THE MECHANICS OF SUBGLACIAL BASALTIC LAVA FLOW EMPLACEMENT: INFERRING PALEO-ICE CONDITIONS

• Main Author: Hungerford, Jefferson D. G.
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Canada; British Columbia; Mount Edziza; Ice Sheet
• Online Access: http://d-scholarship.pitt.edu/20197/; http://d-scholarship.pitt.edu/20197/10/Hungerfordjdg_etd2013_v2.1.pdf

Recent studies of terrestrial glaciovolcanic terrains have elucidated the utility of volcanic deposits as recorders of ice conditions at the time of eruption. Practically all of these investigations, however, have focused upon the associations of volcaniclastic and coherent lava lithofacies at or proximal to the source vent. Very few studies have documented the emplacement of effusion-dominated, basaltic glaciovolcanic eruptions and their distal deposits that more accurately reveal paleo-ice conditions. Both Mauna Kea volcano, Hawaii and the Tennena volcanic center (TVC), on Mount Edziza, British Columbia, Canada, preserve records of interaction between coherent lavas and an ice sheet inferred to be associated with the last glacial maximum (LGM). The identification, mapping and description of subglacial TVC lava flows reveals the spatial distribution and characteristics of primary volcanic lithofacies and associated glaciogenic lithofacies, and reveals the processes of the emplacement of the distal lava flows under thick ice. Exposure dating with cosmogenic nuclides proves the most effective technique to temporally constrain the emplacement of these subglacial lavas. This work shows; 1) classification schemes that utilize remotely sensed imagery are locally robust but are not readily viable as identifiers of subglacial lavas in other volcanic terrains, 2) the distribution of primary hydrovolcanic clastic deposits at the TVC are confined to the cone, but coherent pillow lavas including distinctive vertically-oriented and distended pillows are widespread, 3) multiple lobes of massive sheet lavas record high initial magma discharge rates, 4) associated glaciogenic facies that underlie or onlap the TVC lavas indicate active subglacial meltwater drainage at the time of the eruption. Analyses of H2O/CO2 in pillow rim samples give broad constraints for emplacement pressures equivalent to 500-1400 m of overlying ice. No subaerial lava morphologies are found on the cone or in the proximal to distal lithofacies, and the ...