Explosions recurred at irregular intervals on Lassen Peak for most of 1914. Later, on May 19, 1915, a mass of lava rose in the summit crater and spilled down the western side of the volcano. Extensive lahars (mudflows) were created on the northeastern side as snowbanks were melted. The resulting debris swept down the slope. Divided by Raker Peak, part of this mudflow raced down Lost Creek; the remaining flow passed over the rise east of the park road and rushed down Hat Creek. A wide barren swath was torn through the forest.