Legend
Volcano Map Legend
The sizes of symbols scale with earthquake magnitude, and their color with either the age of the earthquake or its depth, as shown in the legend below, and selected in the Control Panel. Clicking on an earthquake symbol shows its basic information and a link to a page with more details about the individual earthquake.
Control Panel
Volcano Map Panel
Using the tools in this panel you can control the earthquakes shown on the map. The minimum magnitude to plot is selected by the slider. The "Time" and "Depth" determines whether earthquake age or depth are used to color the symbol.
Cross Section
Cross Section
To view events in profile, click "Define X-Section", select two points on the map, drag the box to include events you would like to plot and then click "Plot X-Section." The perspective is looking through the cross section line and into the box.Last 20 Events
| Mag | Time (Local) | Depth (Km) |
|---|
Mount St. Helens is the most historically active volcano in the Cascade range, having produced four major explosive eruptions since 1479, and dozens more smaller eruptions, including pyroclastic flows, lava flows and domes, and lahars. It is located approximately 80 km NE of Portland, OR.
Mount St. Helens is best known for its large explosive eruption, summit collapse and directed blast of May 18, 1980, which was the most expensive and deadly volcanic event in United States history. The volcano continued erupting during 1981-1986, producing a lava dome within the 1980 crater. Mount St. Helens last erupted in 2004-2008, when it produced a series of spectacular lava spines with a cumulative volume of almost 100 million cubic meters. Tremor and millions of small earthquakes accompanied both of the recent eruptions.
More information about Mount St. Helens
More information about the 1980-1986 eruption
More information about the 2004-2008 eruption
Background Seismicity
The Cascades Volcano Observatory and the PNSN cooperatively operate 21 seismometers on or near Mount St. Helens. On average, we locate 4 to 14 earthquakes within 10 km of the volcano each week. Mount St. Helens and the nearby St. Helens Seismic Zone occasionally produce swarms of many small earthquakes, but these are not usually directly associated with magmatic activity. An additional challenge on Mount St. Helens is that small rockfalls commonly occur on the steep crater rim.