanied by a final sputtering of ballistics from the main vent.

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