Saturday, November 20, 2010

The most catastrophic volcanic eruptions by Catastrophe Monitor

A volcano is a landform (usually a mountain) where molten rock erupts through the surface of the planet. In simple terms a volcano is a mountain that opens downward to a pool of molten rock (magma) below the surface of the earth. It is a hole in the Earth from which molten rock and gas erupt.

The name "volcano" has its origin from the name of Vulcan, a god of fire in Roman mythology. As pressure in the molten rock builds up it needs to escape somewhere. So it forces its way up "fissures" which are narrow cracks in the earths crust. Once the magma erupts through the earth's surface it's called lava.

10. Mount Kelut (May 19, 1919)

Death Toll = 5,115

Kelut is a volcano located in East Java on Java in Indonesia. Like many Indonesian volcanoes and others on the Pacific Ring of Fire, Kelud is known for large explosive eruptions throughout its history. More than 30 eruptions have occurred since 1000 A.D.

On May 19, 1919, an eruption at Kelud killed an estimated 5,000 people, mostly through hot mudflows (also known as "lahars"). More recent eruptions in 1951, 1966, and 1990 have altogether killed another 250 people. Following the 1966 eruption, the Ampera Tunnel was built on the southwestern side of the crater to drain the crater lake and thus reduce the lahar hazard.

09. Santa Maria (October 24, 1902)

Death Toll = 6,000

Santa María Volcano is a large active volcano in the Western Highlands of Guatemala, close to the city of Quetzaltenango. Prior to the Spanish Conquest it was called Gagxanul in the local K'iche' language. Its eruption in 1902 (VEI 6) was one of the four largest eruptions of the 20th century, after the 1912 Novarupta and 1991 Pinatubo eruptions. It is also one of the five biggest eruptions of the past 200 (and probably 300) years.

The first eruption of Santa María in the recorded history occurred in October 1902. Before 1902 the volcano had been dormant for at least 500 years and possibly several thousand years, but its awakening was clearly indicated by a seismic swarm in the region starting in January 1902, which included a major earthquake in April 1902. The eruption began on 24 October, and the largest explosions occurred over the following two days, ejecting an estimated 5.5 cubic kilometres (1.3 cu mi) of magma. The eruption was one of the largest of the 20th century, only slightly less in magnitude to that of Mount Pinatubo in 1991. The eruption had a VEI of 6, thus being 'Colossal'.

08. Laki (June 8, 1783)

Death Toll = 9,350

Laki or Lakagígar (Craters of Laki) is a volcanic fissure situated in the south of Iceland, not far from the canyon of Eldgjá and the small village Kirkjubæjarklaustur, in South-East Iceland. Lakagígar is the correct name as the Laki mountain itself did not erupt, but fissures opened up on each side of it. Lakagígar is part of a volcanic system, centering on the Grímsvötn volcano and including the Thórdarhyrna volcano. It lies between the glaciers of Mýrdalsjökull and Vatnajökull, in an area of fissures which run in a south-west to north-east direction.

On 8 June 1783, a fissure with 130 craters opened with phreatomagmatic explosions because of the groundwater interacting with the rising basalt magma. Over a few days the eruptions became less explosive, Strombolian, and later Hawaiian in character, with high rates of lava effusion. This event is rated as VEI 6 on the Volcanic Explosivity Index, but the eight month emission of sulfuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium.

07. Mount Kelut again (November 1586)

Death Toll = 10,000

Again, Mount Kelut is on the list of the most catastrophic volcano eruptions. Back in 1586, Kelut erupted and killed aproximaly 10k people.

06. Mount Unzen (1792)

Death Toll = 15,000

Mount Unzen (Unzendake) is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki Prefecture, on the island of Kyūshū, Japan's southernmost main island.

In 1792, the collapse of one of its several lava domes triggered a tsunami that killed about 15,000 people in Japan's worst-ever volcanic-related disaster. The volcano was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow that killed 43 people, including three volcanologists.

Unzen's deadliest eruption occurred in 1792, with a large dacitic lava flow coming from Fugendake. The east flank of the Mayuyama dome collapsed unexpectedly following a post-eruption earthquake, creating an avalanche and tsunami that killed an estimated 15,000 people. This remains Japan's worst-ever volcanic-related disaster.

05. Nevado del Ruiz (November 13, 1985)

Death Toll = 23,000

Nevado del Ruiz, also known as El Mesa de Herveo or Kumanday, is the northernmost volcano of the Andean Volcanic Belt, lying about 129 kilometers (80 mi) west of Bogotá in the Tolima Department of Colombia. It is a stratovolcano, composed of many layers of lava alternating with hardened volcanic ash and other pyroclastic rocks. Nevado del Ruiz has been active for about two million years, since the early Pleistocene or late Pliocene epoch, with three major eruptive periods. The current volcanic cone formed during the "present" eruptive period, which began 150 thousand years ago.

Beginning November 1984, geologists observed an increasing level of seismic activity near Nevado del Ruiz. Other signs of a forthcoming eruption included increased fumarole activity, deposition of sulfur on the summit of the volcano, and small phreatic eruptions. In the latter, hot magma came in contact with water, resulting in explosions as the water was almost instantly turned into steam. The most notable of these events was an ash ejection on September 11, 1985. The activity of the volcano decreased in October 1985. The most likely explanation of the events is that new magma rose into the volcanic edifice before September 1985.

At 9:09 pm, on November 13, 1985, Nevado del Ruiz erupted, ejecting dacitic tephra more than 30 kilometres (19 mi) into the atmosphere. The total mass of the erupted material (including magma) was 35 million tonnes - only 3% of the amount that erupted from Mount St. Helens in 1980. The eruption reached a value of 3 on the Volcanic Explosivity Index. The mass of the ejected sulfur dioxide was about 700,000 tonnes, or about 2% of the mass of the erupted solid material, making the eruption atypically sulfur-rich.

The eruption produced pyroclastic flows that melted summit glaciers and snow, generating four thick lahars that raced down river valleys on the volcano's flanks. It also destroyed a small lake that was observed in Arenas crater several months before the eruption. Water in such volcanic lakes tends to be extremely salty and contain dissolved volcanic gases. The lake's hot, acidic water significantly accelerated the melting of the ice; this effect was confirmed by the large amounts of sulfates and chlorides found in the lahar flow.

04. Mount Pelee (May 7 or May 8, 1902)

Death Toll = 29,000

Mount Pelée is an active volcano on the northern tip of the French overseas department of Martinique in the Lesser Antilles island arc of the Caribbean. It is among the deadliest stratovolcanoes on Earth. Its volcanic cone is composed of layers of volcanic ash and hardened lava.

The volcano is now famous for its eruption in 1902 and the destruction that resulted, now dubbed the worst volcanic disaster of the 20th century. The eruption killed about 30,121 people. Most deaths were caused by pyroclastic flows and occurred in the city of Saint-Pierre, which was, at that time, the largest city in Martinique.

On May 8, 1902, Ascension Day, a volcanic eruption destroyed the town of Saint-Pierre, about 6.4 kilometres (4.0 mi) south of the summit.

In the morning, people were observing the fireworks the mountain was displaying. The night shift telegraph operator was sending the reports of the volcano's activity, to the operator at Fort-de-France, claiming no significant new developments; his last transmission was "Allez", handing over the line to the remote operator. It was 7:52; the next second, the telegraph line went dead. A cable repair ship had the city in direct view; the upper mountainside ripped open and a dense black cloud shot out horizontally. A second black cloud rolled upwards, forming a gigantic mushroom cloud and darkening the sky in a 50-mile (80 km) radius. The initial speed of both clouds was later calculated to be over 670 kilometres (420 mi) per hour.

A rush of wind followed, this time towards the mountain. Then came a half-hour downpour of muddy rain mixed with ashes. For the next several hours, all communication with the city was severed. Nobody knew what was happening, nor who had authority over the island, as the governor was unreachable and his status unknown. Some survivors were picked from the sea, mostly badly burned sailors who had been blown into the sea by the blast and then clung for hours to floating debris.

A warship approached the shore at about 12:30, but the intense heat prevented it from landing until about 3 PM. The city burned for several more days.

The area devastated by the pyroclastic cloud covered about 8 square miles (21 km2), with the city of Saint-Pierre taking its brunt.

03. Mount Vesuvius (August 24, 79 AD)

Death Toll = 33,000

 Mount Vesuvius (Italian: Monte Vesuvio, Latin: Mons Vesuvius) is a stratovolcano on the Bay of Naples, Italy, about 9 kilometres (5.6 mi) east of Naples and a short distance from the shore. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting. The two other major active volcanoes in Italy, Etna and Stromboli, are located on islands.

Mount Vesuvius is best known for its eruption in AD 79 that led to the destruction of the Roman cities of Pompeii and Herculaneum. They were never rebuilt, although surviving townspeople and probably looters did undertake extensive salvage work after the destructions. The towns' locations were eventually forgotten until their accidental rediscovery in the 18th century.

The AD 79 eruption was preceded by a powerful earthquake seventeen years beforehand on 5 February, 62, which caused widespread destruction around the Bay of Naples, and particularly to Pompeii. Some of the damage had still not been repaired when the volcano erupted. The deaths of 600 sheep from "tainted air" in the vicinity of Pompeii reported by Seneca the Younger leads Sigurdsson to compare them to similar deaths of sheep in Iceland from pools of volcanic Carbon Dioxide and to speculate that the earthquake of 62 was related to new activity by Vesuvius.

02. Krakatoa (August 26-27, 1883)

Death Toll = 36,000

Krakatoa (Indonesian: Krakatau), also spelled Cracatoa or Krakatau, is a volcanic island made of a'a lava in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The name is used for the island group, the main island (also called Rakata), and the volcano as a whole. The island exploded in 1883, killing approximately 40,000 people, although some estimates put the death toll much higher. The explosion is still considered to be the loudest sound ever heard in modern history, with reports of it being heard nearly 3000 miles from its point of origin. The shock wave from the explosion was recorded on barographs around the globe.

On August 27, a series of four huge explosions almost entirely destroyed the island. The explosions were so violent that they were heard 3,500 km (2,200 mi) away in Perth, Western Australia and the island of Rodrigues near Mauritius, 4,800 km (3,000 mi) away. The pressure wave from the final explosion was recorded on barographs around the world, which continued to register it up to 5 days after the explosion. The recordings show that the shockwave from the final explosion reverberated around the globe 7 times in total. Ash was propelled to a height of 80 km (50 mi).

Average global temperatures fell by as much as 1.2 degrees Celsius in the year following the eruption. Weather patterns continued to be chaotic for years and temperatures did not return to normal until 1888.

01. Mount Tambora (April 10, 1815)

Death Toll = 92,000

Mount Tambora (or Tamboro) is an active stratovolcano, also known as a composite volcano, on the island of Sumbawa, Indonesia.

The 1815 eruption is rated 7 on the Volcanic Explosivity Index, the only such eruption since the Lake Taupo eruption in about 180 AD. With an estimated ejecta volume of 160 cubic kilometers, Tambora's 1815 outburst was the largest volcanic eruption in recorded history. The explosion was heard on Sumatra island (more than 2,000 km (1,200 mi) away). Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, Java and Maluku islands. Most deaths from the eruption were from starvation and disease, as the eruptive fallout ruined agricultural productivity in the local region. The death toll was at least 71,000 people (the most deadly eruption in recorded history), of whom 11,000-12,000 were killed directly by the eruption; the often-cited figure of 92,000 people killed is believed to be overestimated. The eruption created global climate anomalies that included the phenomenon known as "volcanic winter": 1816 became known as the "Year Without a Summer" because of the effect on North American and European weather. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in the worst famine of the 19th century.

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