Jumat, 05 November 2010

Merapi Volcano

Central Java, Indonesia

7.54 S, 110.44 E
summit elevation 2911 m

Merapi volcano is one of the world's most active and dangerous volcanoes. It contains an active lava dome which regularly produces pyroclastic flows. Eruptions occur at intervals of 1-5 years and are of low gas pressure. Since magma is poor in gas, eruptions are usually less than VEI 3 in size.

Merapi is one of the most active volcanoes in Indonesia and has produced more pyroclastic flows than any other volcano in the world. It has been active for 10,000 years.

Most eruptions of Merapi involve a collapse of the lava dome creating pyroclastic flows which travel 6 to 7 km from the summit. Some awan panas have traveled as far as 13 km from the summit, such as the deposit generated during the 1969 eruption. Velocity of pyroclastic flows can reach up to 110 km/hour. A slow up flow of andesitic magma leads to an extrusion of viscous magma, which accumulate and construct a dome in the crater.

Violent Eruptions at Merapi volcano
There is evidence that the current low level of activity may be interrupted by larger explosive eruptions. Eruptions of Merapi volcano during the 7–19th centuries A.D. were more violent than the past hundred years, and produced explosion pyroclastic flows. Widespread pyroclastic flows and surges traveled up to 25 km down the flanks of Merapi.

Scientists predict that the quiet of the 20th century will be broken by a larger
explosive eruption within coming decades. (Scientific report published in 2000).

2010 Eruption
Merapi volcano was raised to level 3 alert (out of a maximum 4) due to inflation and volcanic earthquakes on 21st October 2010. Sand miners were asked to stop all activity, and people advised not to climb the volcano.
Merapi volcano erupted on 26th October 2010 killing 34 people.

2006 Eruptions
Seismic activity began increasing at Merapi volcano in March 2006, and 10,000 residents were prepared for evacuation. On 10th April people were banned from climbing the volcano. On 12th April the Alert Level was raided from 2 to 3. An 8 km exclusion zone was placed around the volcano. On 27th April nearly 2,000 villagers were evacuated from Sidorejo and Tegalmulyo villages around Merapi volcano. On 13th May, the Alert Level was raised to the highest level 4, and about 4,500 people living near the volcano were evacuated. On 15th May pyroclastic flows traveled up to 4 km west. By 16th May, more than 22,000 people had been evacuated. On 8th June, the lava-dome growth rate at Merapi was an estimated 100,000 cubic meters per day, with an estimated volume of 4 million cubic meters. Pyroclastic flows and rockfalls decreased in frequency and intensity after 28th June 2006.

2006 Earthquakes
On 27th May 2006 a magnitude 6.3 earthquake killed about 5,400 people produced in a three-fold increase in activity at Merapi volcano. On 17th July 2006 a magnitude 7.7 earthquake hit 50 km south of Merapi volcano. The earthquake was the result of thrust-faulting on the boundary between the Australian and Sunda tectonic plates. The earthquake produced an 8 m high tsunami which hit the southern coast of Java. This event was classified as a tsunami earthquake, because of the low earthquake magnitude compared to the tsunami size. The earthquake caused 5,750 deaths, 38,560 injuries, and up to 600,000 people displaced in the Bantul-Yogyakarta area.

2001 Eruption
A major eruption began at Merapi volcano on 10th February 2001. A 30-minute-long pyroclastic flow occurred at 0200 hr. At 0330 hr there was a collapse of the 1998 lava dome which ejected ash 5 km above the summit and produced a pyroclastic flows that extended 7 km in the direction of the Sat River.

1998 Eruptions
Activity at Merapi volcano began increasing in July 1998. On 11th July 37 nuées ardentes occurred between midnight and 0500 hr. Between 11-19 July, 128 nuées ardentes occurred, including a strong pyroclastic ash and block flow at 1500 on 19th July.

1994 Eruptions
On 22nd November 1994, a large number of dome-collapse nuees ardentes were generated over a period of several hours at Merapi volcano. The nuees ardentes descended mainly the Boyong valley and the Bedog valley, a tributary of the Krasak-Kecil valley. This was in contrast to the 1984 and 1992 flows which traveled exclusively towards the southwest and west.

1986-87 Eruptions
Lava dome formation at Merapi volcano in 1986-87 was the largest since 1973.

1968 Eruptions
At the end of May 1968 a lava tongue had extended 875 m and was the result of new lava done extrusion after the 1967 collapse. The number of avalanches from the lava tongue were 1432 in June, 1370 July, 329 August, and 12 in September. Renewed activity began at Merapi volcano in October 1968 with an increasing number of lava avalanches.

1967 Eruptions
A lava dome extruded in April 1967 at the upper Batang River on the SW slope of Merapi volcano. The dome collapsed in October 1967.

1822 Lahar
A hot lahar at Merapi volcano on 28th December 1822 destroyed 4 villages with 100 casualties.
Merapi Volcano Eruptions

2010, 2007, 2006, 2001-02, 1992-98, 1972-90, 1971, 1967-69, 1961, 1953-58, 1948-49, 1944-45, 1942-43, 1939-40, 1933-35, 1930-31, 1924, 1923, 1922, 1920-21, 1918, 1915, 1909-13, 1908, 1906-07, 1905, 1902-04, 1902, 1897, 1894, 1893, 1891, 1889, 1888, ?1885, 1883-84, 1878-79, 1872-73, 1872, 1869, 1865-67, 1862-64, ?1854, 1849, ?1848, 1846-47, 1846, 1840, 1837-38, 1832-35, 1828, 1822-23, 1820-22, 1812-13, 1810, 1807, 1797, 1786, 1755, 1752, 1745, 1678, 1677, 1672, 1663, 1658, 1587, 1584, 1560, 1554, 1548, 7630 BC.

* Volcanoes of Indonesia.

source : http://www.volcanolive.com/merapi.html

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