Geothermal systems in volcanic arcs: Volcanic characteristics and surface manifestations as indicators of geothermal potential and favorability worldwide

This paper brings a global perspective to volcanic arc geothermal assessments by evaluating trends and correlations of volcanic characteristic and surface manifestation data from world power production sites in subduction zone volcanic settings. The focus of the work was to evaluate volcanic centers individually and as a group in these arcs by correlating various geologic characteristics with known potential to host electricity grade geothermal systems at the volcanic centers. A database was developed that describes key geologic factors expected to be indicative of productive geothermal systems in a global training set, which includes all 74 subduction zone volcanic centers world-wide with current or proven power production capability. Importantly, this data set only contains data from subduction zone volcanoes and contains no negative cases, limiting the populations of any statistical groups. Regardless, this is the most robust geothermal benchmark training set for magmatic-heated systems to date that has been made public. The work reported here is part of a larger project that included data collection, evaluation, correlations and weightings, fairway and favorability modeling and mapping, prediction of blind systems, and uncertainty analysis to estimate errors associated with model predictions. This first paper describes volcano characteristics, compositions and eruption ages and trends along with surface manifestation observations and temperatures as they relate to known power producing systems. Our findings show a strong correlation between the presence and size of active flank fumarole areas and installed power production. Additionally, the majority of volcanic characteristics, including long-held anecdotal correlations related to magmatic composition or size, have limited to no correlation with power production potential. Notable exceptions are correlations between greater power yield from geothermal systems associated with older (Pleistocene) caldera systems than systems hosted by Holocene calderas or non-caldera volcanic centers. Power-hosting volcanic centers that have erupted within the last 160 years supply 50% of the global installed geothermal power in subduction zones, and nearly all of these systems are generally mafic (basaltic or andesitic) in average composition. Volcanic centers erupting between 160 and 900 years ago are dominated by felsic volcanic systems, and provide 47% of the global power from volcanic arcs. Only 3% of geothermal power produced in subduction zones are hosted by volcanic center erupting more than 900 years ago. We anticipate that these results may be able to help guide future geothermal exploration efforts.