HYDROTHERMAL MONITORING OF RESTLESS VOLCANOES IN THE US

The United States has ~170 young volcanoes capable of erupting. From 1980-2015, 44 different U.S. volcanoes produced 115 eruptions and 51 episodes of notable volcanic unrest. Earthquake swarms, sequences of sustained seismic activity, represent the most broadly used indicator of volcanic unrest, yet the vast majority of earthquake swarms do not culminate in an eruption. Hydrothermal systems, more difficult to monitor remotely, are also sensitive to underlying unrest and can provide a critical complement to the seismic and geodetic data streams that are the backbone of most volcano-monitoring efforts. A November 2014 earthquake swarm at Lassen, California, which included the largest earthquake in the area in more than 60 years,was accompanied by a rarely observed outburst of hydrothermal fluids. Long-term, multiparametric monitoring at Lassen and other well-instrumented volcanoes enhances interpretation of unrest and can provide a basis for detailed physical modeling.