seismically monitored regions of the World with stations on the Hawaiian islands,
in French Polynesia, and on the west coast of the USA, while the other oceans such
as the south Atlantic, the Arctic and the Indian oceans, are relatively deprived of
seismic monitoring and warning systems.
Today about 10 % of the Earth’s population lives near the 1,500 active subaerial volcanic edifices. This is due to the nature of the fertile soil, which is
excellent for growing crops. In 1983, prior to the eruption of the Colo Volcano on
Una-Una Island of the Sulawesi province North of Java (Indonesia), an Earthquake
swarm followed by a volcanic eruption occurred on July 14–18, 1983. Because
Indonesian geologists had gained experience from past eruptions of a similar type
of volcano, they recommended that their government evacuate 7,000 people from
the Island, which they did, and thereby saved their lives. A devastating tsunami
and pyroclastic flow destroyed the island completely (Katili and Sudradjat 1984).
In 1980, when the Mount St. Helens volcano erupted in Washington State, it was
known that this volcano had been active about every 100–140 years since
1400 A.D. (Fisher et al. 1998).
The composition of the magma that feeds an edifice will also determine the type
of eruption. The most dangerous for humans are the so-called pyroclastic
(explosive) types of eruption that carry a cloud of broken fragments and gas. These
flows move faster than wind-driven hurricanes and can reach temperatures as hot
as 800 °C. Lava will flow as quickly as 100 km an hour and over distances of more
than 100 km away from the source. Such types of volcanoes can damage cars, bury
towns and burn entire forests. It was this type of pyroclastic eruption from Mont
Pelée which destroyed the city of St. Pierre in Martinique in 1902, causing 30,000
deaths in only a few minutes. New methods of detection, such as satellite images
and local observatories on or near volcanoes and which have been used since the
end of the twentieth century, have enabled increased understanding concerning
catastrophic volcanic eruptions. (Fisher et al. 1998).
Looking at the examples of the Mt. St. Helen’s eruption in 1980, Mt. Unzen in
Japan in 1991, and Mt. Pinatubo in the Philippines in 1991, we know that these
volcanoes’ activities were detected and the evolution of their volcanic clouds was
closely monitored. In other areas, volcanoes are still killers. For example, the
eruption of Nevado de Ruiz in Columbia in 1985 was more disastrous than what
happened after the explosion of Mont Pelée 80 years earlier. A glacier capping the
volcano at an altitude of 5400 m high collapsed and the subsequent mixture of
muddy water and volcanic debris swept down the slopes of the volcano causing a
devastating mud flow that killed 25,000 people 5000 m below the summit of the
edifice.
The Pinatubo volcano, after being inactive for more than 500 years, suddenly
came alive on June 15, 1991. The day before, Philippine officials ordered the
population of more than eighty thousand people to evacuate the surroundings
(Sigurdsson et al. 2000). The explosion of the Pinatubo volcano deposited voluminous pyroclastic flows extending up to 16 km from the vent and distributed over
an area of more than 400 km
2 . Only three hundred people were killed by this
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5 Earth’s Mantle Melting and Volcanism
in French Polynesia, and on the west coast of the USA, while the other oceans such
as the south Atlantic, the Arctic and the Indian oceans, are relatively deprived of
seismic monitoring and warning systems.
Today about 10 % of the Earth’s population lives near the 1,500 active subaerial volcanic edifices. This is due to the nature of the fertile soil, which is
excellent for growing crops. In 1983, prior to the eruption of the Colo Volcano on
Una-Una Island of the Sulawesi province North of Java (Indonesia), an Earthquake
swarm followed by a volcanic eruption occurred on July 14–18, 1983. Because
Indonesian geologists had gained experience from past eruptions of a similar type
of volcano, they recommended that their government evacuate 7,000 people from
the Island, which they did, and thereby saved their lives. A devastating tsunami
and pyroclastic flow destroyed the island completely (Katili and Sudradjat 1984).
In 1980, when the Mount St. Helens volcano erupted in Washington State, it was
known that this volcano had been active about every 100–140 years since
1400 A.D. (Fisher et al. 1998).
The composition of the magma that feeds an edifice will also determine the type
of eruption. The most dangerous for humans are the so-called pyroclastic
(explosive) types of eruption that carry a cloud of broken fragments and gas. These
flows move faster than wind-driven hurricanes and can reach temperatures as hot
as 800 °C. Lava will flow as quickly as 100 km an hour and over distances of more
than 100 km away from the source. Such types of volcanoes can damage cars, bury
towns and burn entire forests. It was this type of pyroclastic eruption from Mont
Pelée which destroyed the city of St. Pierre in Martinique in 1902, causing 30,000
deaths in only a few minutes. New methods of detection, such as satellite images
and local observatories on or near volcanoes and which have been used since the
end of the twentieth century, have enabled increased understanding concerning
catastrophic volcanic eruptions. (Fisher et al. 1998).
Looking at the examples of the Mt. St. Helen’s eruption in 1980, Mt. Unzen in
Japan in 1991, and Mt. Pinatubo in the Philippines in 1991, we know that these
volcanoes’ activities were detected and the evolution of their volcanic clouds was
closely monitored. In other areas, volcanoes are still killers. For example, the
eruption of Nevado de Ruiz in Columbia in 1985 was more disastrous than what
happened after the explosion of Mont Pelée 80 years earlier. A glacier capping the
volcano at an altitude of 5400 m high collapsed and the subsequent mixture of
muddy water and volcanic debris swept down the slopes of the volcano causing a
devastating mud flow that killed 25,000 people 5000 m below the summit of the
edifice.
The Pinatubo volcano, after being inactive for more than 500 years, suddenly
came alive on June 15, 1991. The day before, Philippine officials ordered the
population of more than eighty thousand people to evacuate the surroundings
(Sigurdsson et al. 2000). The explosion of the Pinatubo volcano deposited voluminous pyroclastic flows extending up to 16 km from the vent and distributed over
an area of more than 400 km
2 . Only three hundred people were killed by this
136
5 Earth’s Mantle Melting and Volcanism