Many remember the six-day period in May 2010 when an explosive eruption of Eyjafjallajökull volcano in Iceland shut down air traffic to and from Europe. It was the largest air-traffic shutdown since World War II, stranding millions of passengers not only in Europe, but across the globe. David Pieri is a research scientist at the Jet Propulsion Laboratory in Pasadena, California. He uses an instrument called ASTER aboard NASA’s Terra satellite to measure infrared radiation from volcanic ash, with the goal of keeping airplanes safe. Pieri spoke more about why volcanic ash is so damaging to aircraft engines, and about keeping planes safe by watching volcanoes from space, with EarthSky’s Jorge Salazar.
Why study volcanoes from space?
Volcanoes have been a threat to humanity since people first walked the Earth. And you can think back to how Pompeii was completely buried during an eruption of the volcano Mount Vesuvius in the year 79 A.D. – the ash, hot rock and noxious, terrible, toxic gases coming out of the Earth. These things still happen. They can be very big, like the Pinatubo eruption in 1991, which pushed ash up into the stratosphere and had global effects on air traffic and air quality, as well as the environment locally around the volcano.
Volcanoes are big, dangerous features that manifest the internal energy of the Earth at the surface. We want to know about them. In the old days, volcanologists – geologists, basically, who specialize in volcanoes – would operate from the ground, sometimes from airplanes. And then, with the advent of satellites and orbital surveillance of the Earth, of course it was natural for people to want to watch these eruptions and the result of the eruptions from orbit.
The mission that I’m on is called ASTER – for Advanced Spaceborne Thermal Emission and Reflection Radiometer. It’s a joint mission with the Japanese. We have a number of tools from orbit. We can look at these big eruptions and see things on the ground down to 15 meters (45 feet) across. Volcanoes often happen in remote areas, but we can detect them and monitor them, to understand how much material they’re putting in the atmosphere.
Basically, we look at volcanoes from space and try to combine our space observations with observations from the ground and from airplanes.
Why are volcanoes so dangerous to aircraft?
Small eruptions that put out a little bit of gas or a small amount of ash are not usually dangerous to aircraft, if there’s not an airport close to them. We get concerned when we have a large, explosive eruption.
We’re taking a Mount St. Helens, a Pinatubo, even bigger ones than that. They’re erupting at thousands of cubic meters per second with enormous volumes of material coming out of a pressurized volcano. Volcanoes are pressurized by gas – mostly carbon dioxide, water vapor, but also sulfur dioxide – that comes out at these enormous eruptions with vertical updraft rates of hundreds of meters per second.
These plumes can reach up to at least 10,000 meters, which is above 30,000 feet. Pinatubo went as high as 150,000 feet, if you can imagine that. Typically the eruption or burst occurs quickly, or it can be sustained for minutes or hours – maybe even days.
The material gets up in the air, and the atmospheric winds take it, particularly in the stratosphere at about 30,000 feet. Unfortunately, that’s the most efficient operating altitude for aircraft, between 20,000 and 40,000 feet. If you’re unlucky enough to penetrate a plume in an aircraft, you can have simultaneous, all-engine failures. This happened a couple times in 1983, with the Galunggung eruption in Indonesia. And then there was the Redoubt eruption in 1989. It’s a particularly harrowing case.
On December 15, 1989, a KLM aircraft was en route from Amsterdam to Tokyo. And in those days, it was typical to make a refueling stop in Anchorage, Alaska on that route. This airplane was descending northwest of Anchorage Airport into what looked like haze. The volcanic plume from the Redoubt volcano was predicted to be northeast of the volcano. The airport expected the plume to be away from the aircraft.
So the pilot descended into what looked like a haze layer. She got a smell of sulfur in the cockpit, and she then realized that her engines were failing. Basically four engines flamed out. She lost power, and the plane started to descend. They frantically tried to restart the engines. They had multiple engine restarts. I think they tried seven times, unsuccessfully, falling from 25,000 feet. They got one engine relit, and then the other three came online, and they got the engines restarted. They leveled out at about 12,000 feet after about a minute and a half. They leveled out just above the mountains, about 500 feet above the terrain. There were about 285 people on board. It was a very, very close call.
What made the engine stop?
There are a couple of things that go on in jet engines when ash gets sucked into them, especially with the newer engines, which operate at very high temperatures.
Ash is very finely ground-up rock. It’s very abrasive. So you get abrasion in the engine. That’s not good, especially with the newer high-temperature engines. It can interfere with the combustion process. The ash concentration can be high enough that it affects the fuel injection mechanism in the engine. So the engine stops combusting.
On top of that, ash will melt on the turbine blades. Each turbine blade is like Swiss cheese, because the engine is constantly forcing air through the turbine blades to cool them. These blades are coated with special coatings and also are drilled with holes. And the ash will come in and flash melt on the blade. Then it’ll get cooled by the cooling air and solidify. You get a ceramic glaze on the blade. And now the blade can’t cool itself.
So you have two kinds of hazards. You have the prompt hazard of the cessation of combustion in the engine – so the engine just stops. If you have high ash concentrations, that’ll happen.
But even if the engines don’t stop running, you get these turbine blades that are now clogged and can’t cool themselves. Then, say, 50 or 100 hours after the incident – and you might not even have known you’ve flown through ash, if it’s a very thin plume – you could have metal fatigue and possible failure.
What’s the solution?
Basically, as much as possible, you want to keep airplanes out of volcanic ash. The practice has been to vector aircraft around these plumes when they occur, such as from Mt. Cleveland volcano, Shishaldin volcano, Redoubt, Augustine. These are famous names to volcanologists. When these volcanoes erupt, the FAA and the National Weather Service tend to route the aircraft around the volcanic plumes and clouds.
And so that’s a pretty good solution – sort of a zero-tolerance policy.
But it doesn’t always work. What happened in Europe in 2010 when Eyjafjallajökull eruption put ash into European airspace, European airlines had nowhere to go. The ash was coming over major metropolitan areas of Europe, a major intrusion into the airspace. So they were shut down completely.
There was a big discussion at the time about what safe levels of volcanic ash really were. They couldn’t just route the planes around the ash, although, at some point, they were tentatively trying to fly with low levels of ash. There was a big discussion at that time about how you estimate the amount of ash in the air, how accurate the satellite observations were, what ash really means in terms of nuts-and-bolts aircraft operation.
Who is responsible for making this sort of decision?
The International Civil Aviation Organization and the World Meteorological Agencies have divided the world up into about 10 zones. Each zone has a Volcanic Ash Advisory Center – what’s called a VAAC – that’s responsible for that zone.
We have two in the U.S., one in Anchorage and one in Washington. In Europe, the two main ones that were involved in the Iceland incident were the London VAAC and the Toulouse, France VAAC.
Let’s face it, the average person walking around in the United States or Europe is not going to get hit with a volcanic blast. That’s almost inconceivable. But people from the U.S. or Europe might face a threat when they fly.
And so, in modern times, this hazard has been dispersed into vulnerable air space that the airlines like to use and that other commercial carriers and military carriers also use. We’re now susceptible and vulnerable in the modern society to this pervasive hazard of ash.
There are over 1,500 volcanoes around the world that are considered to be active at any time. Working with the Terra satellite, our job is to figure out ways to detect volcanic ash, track it, predict where it’s going to go and also to mitigate the effect to airplanes.
Tell us more about how the instruments on NASA’s Terra satellite monitor volcanic ash.
We have several dozen volcanologists who are experienced in remote sensing as well as volcanology. I’m one of them. And from the Terra satellite platform, we have three main instruments.
When you look down at Earth, you have two kinds of radiation that come into the instrument. With your eyes, when you look at something, you’re seeing light – energy that’s reflected off the surface at various wavelengths – and your eye and brain perceive it as color. So you have the visible spectrum, and certainly Terra can get good visible images of a volcano. If we have an eruption column, we can see it in visible wavelengths, and we can actually take stereo pictures and create a three-dimensional image with ASTER.
And then we have infrared capability – often basically heat radiation coming up from the surface of the Earth. We take a number of different bands so that it looks like heat in color. Basically, we’re taking the temperature of the Earth. And so if you have a volcanic eruption, at the beginning of the eruption, it can be very hot. Lava flows are throwing off a lot of heat. So the infrared capability with ASTER allows us to map these heat features in detail.
We’re looking at high spatial resolution so we can resolve, for instance, the summit craters of volcanoes. We can resolve individual lava flows. We can resolve areas where vegetation has been destroyed. We can look at areas of devastation with ASTER. It’s a pointable instrument. It’s not always on. We actually have to plan to look at a target ahead of time. That makes it a little bit of a guessing game sometimes.
One of the other instruments on Terra is the Moderate Resolution Imagine Spectrometer (MODIS). It looks through the visible near-infrared and thermal infrared as well, but at much lower spatial resolution, much of it at about 250 meters per pixel. Where ASTER can only see an area that’s 60 by 60 kilometers across, MODIS can look at areas thousands of kilometers across. And it looks at the whole Earth every day. Where ASTER gets little spaghetti strips and individual postage stamps targeted, MODIS is a much more of a survey-type instrument, which sees large parts of the Earth at once. And during the course of a day it builds up entire coverage.
The third instrument is the Multi-angle Imaging SpectroRadiometer (MISR). It has multiple look angles, and it can create a visible and dynamic three-dimensional image – the actual sight of the eruption. It has multiple look angles as it progresses in orbit. That’s important because you can make three-dimensional images of the features that you’re looking at, especially airborne features. MISR was mainly designed to look at aerosols, which are particulates in the atmosphere such as water droplets and dust. That’s important for big explosive eruptions, which put a lot of aerosols into the atmosphere.
That’s kind of a thumbnail sketch of what we do with the Terra satellite. It’s been quite effective, both in looking at precursor volcanic phenomena, such as hotspots or some of the craters that begin to light up possibly a month or two ahead of eruption. Plus it looks at the results of the eruption, and other things. Terra and its instruments aren’t just for volcanology. We look at a variety of Earth surface phenomena.
Thanks, Dr. Pieri. Want to leave us with any final thought?
Sure. It’s that volcanoes are not a one-shot deal. People have had to relearn this lesson since the days of Pompeii. The volcano that’s active today is most likely the one that was active yesterday. Volcanoes might be rare in an individual lifetime, but, when they happen, they are big and dangerous.
In the future, Terra-like satellites – with even more continuous coverage – are going to become more and more important for detecting eruptions and understanding the environmental parameters under which we operate aircraft.
Our response now is hopefully a lot more considered, and a lot more comprehensive, than the poor people in Pompeii who faced the eruption of Mount Vesuvius in 79 A.D.