This is an image of Lassen Peak, in California, USA.
Click on image for full size
Image from: U.S. Geological Survey
Lassen Peak is an example of what is called a "volcanic dome".
Volcanism is thought to have begun at the center between about 600,000 and 350,000 years ago (the late Pleistocene and Holocene periods), and the eruption history continues with a lot of activity in the last 35,000 years.
The most recent eruptive activity occurred at Lassen Peak in 1914-1917. This eruptive episode
began on May 30, 1914, when a small phreatic eruption occurred at a new vent
near the summit of the peak. More than 150 explosions of various sizes
occurred during the following year. By mid-May 1915, the
eruption changed in character; lava appeared in the summit crater and
subsequently flowed about 100 m over the west and probably over the east
crater walls. Disruption of the sticky lava on the upper east side of Lassen
Peak on May 19 resulted in an avalanche of hot rock onto a snowfield. A
lahar was generated that reached more than 18 km down Lost Creek. Intermittent eruptions of variable intensity continued until about the middle of 1917.
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