Friday, April 15, 2005

Volcano eruptions through history

Earthquakes, tsunamis and now, volcanic eruptions. We might wonder what the world is coming to,but history shows that worse catastrophes have taken place.

In April 1815, the world’s biggest and most destructive volcanic eruption occurred on the island of Sumbawa in Indonesia. The explosive Mount Tambora wiped out an entire ethnic group and the effects of its eruption changed the global climate, causing widespread crop failures that led to famine in North America and Europe. There were food riots in France and Switzerland, and in Ireland, 65,000 people died of hunger and a typhus epidemic. Hundreds of thousands of people died throughout the world as a result of one volcanic eruption, the event dubbed the Year Without a Summer.

The kingdom of Tambora, which had remained buried for centuries, has now been uncovered and the remains of what happened after the Mount Tambora eruption are being seen for the first time. The little-known global cataclysmic event and the discovery of the town of Tambora will be presented in a new Discovery Channel documentary, The Year Without Summer (premiering this Sunday).

Professor Haraldur Sigurdsson, the volcanologist featured in the documentary, said in a phone interview that the eruption of Mount Tambora sent a tremendous amount of volcanic ash and volcanic acid into the atmosphere. In fact, the column of ash and gases went as high as 42km into the stratosphere; it was the highest known eruption column on Earth.

“And that had a great effect on the solar radiation reaching the Earth’s surface,” said Prof Sigurdsson. “So it caused global cooling. And that created the Year Without a Summer.”
He said the theory of how the Year Without a Summer occurred had been proposed about 50 years ago, and now, evidence has been found of the acid and gases from the eruption in ice cores in Greenland and Antarctica, indicating the global spread of the material from this eruption.
“So not only did it spread throughout Indonesia and South-East Asia and Central Europe, it also reached the poles, both North and South,” he said. “And the correlation with Tambora is perfect in terms of timing. The event occurred in 1815, and the Year Without a Summer was in 1816 and 1817.”

He described the town of Tambora, which was discovered in August last year, as the “Pompeii of the East,” referring to the famous city of Pompeii that was buried and preserved by the ash from the eruption of Mount Vesuvius in Italy. He said people and objects were also found preserved by the volcanic ash in Tambora, and he believed the area will become an archaeological site in the future.

Prof Sigurdsson said an eruption of Mount Tambora’s magnitude will definitely occur again in the future, but it will be difficult to predict when and where. In fact, there is no global detection system available as far as volcanic eruptions are concerned, although satellite information can be used to monitor all volcanoes on Earth.

“You can determine whether a volcano is inflating or changing its shape,” he explained. “Usually before a very large eruption like (Tambora), the volcano will inflate. It actually increases in volume. When the magma moves up into the volcano, the volcano grows or inflates and bulges out. There is a need to have a global system for monitoring volcanoes, just as there is a need for a global system for monitoring earthquakes and tsunamis. Once that type of system is implemented, then one would be able to detect beforehand the likelihood of an eruption like Tambora.”

He said there are about 500 active volcanoes in the world today, and only about 20 are being closely studied.

“Many volcanoes will typically go through a very long period of repulse or quiet, maybe for hundreds of years, before they erupt,” he said. “In these volcanoes there is potential for a build-up of magma to a very large volume which may result in very dangerous eruptions. And these volcanoes are not necessarily the ones that are being studied today.”

Currently, three volcanoes in Indonesia – Mount Talang and Anak Krakatoa in Sumatra, and Tangkuban Prahu in Java – are showing signs that they are about to erupt. Asked what the magnitude of the eruptions will probably be, Prof Sigurdsson said they would be relatively small ones. But because Tangkuban Prahu is just outside of Bandung, it may be a significant problem for the people of that city and Java as a whole.

On whether the recent spate of earthquakes and the tsunamis of last year have anything to do with the volcanoes, Prof Sigurdsson said: “Volcanic eruptions and earthquakes are caused by the same process. Both of them are related to the movements of the floor of the Indian Ocean. The plate, called the Indo-Australian Plate, is moving north and being thrust underneath Sumatra and Java. But volcanoes don’t cause earthquakes and earthquakes don’t cause eruptions.”
Prof Sigurdsson added that major eruptions like Mount Tambora occur every 200 to 300 years. And since it has been almost 200 years since Tambora, the likelihood of such an eruption is even greater now.

How prepared are we for such a global event?

“There really is no preparation for this type of event other than the general civil preparation that is made in emergency situations,” he said. “There has been very little discussion as to how to respond to this type of event. In modern society, an eruption of this magnitude and its global effects would create tremendous political problems and great unrest in society.”

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