46.20 N, 122.18 W,
summit elevation 2549 m
Mount St Helens Volcano erupted on 1980 and was one of the best studied eruptions of the 20th century. The Mt St Helens eruption was the first on mainland US (excluding Alaska) since 1916. The eruption of Mount St Helens volcano on 18th May 1980 produced a 19 km (12 mile) high eruption cloud. Tremor, and two small earthquakes occurred at the volcano on 13th January 2008.
2011 Earthquake swarm
A swarm of earthquakes hit Mt St Helens volcano on 14th February 2011. The earthquakes were centered in an area near the Johnston Ridge Observatory, about 7 km north of the crater. The earthquakes had a focus at a depth of about 2-4 km. At least 12 small earthquakes were measured in the area since Monday. The initial earthquake was the largest with a magnitude of 4.3 and hit around 10:35 a.m. local time. The earthquakes are possibly caused by fault movement under the volcano as a result of magma removal during the 1980 eruption. Earthquake swarms occurred in the same area in January 2011 and August 1980. The USGS stated "at present there appears to be no signs of unrest in the volcanic system". The current volcano alert level for Mount St. Helen's remains at normal.
Lava dome growth paused in late January 2008.
2004-08, 1990-91, 1989-90, 1980-86, 1921?, 1903?, 1898?, 1857, 1854, 1853, 1850, 1849?, 1848, 1847, 1842-45, 1835, 1831
Eruption of Mt St Helens 1980
20th March, 1980
22nd April - 7th May
18th May 1980
Effects of the eruption.