Lassen Peak, Plug dome volcano in Shasta County, United States.
Lassen Peak is a plug dome volcano made of dacite rock in Shasta County in northern California, rising to 3,189 meters (10,463 feet) above sea level. The steep slopes display the characteristic gray color of volcanic rock, while the summit area often retains snow patches even during summer months.
The eruption began in May 1914 and produced lahars, pyroclastic flows, and ash ejections over three years that destroyed surrounding forests. This volcanic activity led to the establishment of Lassen Volcanic National Park in 1916 to protect the area and its geological features.
The name honors Peter Lassen, a Danish blacksmith who guided settlers through the region during the 19th century. Today hikers encounter interpretive signs along trails explaining the geological formation and the mountain's importance to indigenous peoples.
The ascent starts from a parking area near the main road and follows a well-marked trail that switchbacks to the summit. Hikers should start early to avoid afternoon thunderstorms and bring warm clothing, as temperatures drop noticeably with elevation gain.
Fumaroles near the summit continuously release sulfur vapor that becomes visible as white clouds during cold weather. This steam venting shows that magma chambers still exist beneath the mountain, heating the rock above.
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