Global Volcanism Program | Image GVP-03531
Hawaiian Volcano Observatory scientists conduct an electronic-distance measurement (EDM) survey on the rim of Kilauea caldera in 1988, with snow-capped Mauna Loa in the background. The procedure uses a laser beam, which is reflected back to the EDM instrument from a distant cluster of reflectors. A precise determination of the distance between the two points is made by a small computer in the EDM instrument. These measurements allow scientists to detect inflation or deflation of the volcano due to changes in the magmatic or hydrothermal systems.
Photo by J.D. Griggs, 1988 (U.S. Geological Survey).