Global Volcanism Program | Image GVP-02750
Two U.S. Geological Survey volcanologists (left center) take gas samples from a fumarole, one of many across the wall of Sherman Crater in 1981. Increased emissions had begun from Sherman Crater in 1975. The crater walls consist of brightly colored areas of hydrothermally altered rocks.
Photo by Bill Chadwick, 1981 (U.S. Geological Survey).