Since then , the volcano has been dormant , although some steam still rises from small vents in its summit and on its flanks . Pumice ejected during the 1915 eruption of Lassen Peak is conspicuously banded with light streaks of dacite and dark andesite , which appears to represent two distinct magmas imperfectly mixed during the eruption . The 1915 eruption of Lassen Peak was the second most recent volcanic outburst in the contiguous 48 U.S. states ( after the 1980 eruption of Mount St. Helens in Washington )
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Geology of the Lassen volcanic area