Introduction » Mammoth Mountain: An Example of an Explosive Eruption

 

“Ash clouds are not an everyday issue and they do not provide frequent hazard. But if encountered, volcanic ash can spoil your entire day”

Donald D. Engen, VADM USN Retired
Introductory Remarks for the First International Symposium on Volcanic Ash and Aviation Safety, Seattle, Washington, July 1991

 

So, at this point you are probably asking yourself just why you need to know this? Whenever there’s a natural disaster, weather forecasters are among the first to be called upon for information and perhaps even advice on how to mitigate impacts. This is regardless of whether or not the natural disaster is weather-related. The forecaster on duty is seen not only as a Meteorologist, but also more generally as an Earth Scientist. You are often the only “expert” available for comment at all hours of the day and night. As the expert, you should:

  • understand the basics of volcanism and the impacts of eruptions so as to be able to speak intelligently on the subject
  • know where to turn for help in dealing with such inquiries or for additional information on an evolving volcanic eruption

“I was working the midnight shift on April 18, 2008 when a 5.4 magnitude earthquake struck south central Illinois. The telephone lines at the Weather Forecast Office in St. Louis were almost immediately inundated with calls. I was not, and am still not, an expert on earthquakes, but people were frightened and looking for information. The other forecaster on duty and I provided what information and reassurance we could, and this was greatly appreciated by all of the people with whom we spoke.”

Jon Carney
Meteorologist

 

While a volcano is not likely to erupt in your warning area, there is a very good chance that volcanic ash, or other processes and products related to eruptions, will affect people in your forecast area at some point in time. Consider the eruption of Mount Pinatubo. The more immediate impact from the eruption was to local area residents; however, in the longer term, the sulfate and aerosol clouds that circumnavigated the Earth produced one of the coolest and wettest summers in 1992. Many forecast offices were inundated with telephone calls from people asking why their crops had failed and why there were unusually brilliant sunsets.

As you play the following animation, consider:

  • Many of the Earth’s explosive volcanoes are located along the edges of tectonic plates where they are “crunching” together.
  • Mammoth Mountain and Cascade Range Volcanoes in California, Oregon, and Washington are located along the eastern periphery of the “Ring of Fire”. (To learn more about the Long Valley caldera visit the USGS link in the Reference section.)
  • What would be the impacts of volcanic ash in your forecast area?
  • How would you respond?

The left panel in this animation simulates a major eruption on Mammoth Mountain, California, with a significant emission of volcanic ash into the atmosphere. As a result, the Long Valley Observatory issues a Warning about the eruption which prompts the Volcanic Ash Advisory Center to run the HYSPLIT model (shown on the right). It provides a forecast for the transport and dispersion of volcanic ash. This, along with Urgent Pilot Reports and other information, is used by the Volcanic Ash Advisory Center (and Meteorological Watch Office) to produce volcanic ash advisories and SIGMETS.

With a ridge of high pressure over the Pacific Northwest and a low pressure center developing off the southern California coast, HYSPLIT shows an initial westward movement to the ash...at all levels...and heading toward Sacramento and San Francisco. This could cause significant ash accumulation and the US Geological Survey and local emergency managers warn the populace to stay indoors.

As the winds carry the ash offshore and to the south; ships and airplanes headed for facilities along the California coast are diverted to the north. Over time, the ash circles the low and begins to encroach southern California. In 24 to 36 hours, the dispersion model carries the low and mid-level ash across southern California and into the southwest United States. There appears to be a split flow in the upper levels with ash moving both westward and eastward toward Salt Lake City and the Rocky Mountains!

Air traffic destined to cities within the ash cloud area are diverted to airports farther north; or cancelled altogether. By 48 hours, the upper level winds have carried the ash across the Southern Plains and Gulf Coast states disrupting transportation. An eruption of greater magnitude and longer duration could have far reaching climatic impacts.