Englacial lake dynamics within a Pleistocene Cordilleran ice sheet at Kima' Kho tuya (British Columbia, Canada)

February 4, 2022
Kima' Kho tuya (photo: UBC Science)

Kelly RussellBenjamin Edwards, Marie Turnbull and Lucy Porritt

Kima' Kho tuya is a Pleistocene (1949 ± 63 ka) (ka: kilo annum; one thousand years) glaciovolcano in the northern Cordillera of British Columbia. In a new EOAS research published in Quaternary Science Reviews, Professor Kelly Russell and his co-authors, Benjamin Edwards (Dickinson College), Marie Turnbull and Lucy Porritt, reconstructed the englacial lake dynamics attending the volcanic evolution and growth of Kima' Kho volcano, including a massive, catastrophic deluge.

Volcanic eruptions, when interacting with the cryosphere (i.e., snow, ice, firn, permafrost, and meltwater), produce edifice morphologies and deposit lithofacies that directly reflect their eruption environment. These glaciovolcanoes represent a proxy for local and global paleoclimates and they are the only evidence of ancient ice masses coinciding with the time and location of the eruption in many cases.

“Passage zones” are stratigraphic surfaces found in littoral settings separating volcanic deposits diagnostic of subaqueous environments from overlying sequences of subaerial deposits. In glaciovolcanic settings, these surfaces are important because they unequivocally record the heights and depths of sustained within-ice lakes of meltwater (i.e. syn-eruptive englacial lakes), thereby informing on the presence and nature of the enclosing ice sheet.

Passage zones preserved in Kima' Kho edifice. Panel 1: Field photograph of Kima' Kho tuya looking to the west. Panel 2: Corresponding geological cross-section showing projected distribution of the main volcanic lithofacies defining several passage zones (1-3). Panel 3: Stratigraphic logs showing lithofacies variations used to define three separate passage zones (PZ: 1-3) and their elevations.
Definition of the term “passage zone”. Cartoon from Jones (1968) shows the formation of passage zones in glaciovolcanic environment and field photograph shows one of the passage zones preserved at Kima’ Kho where lavas erupted into a dry environment have flowed over and capped contemporaneous pillow-lava breccia beds that are deposited in a deep englacial lake of meltwater.

Kima' Kho is unique as it is one of only a few well-documented tuyas that hosts multiple and diverse passage zones. Three temporally distinct passage zones record the interplay between growth of the volcanic edifice, syn-volcanic melting of the enclosing ice sheet, and fluctuations in the depth of the englacial lake. The earliest passage zone (PZ1) was formed during the initial explosive phase of eruption when the tephra cone became emergent from the 340 m deep englacial lake. Two subsequent passage zones (PZ2-3) occur at lower elevations, indicating a major draining of the englacial lake followed by refilling to depths of 230-180 m and 260-280 m, respectively. The substantial decline in lake level between PZ1 and PZ2 suggests a massive, catastrophic deluge (i.e. jökulhlaup) of 1-2 km3. Lastly, the reconstructed glaciovolcanic evolution of Kima' Kho demands the presence of a regionally extensive ice sheet overlying the Kawdy plateau at ~1.9 Ma and representing an earlier incarnation of the Cordilleran Ice Sheet (CIS).

Passage zones preserved in Kima' Kho edifice. Panel 1: Field photograph of Kima' Kho tuya looking to the west. Panel 2: Corresponding geological cross-section showing projected distribution of the main volcanic lithofacies defining several passage zones (1-3). Panel 3: Stratigraphic logs showing lithofacies variations used to define three separate passage zones (PZ: 1-3) and their elevations.
Passage zones preserved in Kima' Kho edifice. Top panel: Field photograph of Kima' Kho tuya looking to the west. Middle panel: Corresponding geological cross-section showing projected distribution of the main volcanic lithofacies (Lt1/Lt2: subaqueously and subaerially deposited lapilli tuffs representing an explosive onset to the eruption. Tb1-3: subaqueously deposited and steeply inclined beds of tuff breccia dominated by pillow lava fragments. L1-3: stacked sheets of subaerial pahoehoe lavas) defining several passage zones (1-3). Bottom panel: Stratigraphic logs showing lithofacies variations used to define three separate passage zones (PZ: 1-3) and their elevations.
Conceptual summary model for the temporal evolution of Kima' Kho volcano and associated englacial lake.
Conceptual summary model for the temporal evolution of Kima' Kho volcano and associated englacial lake.