About 100 miles southwest of Anchorage, Alaska, the ground around Mount Redoubt has begun to shake and a smell akin to rotten eggs tinges the air. The last time this happened the 10,197-foot volcano erupted for five months, venting hydrogen sulfide and sulfur dioxide gas and spewing ash into the air. Professor Johan Varekamp remembers it well. He was among scientists who analyzed the direct effects of the 1989-1990 eruption.
The ash he examined was ejected more than 40,000 feet into the sky; the resulting ashfall covered nearly 8,000 square miles of the surrounding landscape.
“As is often quoted in the newspapers, ash is an unpleasant substance for human lungs as well as jet engines, given the sharp edges of small glassy ash fragments,” says Varekamp, the Harold T. Stearns Professor of Earth Science, who studies volcanoes and their effects. “Inhalation of volcanic ash leads to lung irritation and possibly lung damage. It is often compared to silicosis, which is a lung condition that many workers in quarries had by inhaling quartz dust, but this is technically somewhat different.”
Mount Redoubt is a stratovolcano, similar to Mount Saint Helens in Washington, Mount Fuji in Japan and Mount Vesuvius in Italy. Its activity is caused by pressure and friction from the collision of two massive tectonic plates. In this case, the Pacific plate is sliding under the North American plate, a process known as subduction. The addition of subducted seawater at great depth in the earth leads to melting and magma formation, and the magma rises and ultimately blows a hole through the mountain with a volcanic eruption.
This happened at least three times in the 20th Century at Mount Redoubt – 1902, 1966 and 1989-90. The 1989-90 eruption blanketed the area around the mountain and in Anchorage, Alaska’s most populous city, with fine volcanic ash that caused extensive property damage, disrupted international air traffic, and made it difficult to breathe.
Varekamp’s own work on these ashes focusses on the ultimate sources of all that emitted sulfur and chlorine – old subducted seawater or deeper sources. He analyzed the ash from the last eruption of Mount Redoubt and thinks that, if it erupts again, the volcano could create as much damage as it did before, if not more.
“Though one thing that shouldn’t happen is that an eruption this time around won’t be taking down any jetliners,” Varekamp says. “A protocol has been put in place for that.”
Varekamp is referring to an event that occurred during the volcano’s last eruption. Anchorage is a major hub of air travel coming from Asia and the Pacific Rim. In 1989 when Mt. Redoubt began spewing volcanic ash, KLM flight 867, a 747 jetliner carrying more than 200 passengers, had a flight path into the ash plume. The ash caused the engines to fail and the plane began plummeting to the ground. It fell more than 2 miles before the crew was able to restart one of the engines and make an emergency landing. No lives were lost but since then the state of Alaska and the Federal Government have created an air traffic alert system for volcanic eruptions using the Alaska Volcano Observatory (AVO). There are now nine such volcanic ash advisory centers around the world to advise the international aviation industry of the location and movement of clouds of volcanic ash.
One component of a volcanic event that more people are aware of today is the possible environmental impact of an eruption that can release thousands of tons of ash.
“Hot ash flows can be very devastating,” Varekamp says. ““They flow down the mountain quite quickly and would certainly destroy anything in their path. Beyond that, mud flows can follow river valleys and, depending on the amount of watery mud, can cause significant environmental damage as well, as observed during the 1980 Mount Saint Helens eruptions.”
Varekamp also speaks of the ash injected into the air by the volcano. During Mount Redoubt’s last eruption, much of the landscape as far as 200 miles away from the mountain was covered in several inches of the fine volcanic ash.
“It falls from the sky like snow,” he said. “Along with possibly damaging lungs and fouling the function of engines and other machinery it will scratch surfaces like glass if you, say, turn on the windshield wipers of your car. And of course, unlike snow, ash will not melt. You need some sustained rainfall to wash it away, or a clean-up process in more populated areas.”
Varekamp says scientists do not expect an eruption to create a large negative environmental impact beyond the land and waterways directly surrounding the mountain, but that the intensity of the volcano’s upcoming activity cannot be known exactly before hand. Despite sophisticated forecasting techniques, there is still some element of surprise.
For instance, in 1991, Mount Pinatubo in the Philippines began rumbling and steaming much the same way as Mount Redoubt is today, but the ultimate eruption discharged so much ash and sulfur-bearing gases so high into the atmosphere that it created one of the coldest winters on record worldwide in 1992.
“That is the nature of volcanoes,” he says. “This could be a relatively modest event like the one in 1989 through 90, or there could be much more pressure building up than we suspect and the eruption could be much more significant.”
The current activity is being monitored by the AVO, which is posting regular updates. Steven McNutt ’77, one of the worlds leading volcano-seismologists, is based at the University of Alaska, Fairbanks, and is also a staff member at the AVO. He is been part of the team monitoring Mount Redoubt’s activities.
“I am intimately involved with Redoubt,” McNutt said recently via e-mail and recounted that during the week of January 25, when the mountain’s seismic activity began increasing, he “spent four days on the Kenai Peninsula installing detection equipment with colleagues.”
The Kenai Peninsula is located directly across from Mount Redoubt.
For more information, the AVO is providing periodic updates here.