T65 Multidisciplinary Studies of Cascade Volcanism and its Tectonic Setting II

Sunday, 18 October 2009
1:30 PM - 5:30 PM
E143/144

MORPHOLOGY OF MOUNT BAKER'S CARMELO (SUMMIT) CRATER REVEALED BY ICE-PENETRATING RADAR

Paper number: T65-8
Program: Technical Sessions
Time: 3:15 PM – 3:30 PM

Authors

Abstract

Ice-filled Carmelo Crater underlies the summit plateau of Mount Baker (3286 meters), a composite volcano in northwest Washington State. The nearly flat plateau was traversed on foot with ice-penetrating radar to determine ice thickness and dimensions of the crater. The resulting profile shows that the crater is a cup-shaped depression with a maximum depth of approximately 82 meters. Its east-west dimension of about 470 meters spans the full width of the summit plateau. The summit of the mountain, Grant Peak, is a scoria mound on the eastern margin of the crater rim. Carmelo Crater was the focus for Pleistocene edifice-building eruptions, after which activity shifted in the Holocene to the active satellite, Sherman Crater, on the south flank.

Our mountaineering team used a mono-pulse transmitter (silicon-controlled rectifier), a Tektronix 222 digital oscilloscope that recorded two-way travel time and the amplitude of reflections within the ice, laptop computer, and dipole antennae (f=300W) with center frequencies of 7 MHz. Measurements were made at 20 meter intervals across the nearly level ice plateau.

We calculated ice thickness by assuming a radio wave speed of 168m/μs through the ice. Uncertainties in ice thickness were estimated to be ±5 meters, given possible errors in migration (a technique used to find the true thickness vertically beneath each point), bed reflections, and wave velocity.

Crater morphology could have hazards implications in the event of increased thermal activity at the summit. Oblique aerial photos taken at the end of the summer snow melt season show a fragmental deposit exposed along the outer margin of the ice cap that is believed to correspond to the scoria-draped rim of Carmelo Crater. Roosevelt Glacier has at least partially breached this deposit on the crater’s north rim, although crevasses prevented the team from determining the breach extent. If the crater is not completely breached, melt water could pond and potentially overflow to send floods down the inhabited Glacier Creek and North Fork Nooksack River valleys.