Volcano Information

    Lassen Volcanic Center
    Volcanic Alert Level: NORMAL Aviation Color Code: GREEN

    • Current Update, last updated Mar 19, 2009 07:29 PDT:
      Information Statement for the recent March 17-19, 2009, Lassen Peak swarm activity

      A series of small earthquake swarms have occurred beneath the south flank of Lassen Peak in Lassen Volcanic National Park over the last three days. This activity began at 3:00 AM (PDT) on March 17 and persisted through 8:16 AM on the 19th. Episodic swarm activity on the 17th through 4:10 AM on the18th included some 48 earthquakes large enough to be located, the three largest of which had magnitudes of M=2.1, 2.0, and 2.2. Activity resumed at 6:57 AM on the 19th producing 26 earthquakes by 8:19 AM, the largest of which was a M=1.9. These earthquakes are centered at a depth of roughly 5 km beneath the surface and, in map view, form an elongated pattern extending from the vicinity of Eagle Peak on southwest flank of Lassen Peak to the vicinity of Diamond Peak 3 km further to the south-southwest.

      Earthquake swarms are not unusual in this area. This most recent activity was preceded by a swarm of 12 earthquakes on February 13-14 that included a M=1.8 event. Earlier activity in this same area over the last five years includes swarms on February 15-16, 2005 (14 events including a M=2.3 earthquake), February 21 2006 (13 events with a M=2.2 earthquake), January 18-19, 2007 (29 events with a M=1.9 earthquake), and September 7-8, 2008 (41 events with a M=2.3 earthquake). This swarm activity over the past 3 days appears to be within the norm of earthquake activity detected in the Lassen area since the modern seismic network was installed in 1980. The USGS will continue to monitor the situation closely.
    • Volcanic History Overview: The Lassen volcanic center consists of the andesitic Brokeoff stratovolcano SW of Lassen Peak, a dacitic lava dome field, and peripheral small andesitic shield volcanoes and large lava flows, primarily on the Central Plateau NE of Lassen Peak. A series of eruptions from Lassen Peak from 1914 to 1917 marks the most recent eruptive activity in the southern Cascade Range. Activity spanning 600,000 years began with construction of Brokeoff stratovolcano. Beginning 400,000 years ago activity shifted to the north flank of Brokeoff, where episodic, more silicic eruptions produced a field of a dozen dacitic lava domes including Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak. At least 12 eruptive episodes took place during the past 100,000 years, with Lassen Peak being constructed about 28,000 years ago. The Chaos Crags dome complex was constructed about 1100-1000 years ago north of Lassen Peak. The Cinder Cone complex NE of Lassen Peak was erupted in a single episode several hundred years before present and is considered part of the Lassen volcanic center (Clynne et al., 2000). The 1914-1917 eruptions of Lassen Peak began with phreatic eruptions and included emplacement of a small summit lava dome, subplinian explosions, mudflows, and pyroclastic flows.
    • Location: Western US, CA

      Latitude: 40.492
      Longitude: -121.508
      Elevation: 3187 m

      Recent Eruption: 1914 to 1917 eruptions
    • Hazard Assessments: Miller, C. Dan, 1989, Potential Hazards from Future Volcanic Eruptions in California, USGS Bulletin 1847, 17 p. ill., maps.
    • Link to monitoring data: