"On the afternoon of 25 October 2010 Mount Merapi erupted lava from its southern and southeastern slopes."Merapi, Gunung Merapi (literally Mountain of Fire in Indonesian/Javanese), lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. With summit elevation about 3000 m, it is one of Indonesia's most active volcanoes in Indonesia. It has erupted regularly since 1548. It is very close to the city of Yogyakarta, and thousands of people live on the flanks of the volcano, with villages as high as 1700 m above sea level.
Merapi is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi volcano beginning during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the volcano's western-to-southern flanks and caused many fatalities during historical time. The volcano is the object of extensive monitoring efforts by the Merapi Volcano Observatory.
Merapi has the unfortunate distinction of producing more nuee ardentes than any other volcano on Earth. The nuee ardentes result from collapse of the lava dome at the summit. Of the 67 historic eruptions 32 have had nuee ardentes associated with them. Eleven of these eruptions resulted in fatalities. Merapi is closely monitored by the Volcanological Survey of Indonesia. Shortly before this photograph was taken Merapi was generating up to 40 nuee ardentes per day.
The name Merapi could loosely translated as 'Mountain of Fire' from the Javanese combined words; Meru means "mountain" and api means "fire". Smoke can be seen emerging from the mountaintop at least 300 days a year, and several eruptions have caused fatalities. Hot gas from a large explosion killed 64 people on November 22 in 1994, mostly in the town of Muntilan, west of the volcano[citation needed]. Another large eruption occurred in 2006, shortly before the Yogyakarta earthquake. In light of the hazards that Merapi poses to populated areas, it has been designated as one of the Decade Volcanoes.
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Culture
Merapi continues to hold particular significance for the Javanese: it is one of four places where officials from the royal palaces of Yogyakarta and Solo make annual offerings to placate the ancient Javanese spirits. To keep the volcano quiet, the Javanese regularly bring offerings on the anniversary of the sultan of Yogyakarta's coronation. For Yogyakarta Sultanate, Merapi holds significant cosmological symbolism, because it is forming a sacred north-south axis line between Merapi peak and Southern Ocean (Indian Ocean). The sacred axis is signify by Merapi peak in the north, the Tugu monument near train station, the axis runs along Malioboro street to Northern Alun-alun (square) across Keraton Yogyakarta (sultan palace), Southern Alun-alun, all the way to Bantul and finally reach Southern Ocean.
MonitoringMerapi is a basaltic to basaltic-andesite stratovolcano with a summit crater containing an unstable lava dome. Merapi is Indonesia's most active volcano and well known for partial collapse of lava domes and the generation of pyroclastic flows. Pyroclastic flows can travel as far as 8 miles (13 km) from the summit and reach speeds of 70 mph (110 km/hr). Pyroclastic flow deposits can be remobilized as lahars. Direct observations of Merapi have been recorded since 1888. Recent study of tephra deposits on the flanks of the volcano found 27 marker beds that reveal Merapi's past history. The volcano has had numerous moderate to large (1 million cubic m) eruptions. These eruptions typically begin with pyroclastic flows and are followed by widespread pyroclastic air fall. Plinian to subplinian eruptions are common. These older deposits indicate that Merapi is capable of eruption styles very different from those currently observed.
Mount Merapi is the site of a very active volcano monitoring program. Seismic monitoring began in 1924, with some of the volcano monitoring stations lasting until the present. The Babadan (northwest location), Selo (in the saddle between Merbabu and Merapi), and Plawangan monitoring stations have been updated with equipment over the decades since establishment. During the 1950s and early 1960s some of the stations were starved of equipment and funds, but after the 1970s considerable improvement occurred with the supply of new equipment. Some of the pre-1930 observation posts were destroyed by the 1930 eruption, and newer posts were re-located.
Similarly after the 1994 eruption, the Plawangan post and equipment were moved into Kaliurang as a response to the threat of danger to the volcanological personnel at the higher point. The eruption of 1930 was found to have been preceded by a large earthquake swarm. The network of 8 seismographs currently around the volcano allow volcanologists to accurately pinpoint the hypocentres of tremors and quakes. A zone in which no quakes originate is found about 1.5 km below the summit, and is thought to be the location of the magma reservoir which feeds the eruptions. Other measurements taken on the volcano include magnetic measurements and tilt measurements.
Small changes in the local magnetic field have been found to coincide with eruptions, and tilt measurements reveal the inflation of the volcano caused when the magma chambers beneath it is filling up. Lahars (a type of mudflow of pyroclastic material and water) are an important hazard on the mountain, and are caused by rain remobilizing pyroclastic flow deposits. Lahars can be detected seismically, as they cause a high-frequency seismic signal. Observations have found that about 50 mm of rain per hour is the threshold above which lahars are often generated.
Geological histories
Merapi is the youngest in a group of volcanoes in southern Java. It is situated at a subduction zone, where the Indo-Australian Plate is sliding beneath the Eurasian Plate. It is one of at least 129 active volcanoes in Indonesia, part of the Pacific Ring of Fire – a section of fault lines stretching from the Western Hemisphere through Japan and South East Asia. Stratigraphic analysis reveals that eruptions in the Merapi area began about 400,000 years ago, and from then until about 10,073 years ago, eruptions were typically effusive, and the outflowing lava emitted was basaltic.
Since then, eruptions have become more explosive, with viscous andesitic lavas often generating lava domes. Dome collapse has often generated pyroclastic flows, and larger explosions, which have resulted in eruption columns, have also generated pyroclastic flows through column collapse. There has been no late eruption. Typically, small eruptions occur every two to three years, and larger ones every 10–15 years or so. Notable eruptions, often causing many deaths, have occurred in 1006, 1786, 1822, 1872, and 1930—when thirteen villages were destroyed and 1400 people killed by pyroclastic flows. A very large eruption in 1006 is claimed to have covered all of central Java with ash. The volcanic devastation is claimed to have led to the collapse of the Hindu Kingdom of Mataram, however there is insufficient evidence from that era for this to be substantiated.
In April 2006, increased seismicity at more regular intervals and a detected bulge in the volcano's cone indicated that fresh eruptions were imminent. Authorities put the volcano's neighboring villages on high alert and local residents prepared for a likely evacuation. On April 19 smoke from the crater reached a height of 400 meters, compared to 75 metres the previous day. On April 23, after nine surface tremors and some 156 multifaced quakes signalled movements of magma, some 600 elderly and infant residents of the slopes were evacuated.[5]
By early May, active lava flows had begun. On May 11, with lava flow beginning to be constant, some 17,000 people were ordered to be evacuated from the area and on May 13, Indonesian authorities raised the alert status to the highest level, ordering the immediate evacuation of all residents on the mountain. Many villagers defied the dangers posed by the volcano and returned to their villages, fearing that their livestock and crops would be vulnerable to theft. Activity calmed by the middle of May. On May 27, a 5.6 magnitude earthquake struck roughly 30 miles southwest of Merapi, killing at least 5,000 and leaving at least 200,000 people homeless in the Yogyakarta region, heightening fears that Merapi would "blow". The quake did not appear to be a long-period oscillation, a seismic disturbance class that is increasingly associated with major volcanic eruptions. A further 11,000 villagers were evacuated on June 6 as lava and superheated clouds of gas poured repeatedly down its upper slopes towards Kaliadem, a location that was located southeast of Mt. Merapi. The pyroclastic flows are known locally as "wedhus gembel" (Javanese for "shaggy goat"). There were two fatalities as the result of the eruption.On 25 October 2010 the Indonesian government raised the alert for Mount Merapi to its highest level and warned villagers in threatened areas to move to safer ground. People living within a 10km (6 mile) zone were told to evacuate. Officials said about 500 volcanic earthquakes had been recorded on the mountain over the weekend of 23-24 October, and that the magma had risen to about a kilometre below the surface due to the seismic activity. On the afternoon of 25 October 2010 Mount Merapi erupted lava from its southern and southeastern slopes.
source:
http://en.wikipedia.org
http://volcano.oregonstate.edu
http://www.volcano.si.edu
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