Millions of people ride jetliners every year, but few are aware of the hazards of volcanic eruption clouds. Over the last 15 years (as of 1995) there has been about 25 incidents in which turbine aircraft have flown through eruption clouds resulting in jet flame-out. In each case damage to aircraft has cost tens of millions of dollars, but no lives have yet been lost. The increase in engine failures from ash ingestion since 1982 is because jet engines run at higher temperatures than older aircraft. At cruising altitudes, 150 tons of air per minute passes through each of the four engines on a Boeing 747. If there is ash in the air, tons of it is filtered through the engines. This can occur even if the ash clouds are barely visible to a pilot's eye and are undetected by normal radar signals. Busy airline routes, such as through Alaska, need constant monitoring.
There are several places that monitor the pathways of ash clouds such as the Darwin Volcanic Ash Advisory Centre in Australia.
Fine-grained volcanic ash easily melts. Flame-out of jet engines occurs because the melted silicate ash forms a thin coat of glass on metal surfaces of the turbine vanes. Large volumes of ash sucked into the engines can also cause corrosion of metal parts and surface coatings in the hot sections of the jet engines. It can contaminate plastic insulation and neoprene hosing in air distribution systems and corrode electrical contacts. Pitting, crazing, etching and embrittlement of windows can be caused by acid aerosols. The dielectric properties of some coatings that cover printed circuit cards may change due to the presence of the volcanic gases. Volcanic dust can damage landing lights, clog systems that help calculate airspeed and altitude for the pilots, and damage sensors that deliver electronic data to automated systems used to fly modern aircraft.
Though eruptions can be brief and in remote areas, potentially dangerous ash clouds can move rapidly from their source into populated areas and air corridors without notice until ash the falls or aircraft is damaged. In northern Chile on September 16, 1986, Lascar volcano produced a 15-kilometer-high eruption column. The ash moved rapidly downwind as a 2 kilometer-thick eruption plume between elevations of 10 to 14 kilometers in the atmosphere. The eruption plume passed over the city of Salta, Argentina, 285 kilometers from Lascar less than 2 hours after the eruption. Ash fell on the Salta airport, but there were no aircraft incidents. About 3.5 hours after the eruption the plume had travelled 400 kilometers over an area of 100,000 square kilometers.
Prevailing winds over Klyuchevskoy volcano are from the west and northwest, and therefore send airborne ash across the numerous North Pacific air routes. The volcano erupted on September 30, 1994 and disrupted air traffic across the North Pacific for 60 hours. The ash plume rose 18,600 meters and strong 240 kmp winds carried the ash southeast as far as 1030 kilometers in the heavily traveled North Pacific air routes at flight levels of 9610 meters to 11,780 meters. These routes are used by 70 flights a day carrying about 10,000 passengers.
For more information contact Thomas P. Miller, Alaska Volcano Observatory, U.S. Geological Survey, 4200 University Drive, Anchorage, Alaska 99508.