203 Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder

We encourage papers that challenge and give insights into the interplay between timescales, methodologies, and processes to build a cohesive understanding of the lifespan, evolution, storage, and eruption of magma, from plutonic to volcanic systems.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

Timescales of chilling lava with arctic air: Thick glassy rinds on the Lost Jim flow field, Alaska.

Paper number: 203-7
Program: Technical Sessions
Time: 3:15 PM – 3:30 PM

Authors

Abstract

Compared to other processes during magma generation, storage, and eruption, the cooling of the outermost surface of a lava flow is often considered to be effectively instantaneous. However, even small variations in cooling rates between different local environments can change the glassiness of the outer rind. The basaltic Lost Jim lava flow field is 34 km long and located in the center of the Seward Peninsula, Alaska. Given the flow size (3-4 km3) and an effusion rate similar to Holuhraun in 2014-15, a substantial amount of lava would have been emplaced during the arctic winter months (roughly October-April). New 36Cl cosmogenic exposure ages were found to be 7.83 ± 0.77 ka and thus, the climate at the time of eruption was cold and capable of chilling lava quickly. We compare the glassiness of the outer surface of the Lost Jim flow field with the surfaces of lava flows emplaced in the temperate desert (Idaho, Oregon, and California) to examine if surface water and arctic temperatures allow for faster cooling rates and increased glass-to-crystal ratios of the outer surface of the lava flow. Glassiness was measured as the modal % of the outer 50 microns of the sample as viewed with an SEM. The thickness of the visibly glassy rim was also measured on standard petrographic thin sections. Analyses of the glass abundance of 23 samples from emplacement environments, including vent-proximal, wet margin, dry margin, and mid-flow far from the final edges of the flow, had an average of 74% glass and 6.4 mm thick rinds (where material becomes opaque instead of transparent). This is compared to 31 desert lava samples from 5 different flows, which had an average of 60% glass in rims that are 2.9 mm thick. We interpret increased glass content as a result of faster cooling in an arctic environment. Samples of the Lost Jim flow collected near modern lake edges were not significantly glassier than dry margin samples, suggesting that either the overall temperature of the region had a bigger influence in cooling the Lost Jim flow than surface water – lava interactions, or that the water contacts were not in the same locations during cooling.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412503

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