Devastated Area 1915/7 Effects of the Lassen Peak eruption of May 22, 1915. Taken later in the summer of 1915 from the same location as the photo taken on the morning of May 22, this photo shows the additional area devastated by the pyroclastic flow and fluid debris flows of May 22. The toe of the summit lava flow has been swept away. Trees that had remained standing on the morning of May 22 were blown down or snapped off above the ground, their fallen trunks pointing away from the summit of Lassen Peak. The effects of the May 22 eruption were diverted by topography and did not reach the "HOT ROCK". Photo by B. F. Loomis, July, 1915, from the archives of Lassen Volcanic National Park.