| BlueSky Business Aviation News | ||||||||||||||||||||||||||||||||||||||||||||
| . | ||||||||||||||||||||||||||||||||||||||||||||
That was the largest single interruption in air travel since World War II. This year, it's Grímsvötn, another Icelandic volcano. Some people, stranded air travelers in particular, are no doubt wondering if our concern with the problem of volcanic ash is wildly overblown. It isn't.
The watershed event Speedbird 9 ("Speedbird" is the callsign of British Airways aircraft, originallly the callsign of Imperial Airways - Imperial begat British Overseas Airways Corporation in '39 and BOAC begat British Airways in '74) was a watershed event. While neither the first (a Garuda DC-9 was apparently the very first commercial jet to fly through a volcanic cloud) nor the last (there was another one in the same area some thirteen days after Speedbird 9's incident), it does mark a change in the level of awareness of both airlines and air traffic regulators. Ash clouds are now tracked as best we can, and aircraft are routed around the clouds, or grounded if there is no way around. This is done to avoid the incredibly expensive repairs to the aircraft, true, but also to protect passengers. Just because the crews have so far been able to safely land all of the aircraft disabled by ash clouds doesn't mean that we will always be lucky. It pays to be safe. Digging in Let us take a deeper look at the issue. The word "volcano" we get from the Romans. There is a small island off the north coast of Sicily that has a volcano. The Classical Greeks named it Therassía and Thérmessa, which means "source of heat." It sounds classier in Greek. The volcano was the chimney of the workshop of Hephaestus, the lame god of blacksmiths. In that era, the Bronze Age, tin wasn't so easy to get, only minor deposts were found in Italy (none in Greece), but arsenic was often found in association with copper ore--making it cheap and readily available, and arsenic will harden brass into bronze, but at a pretty awful price for the smith. Arsenic poisoning--arsenicosis--results in muscle cramping (among other symptoms) which is where the lameness came from. Since smiths were often lame from arsenicosis, the god of smiths must also be lame, right? By the way, the fire that Prometheus brought us came from the forge of Hephaestus, that fire being the mythical representation of civilization and knowledge. It's still an open question what we will do with that forbidden gift. Following the Greeks, the Romans basically just overlaid their Latin words on top of Greek concepts, so Hephaestus became Vulcan, and the island became Vulcano. That name forms the basis for the word "volcano" in most European langauges. Now that we have a name, what does it mean? Before we can really define volcano, we need to understand something about planetary geophysics. I know this is why you read my column. We have volcanos throughout the solar system, but they require a planet (or moon, in the cases of Io and Europa) with a hot (relatively speaking) liquid core and a cold (in comparison) hard crust. Cutting to the chase, when the crust cracks all the way down to the hot liquid part, some of that hot liquid squirts onto the cold surface. (For some reason, this reminds me of the myth of Hephaestus and Athena.) This cracked part where the hot liquid squirts up is the volcano. Geologists take great joy in making it sound very complicated. On to the social issues Volcanos were not all created equal. There are three basic kinds, cinder cones, shield volcanos, and stratovolcanos. The cinder cones, to quote Douglas Adams, are mostly harmless. They are often found on the slopes of shield volcanos and stratovolcanos and are usually pretty small. Essentially, they throw out cinders and lightweight rocks to form a kind of loose, unconsolidated cone, hence the name. They rarely eject lava as a result of that same loose structure. Shield volcanos are huge, and while not really harmless, tend not to be a problem for aviation. They may well erupt for decades, but the lava they eject has a low viscosity (in part because it's really really hot, but also because it's low in silica) and tends to run quite a long ways. While shield volcanos can be enormous--the largest volcanos in the world are shield volcanos--they are fairly flat looking, generally around 1/20th of their width in height. It's the same on Mars, where we have discovered the largest volcanos in the solar system, and they, too, are shield volcanos. The Goldilocks of volcanos is the stratovolcano. This is the monster under the bed. If we are having an issue with volcanic ash clouds, it's a pretty safe bet that at the bottom of it we will find one of the stratovolcanos. Eyjafjallajökull, the Icelandic volcano that shut down air travel in 2010 is a stratovolcano. Mount Galunggung, the volcano that almost brought down Speedbird 9, is a stratovolcano. Mount Vesuvius, the one that buried Pompeii, is a stratovolcano. See a pattern in there? The stratovolcano differs from the shield volcano primarily (for our purposes) in the nature of its lava. The shield volcano has a very runny kind of lava, very low viscosity, that allows it to move relatively easily. The lava from the stratovolcano is sticky with a high viscosity (oodles of silica, as a rule), and it doesn't run well at all, leading to all manner of problems inside the volcano, not least of which is that it prevents gasses from passing through easily. This causes the gas pressures to build up to very high levels, which leads to explosive eruptions, which drives the light, finely divided particles called ash high into the air where they become a problem for us in aviation. Stratovolcanos also have that rugged volcanic mountain look. Kinds of eruptions Cinder cone volcanos have what are called Strombolian eruptions--named after Mount Stromboli in Italy where they were first studied.These are fairly anti-climactic, tossing hunks of red hot rock a few hundred feet into the air. This can go on for literally thousands of years. But, it's not that big of a deal to us. Shield volcanos have what geologists call a Hawaiian eruption, which is a mild, low-key sort of event without much in the way of ash, but they do result in positively enormous amounts of lava. Mauna Loa, the largest of the earthly shield volcanos has ejected so much lava over the ages (more than 18,000 cubic miles--yes, cubic miles) that the earth's crust has actually bowed significantly under the load.
Often, the very first part of the explosive eruption is classified as phreatomagmatic. As an engineer, there is no way I could not like this word. A phreatomagmatic eruption is one where the ground water is involved--flash heated to steam, taking the pressure in the volcano above what it can hold, resulting in a explosive opening to a longer-term, Plinian eruption, which can (and has) driven ash up to 90,000 ft in the atmosphere. Grímsvötn's recent eruptions are primarily phreatomagmatic because it actually lies under a sub-glacial lake. What can be done Things really are getting better. At first, we knew nothing, we just flew until the motors stopped turning, which is unnecessarily dramatic. Then we stopped all air traffic in areas that have ash clouds, a bit of an over-reaction some say. Now, we are exploring exactly how close we can fly, what concentration of ash can be tolerated, what operational procedures are necessary, what regulatory oversight is appropriate, what our maintenance procedures can do, and how to predict the location of these ash clouds and what ash-load can be expected along the flight path. In 1991, nine Volcanic Ash Advisory Centers (VAAC) were established around the world to track ash clouds and provide the best possible forecasts of where they will be and what ash-load can be expected. Europe, Africa, and western Asia is covered out the Toulous VAAC. The US, Central America, and South America down to central Brazil is covered by the Washington VAAC. London VAAC, of course, have been getting quite a workout since they monitor Iceland. Each VAAC area of responsibility is divided up into Flight Information Regions (FIR). All of this is done by ICAO, which is an agency of the United Nations. This is really important work and will only become more important over time as air traffic increases. The future Obviously, we cannot control volcanos any more than we can control hurricanes. These are listed as forces of nature for a reason. Nor can we yet design and build an ash-proof airplane nor even an ash-proof engine, so, our only strategy at this point is see and avoid. What we can do is continue working on improving our ability to forecast the location of the ash plumes, and I hope that someone is working on a better way to detect ash plumes, especially at low ash-loads that are hard to see, but still end up damaging the engines. It is a long-term project and it doesn't sound very sexy, but it really is the right thing to do.
Terry Drinkard is currently consulting on an aviation start-up. His interests and desire are being involved in cool developments around airplanes and in the aviation industry. Usually working as a contract heavy structures engineer, he has held positions with Boeing and Gulfstream Aerospace and has years of experience in the MRO world. Terry’s areas of specialty are aircraft design, development, manufacturing, maintenance, and modification; lean manufacturing; Six-sigma; worker-directed teams; project management; organization development and start-ups. Terry welcomes your comments, questions or feedback. You may contact him via terry.drinkard@blueskynews.aero Other recent articles by Terry Drinkard:
|
||||||||||||||||||||||||||||||||||||||||||||
