On May 30, 1914, despite an apparent lack of precursor earthquakes, Lassen became volcanically active again after 27,000 years of dormancy, when it produced a steam explosion that carved out a small crater with a fairly deep lake on the volcano's summit. The crater grew as it was carved by more than 180 similar phreatic explosions over the span of more than 11 months, reaching a length of . On May 14, 1915, Lassen Peak erupted lava blocks, which extended as far as Manton, west of the mountain. By the next day, the volcano had produced a dacitic lava dome, between 63 and 68 percent silica, which occupied its summit crater. On May 19, a large eruption destroyed this dome, and a new crater formed at the summit. No lava erupted, but parts of the dome fell on the upper flanks of the mountain, which were covered in more than of snow. The lava mixed with snow and rock to form a lahar (volcanically induced mudslide, landslide, and debris flow), in width, which coursed down the side of the volcano, traveling and reaching Hat Creek. After being deflected to the northwest at Emigrant Pass, the lahar extended an additional down Lost Creek. On May 20, the lower Hat Creek valley flooded with muddy water, which damaged ranch houses in the Old Station area and caused minor injuries among a few people, all of whom escaped. Removing homes from their foundation, the lahar also uprooted trees more than tall. The flood continued for another , killing fish in the Pit River. Simultaneously, dacite lava with lower viscosity than dacite from the previous eruption filled the summit crater, overflowing and extending in two streams for down the mountain's western and northeastern sides.