Emplacement of volcaniclastic mass flows during the 2023 eruption of Shishaldin Volcano, Alaska

Eruption-caused volcaniclastic mass flows were a significant feature of the four-month-long 2023 eruption of Shishaldin Volcano in Alaska. The volcano supports a nearly continuous cover of glacier ice and snow on the flanks of its upper edifice, and the emplacement of pyroclastic density currents over this snow and ice cover led to the generation of meltwater and lahars. Pyroclastic density currents that formed during the eruption were long and narrow in map view and did not develop marginal levees. Although the upper part of the Shishaldin Volcano cone is very steep (> 30 degrees), pyroclastic density currents typically travelled less than 2 km. These limited-runout flows resulted from low-level column collapse on all flanks of the volcano, but primarily on the north flank. A few episodes of lava fountaining in the summit crater resulted in the formation of small, unstable mounds of spatter and agglutinate. The mounds occasionally collapsed, forming hot, granular, incandescent flows. Pyroclastic density currents formed by all mechanisms interacted with snow and ice on the edifice to produce lahars. The pyroclastic density currents and lahars that formed throughout the 2023 eruption were similar to the eruptive products generated by previous historical eruptions of Shishaldin Volcano.