Potentially Active Volcanoes of the West

The western United States is home to 20 potentially active volcanoes.  Just over half of these have shown activity in the past 2000 years. 

The volcanoes of the western United States, especially those in the Cascades, are the result of subduction of oceanic plates beneath the edge of the North American Plate.  The oceanic plates are made at mid-ocean ridges and are denser than the North American Plate.  The North American Plate is made of continental crust and lithospheric mantle.  Water from the oceanic plate helps to melt the hot asthenospheric mantle beneath the North American Plate.  Magma rises through the plate to supply volcanoes.

Plate tectonics continues to drive our volcanoes.  Eruptions of active volcanoes are imminent but very widespread.

In the bookstore: Volcanoes 

On the web: USGS map

Image above: Mount Shasta 1984 (USGS)

Mount St. Helens Current Status: “Watch”

Under the current U.S. Geological Survey Alert Level Terminology, Mount St. Helens volcano status is at “watch” level.  There are four levels in the system: Normal, Advisory, Watch, and Warning.

Here is the most current update from the USGS:

U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismic Network, Seattle, Washington

Wednesday, February 6, 2008 08:46 PST (Wednesday, February 6, 2008 16:46 UTC)

MOUNT ST. HELENS UPDATE

Current Volcanic- Alert Level WATCH; Aviation Color Code ORANGE: Growth of the new lava dome inside the crater of Mount St. Helens continues, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. During such eruptions, changes in the level of activity can occur over days to months. The eruption could intensify suddenly or with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.

Potential ash hazards: Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that any ash clouds rising above the crater rim today would drift to the east and southeast.

Potential ash hazards to aviation: Under current eruptive conditions, small, short-lived explosions may produce ash clouds that exceed 30,000 feet in altitude. Ash from such events can travel 100 miles or more downwind.

Recent observations: Mount St. Helens remains shrouded in clouds this morning. Generally stormy weather continues in the region, and more snowfall is expected today and tonight. Seismicity at the volcano remains very low. While most instrument sites continue to function, several have experienced transmission problems over the last few days, presumably due to snow/ice accumulation.

The U.S. Geological Survey and the University of Washington continue to monitor the situation closely and will issue additional updates and changes in alert level as warranted.

In the bookstore: Mount St. Helens (books)

On the web: USGS Cascades Volcano Observatory