when was the last time mt lassen erupted
May 22, 1915
title: Lassen Volcanic National Park text: potential risk of other active volcanic areas in the Cascade Range. Further study of Cinder Cone estimated the last eruption occurred between 1630 and 1670. Recent tree-ring analysis has placed the date at 1666. The Lassen area was first protected by being designated as the Lassen Peak Forest Preserve. Lassen Peak and Cinder Cone were later declared as U.S. National Monuments in May 1907 by President Theodore Roosevelt. Starting in May 1914 and lasting until 1921, a series of minor to major eruptions occurred on Lassen. These events created a new crater, and released lava and a great deal of title: Geology of the Lassen volcanic area text: was created at the summit of the mountain. Less explosive activity continued through 1921. Some authorities, such as the Smithsonian, consider the eruption of Mount Lassen to have ended on June 29, 1917. 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 title: Lassen Volcanic National Park text: Approximately 350,000 years ago its cone collapsed into itself and formed a two-mile (3.2 km) wide caldera after it emptied its throat and partially did the same to its magma chamber in a series of eruptions. One of these eruptions occurred where Lassen Peak now stands, and consisted of fluid, black, glassy dacite, which formed a layer thick (outcroppings of which can be seen as columnar rock at Lassen's base). During glacial periods (ice ages) of the present Wisconsinan glaciation, glaciers have modified and helped to erode the older volcanoes in the park, including the remains of Tehama. Many of title: Lassen Peak text: The volcano arose from the destroyed northern flank of now-collapsed Brokeoff Volcano about 27,000 years ago, from a series of eruptions over the course of a few years. The mountain has been significantly eroded by glaciers over the last 25,000 years, and is now covered in talus deposits. On May 22, 1915, a powerful explosive eruption at Lassen Peak devastated nearby areas, and spread volcanic ash as far as to the east. This explosion was the most powerful in a series of eruptions from 1914 through 1917. Lassen Peak and Mount St. Helens were the only two volcanoes in the title: Geology of the Lassen volcanic area text: in the contiguous 48 U.S. states (after the 1980 eruption of Mount St. Helens in Washington). The most common volcanic activity over the last 50,000 years in the Lassen volcanic area consists of small to moderate-sized eruptions that produce basaltic lava flows and localized ash falls. These eruptions typically last a few months to a year, but may continue for several years. They can cover more than with lava flows, build cinder cones as high as , and blanket many square miles or square kilometers with ash a few inches (several cm) to about three feet (one meter) deep. Because