http://www.bbc.co.uk/news/world-latin-america-32434490
https://youtu.be/_MdUQY6xQG4 (this is the source of the BBC video)
The volcano close to Calbuco, Puerto Varas, Los Lagos Region, Chile, South America last erupted in 1972. Last Wednesday, 22 April (and again Thursday, then again today) it erupted once more. Countless millions of tons of ash are being forced 6 miles (10km) up into the Stratosphere. Air travel has been cancelled & the ash has caused at least one building to collapse. The local town is now abandoned.
Human communities have always gathered around volcanoes, and that seems extraordinary when we see the destruction caused during an eruption. However, those self-same eruptions place vital trace minerals into the soil, which causes the land to be immensely fertile. The action of the volcanoes at deeper levels is also responsible for valuable mineral seams that have allowed the later industrial ages to flourish. Further, the discovery of life within the sulphur-rich, scaldingly hot water that up-wells at the bottom of the oceans at tectonic boundaries has led to theories that volcanoes may even be the source of life on earth.
So, volcanoes have been the gift that keeps giving to all organic life. However, in the short term they are also the source of extraordinary destruction. Very close to the volcano that damage can come from lava. Still close, but over a greater distance, the greater danger comes from the ash. The most obvious danger is from large particles of blue-grey ash that quickly fall from the ash-cloud:
This ash is heavy, and can build up a thickness on roofs that will quickly overwhelm them. That has already happened to a Chinese restaurant (“Bombon Oriental”) in Puerto Varas. Elsewhere, entire families are scrabbling to clear their roofs with shovels & brushes:
One of the minerals collected in volcanic regions is sulphur. All of the sulphur at the surface of the planet comes from volcanoes. Sulphur is also a vital component for life (together with other incendiary elements like phosphorus), but is also poisonous if present in anything other than the smallest amount. But let’s get back to the ash...
The big lumps of ash are obviously dangerous because of their weight. One thing that may seem strange at first is that the finer ash is also dangerous because it is so small. Our noses will filter out lots of dirt, but they cannot filter out the very fine ash - it will pass straight into our lungs (those masks? useless at filtering out the fine ash or sulphur).
The final thing to mention is the ash-cloud punching up into the stratosphere.
The interface between the troposphere and the stratosphere.
The temperature gradient in the region close to the ground (the troposphere) is “getting colder as you go up”.
The temperature gradient in the stratosphere is “getting hotter as you go up”.
The tropopause is the part of the atmosphere where the temperature gradient changes. Normally, the air from below cannot penetrate up into the stratosphere, which makes it a calm place to be, and that is part of the reason that aeroplanes fly there. That all changes during an eruption of a volcano like Calbuco.
The top photograph was taken early near the start of the eruption. However, it is really obvious in the uTube video that the ash-cloud is forcing itself up beyond the tropopause and into the stratosphere. That is immensely dangerous for aircraft, and is why all air-flight has been stopped. To know why, you need to go back to the climatic eruption of Mount Pinatubo, Philippines, in June 1991.
The effects of volcanic ash on modern jet aircraft were well known before the Pinatubo eruption, but few took it seriously. Therefore, when it began to erupt on April 2, and even after the climatic eruption of June 15, no action was taken to prevent any aircraft flying through the downstream ash-cloud. At least 20 commercial aircraft were damaged, and two Jumbo Jets had to have all 4 engines replaced. Here is one official report from a 747-400 (Jumbo Jet) at 5:40pm June 15:
Aircraft encountered ash cloud at 29,000 ft at approximately 600 nm west of volcano. Crew observed St. Elmo’s fire on the windshield and a scent similar to an electrical fire in the cockpit for 6 to 8 min as they went through the ash. There was no abnormal indication in the cockpit. The crew observed a green echo, which seemed to be ash on weather radar, but it disappeared when they were clear of the ash. Flight attendants reported thin (whitish) fog in the cabin, most dense in the upper deck compartment, followed by the forward cabin. The flight was continued to Tokyo, where engine inspection revealed that all four engines were damaged and were replaced. First-stage nozzle guide vane cooling air holes were 70-80% blocked. Other damage occurred to the cockpit windows, cabin windows, Pitot static probes, landing light covers, navigation lights, and all leading edge areas.
Writing in May 1993 the CAA reported that “Since 1980, at least seven encounters between jet-powered air-craft and volcanic ash clouds have resulted in temporary engine failures”. I remember reading about this next one at the time. Try to imagine what a “powerless descent of nearly 25,000 feet” (7.62km) must feel like to a passenger in that plane:
In 1982, two Boeing 747-200 passenger jets encountered ash at night from separate eruptions of Galunggung Volcano in Java, Indonesia. In each case, pilots observed St. Elmo’s fire, noted the acrid smell of sulphur gas, observed fine dust quickly filling the cabin and experienced moderate turbulence while in the ash-cloud. In both cases, volcanic ash entered the jets’ engines and caused surging, flameout and immediate thrust loss of all four engines. After powerless descents of nearly 25,000 feet, the pilots of both aircraft eventually restarted all engines and landed safely at Jakarta. Both aircraft suffered extensive damage to engines and exterior surfaces.
The Pinatubo eruption was so extensive that all authorities finally began to work together. Procedures were put in place so that those with information on the spread of the ash-cloud actually informed everybody else, plus the aviation authorities kept aircraft out of danger.
--------- Alex Kemp