Sunday, 25 April 2010

Roman God to Icelandic Witch

For those who were caught up in the travel problems caused by a cloud a volcanic dust, there’s not much consolation in being told it could have been worst.

The term “volcano” was first used by the Romans to describe Mount Etna, the mountain they believed to be the forge of Vulcan, their god of fire. It was Vesuvius in AD 79 that devastated the towns of Pompeii and Heracleum. Vesuvius, classified as a dormant volcano, last erupted in 1943.

Active volcanoes erupt on a regular basis every so often; some are permanently active. Dormant volcanoes have not erupted for 25 years or over; they will erupt again soon or may be classed as extinct if they have not erupted for centuries; extinct volcanoes have come back to life after centuries of inactivity.

Volcanic activity is associated with movements of the Earth’s tectonic plates. Volcanoes occur within zones within or at the edge of the tectonic plates. About 90 percent of all volcanoes exist in the so-called Ring of Fire along the edges of the Pacific Ocean.

Iceland’s Mid Oceanic Ridge volcanoes occur where two tectonic plates are diverging and form along a line of fissures. Laki, in 1783, came from a 15-mile long fissure. The eight month eruption of lava, dust, acidic and poisonous gas killed almost all of Iceland’s sheep and cattle. One-quarter of the population died of starvation or were killed by the toxic fumes.

The Laki eruption resulted in what has been called Britain’s greatest natural disaster. Dust clouds obscured the sun during the summer, flash floods occurred and there was an increased number of deaths. The bad summer was followed by one of the coldest winter on record.

If Laki was a killer it was dwarfed by Tambora in Indonesia in 1815 when an estimated 92,000 died. Its effects were felt as far away as Europe and North America. The devastating effects of Tambora are said to have inspired Bryon’s gloomy poem “Darkness” and Mary Shelley’s “Frankenstein.”

More people witnessed Tambora than any other eruption but Krakatau, also in Indonesia, in 1883 generated the loudest sound from the release of an estimated 200 megatons of energy, the equivalent of 15,000 nuclear bombs.

The late Bronze Age eruption of Santorini off Greece was very similar to that at Krakatau; the central highland of the island collapsed to generate the modern caldera which forms the three island archipelago of Thera, Therasia and Aspronisi. The myth of the lost city of Atlantis may be based on the collapse of Santorini.

Air passengers who doubted the wisdom of the flying ban following the April 2010 eruption of Eyjafjallajökull should be reminded of what has happened before. On 24 June 1982 a British Airways 747 flew into an ash plume from Indonesia’s Mount Gulanggung. All four engines failed in turn, the plane lost 23,000 feet in height. Fortunately all four engines restarted after it glided clear of the ash cloud. Three weeks later three of the four engines shut down on a Singapore Airlines 747 in the same area.

In December 1989 a KLM 747 flew into a volcanic ash cloud from Mount Redoubt in Alaska The aircraft entered the cloud at 25000 ft; all four engines failed. The plane descended for more than 14000 ft before the crew managed to restart the engines.

But perhaps what we should fear most is the larger and more dangerous Katla volcano, named after a witch in Icelandic legend, adjacent to Eyjafjallajökull. In the past 1,000 years, all three known eruptions of Eyjafjallajökull have triggered subsequent Katla eruptions.

1 comment:

DW said...

As usual, Bob, a fascinating insight into the world around us, even if it is a bit doom-laden in that last paragraph.

I don't think I need worry about the dust. The tobacco's done so much damage, a bit of volcanic ash won't make it much worse.