Hawaiian Volcanos Observatory Scientists Say Geothermal Drilling Won't Cause Sinking

Kilauea Volcanic Rift Zones subside whether or not they host geothermal developments

Recently, Hawaiian Volcano Observatory scientist’s have been asked if Hawaii Island’s geothermal development causes subsidence of the ground surface, as has been observed at U.S. mainland geothermal areas, such as those in California– Coso, Geysers, the Imperial Valley, and Casa Diablo in the Mammoth Lakes area.

The largest of these mainland developments is heated by magma reservoirs that supplied eruptions through non-volcanic rock layers. The magma, thousands of years old, still heats groundwater within California’s sedimentary basins, where, fluid withdrawal during geothermal energy production can reduce pressure within the subsurface rock formations. When this happens, the ground surface subsides.

The highest subsidence rates are measured at the Geysers Geothermal Field within the Clear Lake Volcanic Field in northern California. The 78 square kilometer (30 sq mi) developed area produces 1,500 megawatts (MW) of electricity from a vapor-dominated reservoir within fractured sandstone that is capped by a zone of rock filled with geothermal minerals at the top and heated by magma below.

The Clear Lake volcanic field is one of several in California and Nevada that are monitored by HVO’s sister California Volcano Observatory (CalVO; http://volcanoes.usgs.gov/observatories/calvo/). CalVO also monitors the Long Valley caldera, in which the Casa Diablo geothermal development (40 MW) is located; the Salton Buttes volcano, which includes the Imperial Valley geothermal field (>300 MW); and the Coso Volcanic Field, where a 270 MW geothermal development is located.

As volcanic activity waxes and wanes, each of these areas exhibits its own deformation and seismicity. For example, the Long Valley caldera has experienced several episodes of heightened unrest, including earthquake swarms, ground uplift, and volcanic gas emissions during the past several decades. Thus, CalVO watches this area closely. The subsidence related to geothermal development must be documented carefully to separate the effects of volcanic activity from those due to drilling and energy production.