In addition to his work, Johnston himself has become part of the history of volcanic eruptions. With Harry Glicken, he is one of two volcanologists from the United States to die in a volcanic eruption. Glicken was being mentored by Johnston, who relieved Glicken of his watch at the Coldwater II observation post 13 hours before Mount St. Helens erupted. Glicken died in 1991, eleven years later, when a pyroclastic flow overran him and several others at Mount Unzen in Japan.