National Weather Service United States Department of Commerce

There are over 150 volcanoes in the United States that scientists consider to be active. Most are in Alaska with many others in Hawaii and throughout the West. Volcanic eruptions are a geologic phenomenon and not weather, but wind can transport volcanic ash from explosive eruptions thousands of miles from a volcano. National Oceanic and Atmospheric Administration (NOAA) meteorologists monitor the status of active volcanoes, track volcanic ash in the atmosphere during eruptions, and issue advisories and warnings for airborne ash and ashfall.

Major Threat to Aviation

Airborne volcanic ash is a major hazard of all explosive eruptions. Aircraft encounters with ash clouds can diminish visibility, damage flight control systems, and cause jet engines to fail. Air traffic controllers and pilots must be quickly notified of volcanic eruptions to avoid volcanic ash clouds. NOAA forecasters at the Washington DC and Anchorage Volcanic Ash Advisory Centers (VAAC) and those in Center Weather Service Units (CWSU) play a key role in this effort.

Impacts of Ashfall on Health, Business and Infrastructure

Impacts from ashfall depend on distance from the volcano, physical properties of the ash, the amount of ashfall, and the readiness of a community to respond. Communities near volcanoes are at the greatest risk for ashfall although it can be a problem hundreds of miles from a volcano after a major eruption. Volcanic ash can create eye and upper airway irritation. Ashfall can cause minor to major damage to vehicles and buildings, contaminate water supplies, disrupt sewage and electrical systems, and damage or kill vegetation. After ashfall, affected airports must be closed until ash is removed because of its hazard to jet engines. Roads near the volcano may be impassable until cleared. NWS Weather Forecast Offices (WFO) collaborate with VAACs and other state and federal agencies to issue ashfall advisories and warnings.

Actions to Take Before, During and After an Event

Before an Eruption: Ensure that safety glasses and dust masks are in the emergency supply kits at your home, at work, and in your car. You should have at least one set per person.

During an Eruption:

  • Stay calm.
  • Wear safety glasses and and dust masks. Inhaling ash can be very harmful to your health.
  • Stay indoors.
  • If outside, seek shelter as quickly as possible.
  • If you must drive, use low speeds and ensure you have plenty of windshield washer fluid.
  • Place damp towels at door thresholds and other draft sources.

After an Eruption:

  • Stay tuned to your trusted local news source for the latest updates.
  • Follow instructions from local officials.
  • Continue to protect your eyes, mouth, and nose until ash has settled and been cleaned up.

Volcanic Ash and Ashfall Resources

volcanic ash
Ash from an eruption of Alaska's Pavlof Volcano. Image Courtesy of AVO/USGS.  Photo by M. L. Coombs.