NEW MONITORING TECHNIQUES FOR HYDROTHERMAL SYSTEMS OF POAS AND TURRIALBA VOLCANOES, COSTA RICA

New instrumentation installed measures temperatures of the ultra acidic crater lake and fumaroles at Poás and Turrialba volcanoes of the Central Cordillera, Costa Rica. The active crater of Poás hosts a highly dynamic lake, Laguna Caliente, with low pH (-0.87 - 1.75) and temperatures that have ranged from 22 - 94°C in the last three decades. A recent compilation of over 20 years of gravity data indicates that Poás is currently in an episode of magma intrusion, which based on previous events, likely precedes temperature and chemical changes in the lake on order of years (Rymer et al., 2009). Degassing and seismic activity at Volcán Turrialba have increased since 2005, prompting increased monitoring efforts. Fumarole temperatures and gas compositions reflect further increased activity since 2007. Gas fumes dispersed by trade winds toward the NW, W, and SW flanks of Turrialba volcano are the cause of significant vegetation kill zones. Summit surface fractures are oriented parallel to the major fault system, so fumarole temperatures are monitored in fractures in an attempt to correlate fracture activity with magmatic pulses. Previously, water and fumarole temperatures and compositions at Poás and Turrialba volcanoes were measured approximately once a month. This presentation highlights new crater lake and fumarole temperature data that are now recorded every 15 minutes at each volcano. Using methods developed at Lassen Volcanic Center in the Cascades arc, temperature probes and data loggers were installed at Poás and Turrialba in June 2009. Initial data show that these methods are capable of providing high quality, meaningful data. Crater lake temperatures recorded at Poás volcano increased consistently from 52-53 °C, with several deviations attributed to surface water inflows during rainstorms. Turrialba Cráter Oeste fumarole temperatures average 83 °C, but drop periodically (several times daily) as much as 8 °C. Temperatures continue to be recorded and are downloaded bi-monthly at both volcanoes in an attempt to record small scale variations that can be correlated to other monitoring data sets (e.g. GPS, lake and fumarole geochemical compositional data, volcanic seismicity, etc.) for thorough monitoring of the hydrothermal and magmatic systems of Poás and Turrialba volcanoes.