Geochemists from the Lawrence Berkeley National Laboratory and Arizona State University have discovered a new tool for identifying potential geothermal energy resources. The discovery came from comparing helium isotopes in samples gathered from wells, springs, and vents across the northern Basin and Range of western North America. High helium ratios are common in volcanic regions. When the investigators found high ratios in places far from volcanism, they knew that hot fluids must be permeating Earth's inner layers by other means. The samples collected on the surface gave the researchers a window into the structure of the rocks far below, with no need to drill.
"A good geothermal energy source has three basic requirements: a high thermal gradient—which means accessible hot rock—plus a rechargeable reservoir fluid, usually water, and finally, deep permeable pathways for the fluid to circulate through the hot rock," says Mack Kennedy. "We believe we have found a way to map and quantify zones of permeability deep in the lower crust that result not from volcanic activity but from tectonic activity, the movement of pieces of the Earth's crust."
Geothermal is considered by many to be the best renewable energy source besides solar. Accessible geothermal energy in the United States, excluding Alaska and Hawaii, is estimated at 90 quadrillion kilowatt-hours, 3,000 times more than the country's total annual energy consumption. Determining helium ratios from surface measurements is a practical way to locate promising sources.
Julia Whitty is Mother Jones' environmental correspondent. You can read from her new book, The Fragile Edge, and other writings, here.