TIMESCALES OF MAGMA STORAGE AND ERUPTION INITIATION OF THE MOST RECENT LAVA FLOW IN THE MOUNT BAKER (KOMA KULSHAN) VOLCANIC FIELD, WA

Mount Baker, ranked as a very-high threat volcano in the United States, is in a well-populated area in northern WA, putting many at risk in the event of a future eruption. Previous work on Mount Baker has focused on understanding the magmatic architecture beneath the volcano and has identified multiple magmatic components that contributed to different eruptions throughout its history. The youngest lava flow in the Mount Baker Volcanic Field is the 9.8 ka Sulphur Creek lava flow. The last study conducted on this flow was done by Garvey (2022) who determined the most recent magma mush configuration that was tapped for this eruption. This included finding four co-crystallizing mineral assemblages and their respective equilibrium liquids representing four distinct magma mushes stored at a variety of depths beneath Mount Baker. However, it is still unknown how long these mushes were stored in an eruptible state before the eruption and how quickly the final ascent of magma to the surface was after the eruption initiation mechanism. Using EPMA and LA-ICP-MS, chemical gradients across individual crystals were collected for thermometry and diffusion chronometry. Temperatures were determined using ThermoBar (Wieser et al., 2022) via plagioclase-liquid and clinopyroxene-liquid thermometers. Core to interior zones of Mg and Sr in plagioclase were analyzed at 750 °C for residence timescales and are on the order of centuries to one millennium. The interior zones to the rims of Fe-Mg interdiffusion in clinopyroxene were analyzed using the temperatures calculated with ThermoBar to produce eruption initiation timescales. Preliminary results for individual clinopyroxene crystals suggest timescales of an eruption initiation period on the order of a few years. This work provides insight into timescales associated with an active magma system in the Cascades that has no diffusion studies to date and assists in planning for hazard and risk mitigation in the case of a future eruption at Mount Baker.