The occurrence, size and geometry of geothermal resources in volcanic terrains

Volcanic terrains in general, and arc volcanic belts in particular, have been prime geothermal exploration targets as far back as the first geothermal power generation at Larderello, Italy, in 1904. The popularity of this terrain for geothermal exploration and development is based on the concept of young shallow magma bodies providing an abundance of shallow crustal heat and also on the presence of hot springs and fumaroles observed within these terrains. The success in developing these geothermal resources ranges from spectacular (e.g. Japan, Philippines, Indonesia, New Zealand, Italy, Iceland) to disappointing (e.g. Cascade Range of northwestern North America). The types, shapes and geometries of geothermal resources in volcanic terrain range in size from large broad three-dimensional fractured stockwork systems to narrow geothermal cell conduits. Effective and economic exploration and development of these resources is greatly improved by understanding the varying sizes and geometries of these resources and matching the exploration strategy design specifically for each exploration target rather than applying a single exploration formula and data interpretation model to all settings. Information from the mining industry provides valuable insight into the range in geometry and size of these resources. This body of knowledge should be used by the geothermal community: (1) for more effectively designing exploration programs specific; (2) to each prospect to interpret the body of exploration data in terms of site-specific geology and tectonics; (3) to integrate basic risk management best practices into exploration and development programs.