Kamis, 20 Januari 2011

sejarah merapi

HISTORY OF GEOLOGY
The results show the history of the formation of Merapi stratigraphy is very complex. Wirakusumah (1989) Geology Merapi divides into 2 major groups namely Merapi Merapi Young and Old. Subsequent research (Berthomier, 1990; Newhall & Bronto, 1995; Newhall et.al, 2000) found the stratigraphic units at Merapi are more detailed. According Berthommier, 1990 based on stratigraphic studies, the history of Merapi can be divided into 4 parts:
PRE MERAPI (+ 400,000 years ago)
Referred to as Mount Aunt with andesitic-basaltic magma ± 700,000 years old located on the eastern slope of Merapi including Boyolali district. Volcanic rocks are andesitic-basaltic aunt but does not contain orthopyroxen. Aunt peak has an altitude of about 2050 m above sea level with flat distance between the peak and the peak of Merapi Bibi is now about 2.5 km. Because of the very old age Mount Aunt experiencing strong alteration so hard to find fresh rock specimens. MERAPI OLD (60000-8000 years ago)
At this time begin to birth, known as the Mount Merapi, which is the initial phase of its formation with immature cone. Initially in the form of basaltic lava extrusion that forms Mount Turgo and Plawangan about 40,000 years old. Product activity consists of rocks with basaltic andesite composition of awanpanas, brecciation of lava and lava. MERAPI MID (8000 - 2000 years ago)
Occurred some molten lava that make up the hill Batulawang andesitic and Gajahmungkur, which is currently visible on the northern slopes of Merapi. Rock composed of lava flows, lava and hot clouds brecciation. Merapi activity is characterized by effusive eruptions (melt) and explosive. Also estimated that an explosive eruption with "de ¬ bris-avalanche" to the west that left morphology with a long horse shoe-7 km, 1-2 km wide with a few hills on the western slope. In this period Pasarbubar formed crater.


NEW MERAPI (2000 years ago - present)
In the crater of Merapi summit cone formed Pasarbubar currently known as Mount Anyar which is currently a central activity of Merapi. The basement of Old Merapi Merapi may be old. While Merapi is now about 2000 years old. Major eruption of Merapi occurred in the past that the distribution of the material being covered Sambisari located ± 23 km south of Merapi. Stratigraphic studies conducted by Andreastuti (1999) have shown that several major eruption, the eruption index (VEI) of 4, Plinian type, have occurred in the past. The last major eruption with a fairly broad distribution of tephra produced Selokopo which occurred around about 500 years ago. Smaller explosive eruptions observed estimated 250 years ago which resulted Pasarbubar tephra. Schematic cross-section according to the geological history of Merapi Berthommier, 1990 (picture right). Map showing the distribution of sediment awanpanas Merapi 1911-2006. Only the eastern slope that is free from the direction of flow awapanas in this period.

 
HISTORY eruption
Mount Merapi eruption type can be categorized as a type Vulkanian weak. Other types such as Plinian (eg eruption of Vesuvius in 79) is a type of power vulkanian with a very strong explosion. Merapi eruption yet not so explosive pyroclastic flow is almost always occur in each eruption. The visual activity of Merapi eruption seen through a long process since it began with the formation of lava domes, lava and incandescent awanpanas (pyroclastic flow).
Including Merapi volcano erupts frequently. Until June 2006, has recorded eruption was 83 times the incident. On average interval Merapi eruption occurred between 2-5 years (short period), while the medium over that time period every 5-7 years. Merapi has experienced the longest period of rest for> 30 years, especially early in its existence as a volcano. Entering the 16th century recorded the activities of Merapi began well enough. At this time seen that the longest break ever achieved for 71 years when the gap between in 1587 until the year 1658.


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