26 December 2010

Top 10 worst eruptions of all time

By
Cosmos Magazine
Scientists have improved capabilities for predicting some volcanic eruptions, but only if they know which mountains to monitor. Long-dormant volcanoes can awaken unexpectedly to wreak havoc. We count down the top 10 worst eruptions.
Eyjafjallajökull

Eyjafjallajökull erupting on 27th March, 2010. We rate it as one of the worst eruptions in history. Credit: Wikimedia

SYDNEY: “There is little that society can do in the face of the largest known volcanic eruptions, and it is a good thing that they happen very rarely on a human timescale,” says James White, volcanologist at the University of Otago in New Zealand. Scientists have improved capabilities for predicting some volcanic eruptions, but only if they know which mountains to monitor. Long-dormant volcanoes can awaken unexpectedly to wreak havoc.

NYIRAGONGO, DEMOCRATIC REPUBLIC OF CONGO 1977
Volume erupted: 0.01 km3 of lava
Killing mechanism: lava flow

Situated along the Great Rift Valley, Nyiragongo had a lava lake in its summit crater, which burst during the night in January 1977. Runny lava flowed down its steep sides at rates of nearly 100 km per hour, quickly draining the lake. More than 70 people died.

Nyiragongo erupted again in 2002, sending flows toward the city of Goma and the shores of Lake Kivu. Because of volcanism in the region, Lake Kivu accumulates carbon dioxide in its waters, and a major disturbance of the lake could result in a suffocating release of CO2.

7. MOUNT VESUVIUS, ITALY, 79 AD
Volume erupted: 3 km3
Killing mechanism: ash, pyroclastic flows

Vesuvius is considered one of the most dangerous volcanoes, as large populations lie in the path of potential eruptions. In 79 AD, an estimated 16,000 people in the Roman cities of Pompeii and Herculaneum were killed by pyroclastic flows – fast-moving, surface-hugging flows of ash, rock, dust and gas at temperatures of up to 700°C. Vesuvius has erupted about 50 times since 79 AD, with the most destructive in 1631, killing about 4,000 people.

6. LAKI FISSURE, ICELAND, 1783
Volume erupted: 12 km3 lava, 1 km3 tephra
Killing mechanism: atmospheric dimming, acid rain, crop die-off

One of the largest known historical lava flows occurred from the Laki Fissure, where rifting is tearing Iceland apart. A 25-kilometre-long fissure erupted 12 km3 of lava over the course of seven months. In this case, it isn’t the size that made it devastating but the environmental effects. Huge amounts of sulfur dioxide added to the atmosphere created acid rain, disrupted regional climate and left a lingering fog shrouding parts of the Northern Hemisphere.

The resulting famine killed tens of thousands across Western Europe, including up to a quarter of Iceland’s population. The recent eruption of Eyjafjallajökull is insignificant in comparison to Laki. Whereas the 1783 eruption sent 120 million tons of sulfur dioxide into the lower stratosphere, Eyjafjallajökull emitted only a fraction of that and it only reached the troposphere, where it is shorter-lived.

5. PINATUBO, PHILIPPINES 1991
Volume erupted: Over 10 km3
Killing mechanism: ash, pyroclastic flows

Pinatubo awoke in 1991 after more than 450 years of quiescence. Prior to this eruption, the mountain’s dangers had been largely forgotten as its volcanic soils supported abundant agriculture. The eruption caused around 800 deaths, but tens of thousands were saved through monitoring and evacuation. Particulates shot into the atmosphere caused temporary ozone depletion and a global temperature drop of 0.5° C. Subsequent rainy seasons sent mudflows, or lahars, down its slopes.

4. KRAKATAU, INDONESIA 1883
Volume erupted: Over 20 km3
Killing mechanism: tsunami

Krakatau killed an estimated 36,000 people, mostly due to the tsunami, which reached a height of 37m. It also generated an atmospheric shock wave that travelled around the Earth seven times, and noise from the blast was heard up to 5,000 km away. Anak Krakatau (‘Child of Krakatau’) has been growing steadily through milder eruptions.

3. LAKE TOBA, INDONESIA, 73,000 YEARS AGO
Volume erupted: 500 km3 of ash
Killing mechanism: volcanic winter

This supervolcano in Sumatra formed a 35 x 100 km caldera when it exploded. The eruption sent the planet immediately into a ‘volcanic winter’, which is thought to have reduced the human population to less than 10,000 individuals.

2. LAKE TAUPO, NEW ZEALAND 26,500 YEARS AGO
Volume erupted: 1,170 km3 of tephra
Killing mechanism: island uninhabited

This large eruption, known as the Oruanui, formed the caldera that holds Lake Taupo in the centre of New Zealand’s North Island. This enormous volcano didn’t kill anyone, as the island was uninhabited at the time. But if it occurred today, it would be devastating.

“[This eruption] devastated almost all of the North Island, and buried everything from Christchurch northward and from Auckland eastward for hundreds of kilometres to the Chatham Islands, under a suffocating blanket of ash more than 10 cm thick,” says White. Taupo has had about 28 major eruptions since then, with the largest and most violent occurring around 186 AD.

“It will be a challenge to know when restlessness becomes a precursor to eruption, and a bigger challenge yet to predict the scale of a coming eruption,” says White.

1. SIBERIAN TRAPS 250 MILLION YEARS AGO
Volume erupted: Over 3 million km3
Killing mechanism: global warming

This huge expanse of flood basalts, which covers an area the size of Western Europe, represents one of the largest known volcanic events in the last half billion years of Earth’s history. The eruption is one of the likely causes of the Permian-Triassic mass extinction event, in which 95% of marine species and many terrestrial vertebrates, insects and plants died off. The eruption lasted for about one million years.

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