Lassen Volcano - John Seach


California, USA

40.49 N, 121.50 W
summit elevation 3187 m

Lassen volcano is located in northern California, at the southern end of the Cascade Range.

1992 Earthquakes
On 28th June 1992 a magnitude 7.5 earthquake occurred 800 km SSE of the volcano. A magnitude 2.8 earthquake was recorded at Lassen Peak 10 minutes after the arrival of the S wave from the tectonic earthquake. A total of 22 earthquakes were recorded at Lassen volcano in the first 24 hours.

1914-17 Eruption
The 1914-17 eruptions of Lassen peak was the first of only two volcanoes to erupt in the continental USA in the 20th century. Activity began on 30th May, 1914 with a phreatic explosion at the summit of Lassen Peak. An eruption on 22nd May 1915 devastated an area of 7 sq km on the NE of the volcano. Lahars descended Lost Creek, with minor lahars flowing down valleys on the west, northwest and north flanks of the volcano. The lahar was triggered by melting of snow by pyroclastic flows.

On 12th June 1914, a climbing group of five people were caught half a mile from the crater during an eruption. Milton Ayres, a San Francisco movie camer operator described the event.

"We had no warning. The roar and the uprush of the black mass above were simultaneous. The rocks began to fall on the mountain side; the gases did not come our way much, as the wind drove them to the east, but we got some strong whiffs of sulphur smoke. For the same reason little ash fell where we were. Later we went on to the summit, reaching it at 6 P. M., two hours after the eruption began. We found the whole mountain top strewn with great boulders and heavy ash. No one could possibly have lived at the top while the outburst was on. We climbed up to the shelter house, where we had expected to spend the night, and found it in ruins. Boulders had crashed down through it and splintered the building to kindling wood."

Lassen Volcano Eruptions

1914-17, 1650?