July 22, 2004
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Avoiding Airborne Volcanic Ash Anywhere in the World
Aircraft and volcanic ash and gases do not mix well.
Jet aircraft are designed to fly through clean air, but volcanic eruptions can dirty clean air with millions of tons of acid gases and sharp, tiny rock fragments known as volcanic ash.
Explosive eruptions create billowing columns of pulverized ash and gas that rise from a few hundred to many tens of thousands of feet above Earth's surface. Depending on the prevailing wind, the tiny rock fragments may form a dense cloud of ash extending more than 3,200 km (2,000 miles) from an erupting volcano.
Ash clouds can move away from a volcano in different directions at varying heights above the ground. Unfortunately, the ash clouds usually look like typical weather clouds during daylight, and they cannot be seen at night.
It doesn't take long, however, for pilots and passengers to recognize the signs that their aircraft has flown into an ash cloud -- the unmistakable smell of sulfur in the aircraft, sudden darkness outside, and static discharges around the front windscreen or on wingtips.
Modern jets transporting hundreds of people and tons of cargo across the globe have flown into these clouds of volcanic ash at least 100 times in the past 25 years. Such encounters have resulted in hundreds of millions of dollars of aircraft damage and, in seven cases, caused in-flight engine failures.
One of the most infamous encounters occurred downwind of Redoubt Volcano, located 177 km (110 miles) southwest of Anchorage, Alaska. A 747 jumbo jet approaching the Anchorage International Airport on December 15, 1989, flew into Redoubt's ash cloud and lost power in all four engines.
After gliding powerless for more than four frightening minutes and falling nearly 3.5 km (12,000 feet) to within a few thousand meters (yards) of the ground, disaster was narrowly averted when the pilots were able to restart the engines and land safely despite the severely "ash blasted" front windows.
This near-disaster immediately spawned a serious effort in the United States and abroad to keep aircraft away from volcanic ash clouds. Scientists, pilots, air traffic managers, and representatives of the airline industry from around the world worked together to deal with this newly recognized hazard to aircraft during an international conference, Volcanic Ash and Aviation Safety, held in Seattle, Washington, in 1991.
Experts from many disciplines considered the conference a great success because of the many subsequent procedures, agreements, and education efforts developed to get critical information about volcanic eruptions and ash clouds in the hands of pilots quickly at all times throughout the world.
Now, 13 years later, a second international ash and aircraft conference-Avoiding Airborne Volcanic Ash Anywhere in the World-was held last month in Alexandria, Virginia. The international scientific, aviation, and regulatory groups currently involved in mitigating the ash threat to aircraft met to discuss what remains to be done to ensure that pilots avoid volcanic ash.
The conference succeeded in promoting the exchange of scientific and operational information on ways to reduce the risk of ash to aircraft. The basic strategy developed in the past 13 years to keep aircraft away from ash clouds is working, but there are things that can, and should, be strengthened.
For example, volcanologists should continue to increase the number of monitoring instruments on all active and potentially explosive volcanoes so that they can better detect signs of activity before an eruption begins and accurately report the status of an ongoing explosive eruption to the aviation community, as well as to communities on the ground.
Scientists were also urged to improve their forecasts of the location and timing of ash clouds, and to reduce inconsistencies in such forecasts made in different parts of the world.
Probably the best news from the conference was that the formal procedures put in place a decade ago -- to quickly report significant volcanic activity and locations of ash clouds to pilots in the cockpit -- work well when they are followed. There was wide agreement that the procedures need to be rigorously followed to keep aircraft and ash away from each other.
Eruptive activity at Pu`u `O`o continues. The Banana flow, which breaks out of the Mother's Day lava tube a short distance above Pulama pali, is entering the ocean off the 2002 Wilipe`a lava delta. The national park has marked a trail to within a short distance of the active lava delta, and thousands have been enjoying the show. In addition, lava has been visible between Pulama pali and Paliuli for the past several weeks. Eruptive activity in Pu`u `O`o's crater is weak, with sporadic minor spattering.
One earthquake was reported felt on the island during the week ending July 21. A small, magnitude-1.5, earthquake was felt in Mountain View at 9 a.m. on July 15. The earthquake was centered 5 km (3 miles) west of Kilauea's summit at a depth of 3 km (2 miles).
Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity was down from its level of the previous week, with 5 earthquakes located in the summit area during the past week.
Updated: August 11, 2004 (pnf)