You're actually confusing three people caught in the 1980 eruption of Mount St. Helens:
David Johnston: The volcanologist stationed at the Coldwater II observation post (now Johnston Ridge). He was able to make one quick radio call to the USGS before he was killed by the lateral blast and buried by the landslide. His body and equipment were never found.
Reid Blackburn: A photojournalist covering the buildup to the eruption. He was killed when the pyroclastic flow engulfed the area in which he was camped. His car, body, and camera were recovered, but the film was damaged by the intense heat and was not salvageable.
Gary Rosenquist: An amateur photographer camped near St. Helens with a few others. One of his party mentioned that the side of the mountain was becoming "fuzzy," and Rosenquist pointed his camera and held down the shutter release. He survived because the pyroclastic flow was diverted by a series of ridges away from his campsite.