USING DIFFUSION CHRONOMETRY TO PREDICT VOLCANIC BEHAVIOR AT MOUNT HOOD, OR

Globally, more than 800 million people live in areas affected by volcanic hazards. Knowledge of the individual volcanoes and the timescale of volcanic eruptive processes can mitigate these hazards. In the case of Mt. Hood, Oregon, existing research indicates that injection of hotter, mafic magma into Mt. Hood’s shallower, silicic magma reservoir produces eruptions of mixed andesite magma. Diffusion chronometry on different crystals can constrain the time period expected for future eruptions between seismic, or other detection of increased activity, and eventual arrival of magma at the surface by measuring when the two magmas initially mix to when magma erupts. We have used studies of Mg diffusion in plagioclase and Fe-Mg diffusion in orthopyroxene (based on backscatter electron images) to estimate the time magma remained hot following mixing, with a result of 1-12 weeks. We have also applied diffusion chronometry based on zoned orthopyroxene crystals. Preliminary calculations form these produce longer timescales – up to ~ 1 year. Further studies will focus on the petrological processes that lead to mineral zoning in plagioclase and orthopyroxene, and on assessing our uncertainties.