NYIRAGONGO

Mount Nyiragongo in the Democratic Republic of Congo is one of Africa's most active volcanoes.  The volcano, one of eight along the borders of Rwanda, the Democratic Republic of Congo and Uganda, has a long history of activity.

Nyiragongo was last active in 1994, when a lava lake reappeared in its summit crater.  The latest eruption is more serious. Lava from Nyiragongo can travel at 60 kilometres per hour (40 miles per hour). Bill Evans of the US Geological Survey said lava could react with gas in the lake, with catastrophic consequences.  "A hot lava flow flowing down into the deep waters of the lake could trigger this gas to come out very quickly."

"The gas is composed of carbon dioxide and methane; so it would come up and create a suffocating and yet flammable cloud that could engulf communities living around the lake."   There is no record of such an event at Lake Kivu in the past. However, in 1986, Lake Nyos in Cameroon released a cloud of gas, which killed more than 1,700 people.   Nyiragongo, and nearby Nyamuragira, are the two active volcanoes among the eight volcanoes in Rwanda, the Democratic Republic of Congo and Uganda.  Both are in the Virunga mountain range, which straddles the border with Rwanda. The pair are responsible for nearly two-fifths of Africa's historical eruptions.

Nyamuragira erupted early last year. It caused no casualties but cultivated land was burnt out by ash, trees were destroyed and some water supplies were polluted.

LAKE NYOS

In August 1986, the lake released a cloud of carbon dioxide, which hugged the ground and flowed down surrounding valleys to suffocate thousands of local villagers and animals.  More than 1,700 people died. 

In 1991 Scientists from the United States, France and Cameroon used a series of giant pipes to release carbon dioxide from deep down in the waters of the lake.  They said that pressure from the gas had built up again and “a similar tragedy could happen at any time”. 

The rare phenomenon also occurred at Lake Monoun in the same volcanic zone two years earlier killing 34 people.  According to some reports, the lake now contains twice as much carbon dioxide as was released during the explosion. Earlier attempts to siphon off the gas had to be abandoned for financial reasons.

Autosiphon project

The process termed autosiphon was tested for the first time in 1995 by French geochemist Michel Halbwachs.  He told a news conference that a long pipe was inserted 210 metres (690 feet) into Lake Nyos. "The very long pipe spews 90% carbon dioxide and 10% water to a height of 50 metres," he said.

The Nyos Organ project, as it is known, involves inserting 12 pipes into the lake. "By doing so, the accumulated carbon dioxide in the depths of the lake will be gradually released at very high altitude in the atmosphere and will not be dangerous to people living nearby," he said.  The project will be monitored by satellite. Cameroon's minister for scientific and technical research, Henri Hogbe Nlend, said the project would cost about $2.8m.  He said that the US Government had already contributed $450,000.

PINATUBO

The Philippine authorities evacuated more than 40,000 people from Botolan in the north of the country in case the daring attempt to drain the volcano's lake went wrong.

The lake, in the crater of Mount Pinatubo, had been filling with rainwater since it was created in an eruption 10 years ago.  Scientists feared that unless they emptied it in a controlled manner, it could breach the volcano's rim and flood the surrounding area.  Raymundo Punongbayan, director of the Philippine Institute for Volcanology and Seismology, said a five-metre-wide (16 feet) channel had been dug from the crater's edge.

A "plug" of earth has been left in place, ready to be dislodged when the order to drain the lake is given, expected on Thursday morning.

Mr Punongbayan said there was still a 20% chance of the operation going wrong.  In this scenario, a surge of water could collect mud and bury villages in several metres of debris.

"That's why we want people to evacuate," Mr Punongbayan said.  If the operation goes according to plan, 24 million cubic metres (five billion gallons) will be drained off in the first 24 hours. 

The problem has its roots in Mount Pinatubo's 1991 eruption, when 800 people were killed.  The volcano's top was blown off during the eruption, leaving a hole covering five square km (two square miles). Despite government warnings about the evacuation, not everyone intends to leave.  Faustino Corum, a retired government assessor, told Reuters news agency he was staying put.  "I will be able to see the waters coming even if they are still kilometres away. That will give me enough time to run," he was quoted as saying.

MT. PELÉE 

Although in January 1902 Mt. Pelée began to show an abrupt increase in fumarole activity, the public showed little concern.  This changed, however, on April 23 when minor explosions began at the summit of the volcano. Over the next few days, St. Pierre was rocked by earth tremors, showered in ash, and enveloped in a thick cloud of choking sulfurous gas.  These nightmarish conditions deteriorated further when the city and outlying villages were invaded by ground-dwelling insects and snakes driven from the slopes of Mt. Pelée by the ashfalls and tremors.  Horses, pigs, and dogs screamed as red ants and foot-long centipedes crawled up their legs and bit them.  Thousands of poisonous snakes joined the fray.  An estimated 50 humans, mostly children, died by the snake bites, along with some 200 animals.

As the summit eruptions intensified, water in the Etang Sec crater lake was heated to near boiling.  On May 5, the crater rim gave way, sending a torrent of scalding water cascading down the River Blanche. The hot water mixed with loose pyroclastic debris to generate a massive lahar with a downslope speed of nearly 100 kilometers per hour. This large volcanic mudflow buried everything in its path. Near the mouth of the river, north of St. Pierre, it overran a rum distillery, killing 23 workmen. The lahar continued into the sea, where it generated a three-meter-high tsunami which flooded the low-lying areas along the waterfront of St. Pierre.

The election scheduled for May 11 would not take place. The report issued by the investigating committee on May 5, failed to realize the potential danger of a large V-shaped notch cut through cliffs surrounding the summit crater. The notch was like a colossal gun sight pointing directly at St. Pierre four miles below. At about 7:50 a.m. on May 8, the volcano erupted with a deafening roar. A large black cloud composed of superheated gas, ash and rock rolled headlong down the south flank of Mt. Pelée at more than 100 miles per hour, its path directed by the V-shaped notch at the summit. In less than one minute it struck St. Pierre with hurricane force. The blast was powerful enough to carry a three-ton statue sixteen meters from its mount. One-meter-thick masonary walls were blown into rubble and support girders were mangled into twisted strands of metal. The searing heat of the cloud ignited huge bonfires. Thousands of barrels of rum stored in the city's warehouses exploded, sending rivers of the flaming liquid through the streets and into the sea. The cloud continued to advanced over the harbor where it destroyed at least twenty ships anchored offshore. The hurricane force of the blast capsized the steamship Grappler, and its scorching heat set ablaze the American sailing ship Roraima, killing most of her passengers and crew. The Roraima had the misfortune of arriving only a few hours before the eruption. Those on on board could only watch in horror as the cloud descended on them after annihilating the city of St. Pierre. Of the ~28,000 people in St. Pierre, there were only two known survivors.

The dynamic cloud of hot gases and incandescent solid particles that destroyed St. Pierre was a pyroclastic flow, a feature that was unknown to science at the time. Subsequent examples observed on Mt. Pelée were described by French volcanologists as nuée ardentes, or glowing clouds.

There were only two survivors of the event.  The most famous being a husky 25-year-old roustabout named Louis-Auguste Cyparis, locally known simply as "Samson". In early April, Samson was put in jail for wounding one of his friends with a cutlass. Towards the end of his sentence, he escaped from a labouring job in town, danced all night, and then turned himself into the authorities the following morning. For this, he was sentenced to solitary confinement for a week in the prison's dungeon. On May 8, he was alone in his dungeon with only a small grated opening cut into the wall above the door. While waiting for his breakfast, his cell became dark and he was overcome by intense gusts of hot air mixed with ash that had entered through the grated opening. He held his breathe while experiencing intense pain. After a few moments, the heat subsided. He was severally burned, but managed to survive for four days before he was rescued by people exploring the ruins of St. Pierre. After he recovered, he received a pardon and eventually joined the Barnum & Bailey Circus, where he toured the world billed as the "Lone Survivor of St. Pierre."