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Volcano study helps measure historic ice sheet thickness

UBC geologists examine pyroclastic deposits near summit of tephra cone on south side of Kima'Kho. Key attributes of these deposits established that they were deposited above the level of a surrounding englacial lake.

UBC geologists examine pyroclastic deposits near summit of tephra cone on south side of Kima’Kho. Key attributes of these deposits established that they were deposited above the level of a surrounding englacial lake. Photo courtesy UBC Science.

Ancient tuyas hold climate clues

By Summit Voice

FRISCO —In what must have been incredible displays of fire and ice, ancient volcanoes once erupted under massive glacial ice sheets, leaving deposits that could help paleoclimatologists unravel some ice age puzzles.

In a recent study, University of British Columbia researchers surveyed those deposits at the Kima’ Kho tuya, which erupted under an ice sheet about 1.8 million years ago. Their findings suggest that he ancient regional ice sheet through which the volcano erupted was twice as thick as previously estimated.

“At Kima’Kho, we were able to map a passage zone in pyroclastic deposits left by the earliest explosive phase of eruption, allowing for more accurate forensic recovery of paleo-lake levels through time and better estimates of paleo-ice thicknesses,” says UBC volcanologist James K Russell, lead author on the paper published this week in Nature Communications.

Subglacial eruptions generate distinctive deposits indicating whether they were deposited below or above the waterline of the englacial lakes–much like the rings left on the inside of a bath tub. The transitions from subaqueous from subaerial deposits are called passage zones and define the high stands of englacial lakes. The depth and volume of water in these ephemeral lakes, in turn, gives researchers an accurate measure of the minimum palaeo-ice thicknesses at the time of eruption.

“Applying the same technique to other subglacial volcanos will provide new constraints on paleoclimate models that consider the extents and timing of planetary glaciations, Russell said.”

While relatively rare globally, tuyas are common throughout Iceland, British Columbia, Oregon, and beneath the Antarctic ice-sheets. Kima’Kho tuya forms a high relief structure covering 28 square kilometres rising 1,946 metres above sea level on the Kawdy Plateau near Dease Lake. The plateau hosts six other tuyas.

“We hope our discovery encourages more researchers to seek out pyroclastic passage zones,” says Lucy Porritt, a Marie Curie Research Fellow at UBC and University of Bristol. “With more detailed mapping of glaciovolcanic sequences, and the recognition of the importance of these often abrupt changes in depositional environment, our understanding of glaciovolcanic eruptions and the hazards they pose can only be advanced.”

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