Devastated Area 1915/5/22 Effects of the Lassen Peak eruption of May 19-20, 1915. Taken on the morning of May 22, 1915, before the climactic eruption of that day, this photo shows a lava flow from the summit and the path of the destructive avalanche and debris flows of May 19-20. The large rock in the foreground, labeled "HOT ROCK" by the photographer, is a piece of a lava dome erupted in the crater of Lassen Peak between May 14 and 19 and disrupted by a volcanic explosion that reopened the crater and initiated the avalanche. Photo by B. F. Loomis, May 22, 1915, from the archives of Lassen Volcanic National Park.