April 6, 2026

According to the FAA, there are over 16 million flights a year in the U.S. and approximately 5,500 aircraft in the sky over the U.S. at peak times. Ash in the atmosphere from volcanic eruptions is a surprisingly common and very dangerous hazard that many people do not think about when making their travel plans.

Consisting of small, hard, sharp fragments of volcanic glass and minerals, volcanic ash is abrasive and melts at the operating temperature of jet engines. The abrasive ash sandblasts the outside of planes flying through it; meaning landing light covers and cockpit windows can cloud enough that lights become ineffective and pilot visibility is dangerously impacted. Inside the engines, turbine blades are damaged and ash melts and sticks to critical parts leading to potential engine failure. Navigation, communication and other onboard systems can be impacted by ash getting into sensitive electronics. When volcanic ash is above an airport, approach and departure becomes dangerous and when it settles on runways, braking is less effective and it becomes very slippery when wet.

Volcanic eruptions can occur very suddenly, injecting large amounts of dangerous ash at cruising altitudes within minutes. Then the volcanic ash cloud travels with the winds and can drift in different directions and at different heights, often ending up very far away from the original eruption. These clouds can linger in the atmosphere for days after an eruption. Pilots may have difficulty distinguishing them from regular clouds or smoke or dust layers by just looking at them and rely on warnings provided by Volcanic Ash Advisory Centers (VAAC) to keep them apprised of ash cloud location.

ARL is an expert on the transportation and dispersion of volcanic ash. This research improves dispersion forecasts used by the National Weather Service (NWS) and supports the wider volcanic ash community. In the 1980’s ARL developed a model that simulated the complex transport and dispersion of a 3-dimensional cloud of ash particles. This model was transferred to operations at the NWS. In 2005, ARL’s HYSPLIT model replaced the original model, this is used today by the NWS, two NOAA-operated VAACs and by the New Zealand and Australian VAACs.

Scientists at ARL continue research that improves volcanic ash dispersion forecasts and transfers new and updated HYSPLIT capabilities to the NWS for their volcanic ash dispersion forecasts. For instance, they work with the NOAA NESDIS-developed Volcanic Cloud Analysis Toolkit. This toolkit consists of AI-powered satellite applications which detect volcanic ash clouds and provide information on several properties, such as height. ARL inputs this information to the HYSPLIT model to improve forecasts and produce three dimensional pictures of ash clouds.

Dr. Alice Crawford, ARL’s HYSPLIT Group Lead, is a member of the Interagency Council for Advancing Meteorological Services Working Group for Volcanic Ash. She also supports the U.S. representative to the International Civil Aviation Organization (ICAO) Meteorological Operations Group.

As part of this work, Dr. Crawford participated in the ICAO International Airways Volcano Watch meeting on March 17-20. She presented the HYSPLIT team’s work on improvements for forecasting ash concentrations. She joined new working groups tasked to provide guidance materials for users on the new volcanic hazard services and improving ways to evaluate QVA information. Dr. Crawford was also part of discussions reviewing volcanic ash advisory services, including the future Quantitative Volcanic Ash information service (QVA), which will provide aviation users with detailed forecasts on ash concentrations and forecast areas where ash clouds may travel.