SOME VOLCANIC ERUPTIONS AND DISTRIBUTION OF VOLCANOES IN THE WORLD
In the history of mankind perhaps the most disastrous eruptions were those of Mt. Vesuvius, Mt. Krakatoa and Mt. Pelee.
Mt. Vesuvius, standing 1200m (4000 feet) above the Bay of Naples, erupted violently on 24 August A.D. 79, taking the people who lived around it by complete surprise. White-hot lava flowed from parasitic cones. In the midst of a thundering explosion, the highly gaseous magma escaped as gigantic luminous clouds in cauliflower form and shot up to great heights before it fell to earth as pyroclasts and ashes. The city of Pompeii, located to the south-west, was buried beneath six metres (20 feet) of volcanic ashes which were later cemented by the torrential downpours of heavy rain that accompanied the violent eruption. In a similar way, the city of Herculaneum on the west was completely overwhelmed by a mudflow of ashes and cinders almost 15 m (50 feet) thick, washed down by torrential rain from the slopes of Vesuvius. Almost the entire population of the two cities was buried alive.
After this, minor eruptions occurred from time to time but the fertility of the solidified volcanic ashes tempted many farmers to begin anew on the slopes of Vesuvius. Then came the catastrophic eruption of December 1631 when an avalanche comprising red hot volcanic debris, pasty lava and highly energized gases ruined fifteen towns and killed 4000 inhabitants. The ashes that descended on Naples were estimated to be one-third of a metre (a foot) thick.
The greatest volcanic explosion known to man is perhaps that of Mt. Krakatoa in August 1883.
Krakatoa is a small volcanic island in the Sunda Straits, midway between Java and Sumatra. Dense black clouds of ashes shot 30-80 km (2050 miles) high and were brought down as mud by the torrential rain which fell over the adjacent islands. So much magma was ejected from the underlying reservoir that two-thirds of the island collapsed and disappeared, forming a huge submarine caldera. The explosion could be heard in Australia, almost 4800 km (300 miles) away. The fine dust that was thrown into the upper part of the atmosphere travelled several times around the world, causing brilliant sunsets and glowing sky in many parts of the globe. Though Krakatoa itself was not inhabited and nobody was killed by the lava flows, the vibration set up enormous waves over 30 m (100 feet) high which drowned 36 000 people in the coastal districts of Indonesia.
After remaining dormant for almost half a century, an eruption in 1927 pushed up a cinder cone fron the submarine floor, culminating in a summit of 66 m (220 feet) above sea-level by 1952. This new volcanic island was named Anak Krakatoa, meaning ‘the child of Mt. Krakatoa’.
The eruption of Mt. Pelee in the West Indies in May 1902 was the most catastrophic of modern times. The volcano erupted white-hot lava and superheated steam which swept down the slope at an amazing speed as a nulee ardente (glowing avalanche). St. Pierre, the capital of Martinique, lying on the path of the lava, was completely destroyed within minutes. Its entire population of 30 000, except two of them, was killed almost instantly. Even the sea was boiling and all the ships in the harbour were wrecked.
The ejection of volcanic materials continued for several months until a vertical spine rose from the crater, almost 300 m (1000 feet) high by the middle of 1903. The spine was formed by the pasty lava, partially solidified in the neck of the volcano. Part of the spine, however, crumbled under continual weathering as well as internal forces.
The Distribution of Volcanoes World
Volcanoes are located in a fairly clearly defined pattern around the world, closely related to regions that have been intensely folded or faulted. There are well over 500 active volcanoes and thousands of dormant and extinct ones. They occur along coastal mountain ranges, as offshore islands and in the midst of oceans, but there are few in the interiors of continents. The greatest concentration is probably that in the Circum-Pacific region. Popularly termed the ‘Pacific Ring of Fire’, which has been estimated to include two-thirds of the world’s volcanoes. The chain of volcanoes extends for almost 3200 km (2000 miles) from the Aleutian islands into Kamchatka, Japan, the Philippines, and Indonesia (Java and Sumatra in particular), south wards into the Pacific islands of Solomon, New Hebrides, Tonga and North Island, New Zealand. On the other side of the Pacific, the chain continues from the Andes to Central America (particularly Guatemala, Costa Rica and Nicaragua), Mexico and right up to Alaska. It is said that there are almost 100 active volcanoes in the Philippines, 40 in the Andes, 35 in Japan and more than 70 in Indonesia.
In contrast, the Atlantic coasts have comparatively few active volcanoes but many dormant or extinct volcanoes e.g. Madeira, Ascension, St. Helena, Cape Verde Islands and Canary Islands, but those of Iceland and the Azores are active. Volcanoes of the Mediterranean region are mainly associated with the Alpine folds e.g. Vesuvius, Etna, Stromboli, Vulcano and those of the Aegean islands. A few continue into Asia Minor (Mt. Ararat and Mt. Elbruz). The Himalayas have, surprisingly, no active volcano at all. In Africa, some volcanoes are found along the East African Rift Valley e.g. Mt. Kilimanjaro and Mt. Kenya, both probably extinct. The only active volcano of West Africa is Mt. Cameroon. There are some volcanic cones in Madagascar, but active eruption has not been known so far. The West Indian islands have experienced some violent explosions in recent times e.g. Mt. Pelee in Martinique and in St. Vincent further south. The Lesser Antilles are made up mainly of volcanic islands and some of them still bear signs of volcanic liveliness. Elsewhere in the interiors of continents-Asia, North America, Europe and Australia, active volcanoes are rare.
Geysers and Hot Springs
Geysers are fountains of hot water and superheated steam that may spout up to a height of 45 m (150 feet) from the earth beneath. The phenomena are associated with a thermal or volcanic region in which the water below is being heated beyond boiling point (100°C or 212°F ). The jet of water is usually emitted with an explosion and is often triggered off by gases seeping out of the heated rocks. Almost all the world’s geysers are confined to three major areas: Iceland, the Rotorua district of North Island, New Zealand, and Yellowstone Park of U.S.A. The world’s best known geyser is perhaps ‘Old Faithful’ in Yellowstone National Park, Wyoming, which erupts at regular intervals – every 63 minutes on the average.
Hot springs or thermal springs are more common, and may be found in any part of the earth where water sinks deep enough beneath the surface to be heated by the interior forces. The water rises to the surface without any explosion. Such springs contain dissolved minerals which may be of some medicinal value. Iceland has thousands of hot springs. Some of them have been harnessed to heat houses, swimming pools and for other domestic purposes. Hot springs and geysers have become tourist attractions e.g. in Japan and Hawaii, also Tambun, near Ipoh (Malaysia). The Wikki springs, which are an additional attraction to the Yankari Game Reserve near Bauchi (Nigeria), are warm springs with a constant temperature of 31°C (88°F). Another famous example of a warm spring in Nigeria is the Ikogosi warm spring in Ekiti State.