Mount Merapi lava: Do not panic, Acting Under Threat

The collapse of the lava dome Geger Boyo on June 14, 2006 caused a hot cloud Gendol River, south-southeast side of Mount Merapi, which claimed two lives. The incident also resulted in piles of 6 million cubic meters of sand, rock and ash. Special ash specifically referred to as pyroclastic deposits.
Since then, the crater G. Merapi is open in the direction S. Gendol. The next crater eruptions besides bringing the threat of hot clouds, also increasing the number of piles of material in S. Gendol. The rainy season, hot cloud of ash deposits will be the lava that may threaten the assets and livelihoods in the groove S. Gendol and S. Opaque.
"The number of materials in Gendol eruption since June 2006 about 10 million cubic meters," said Subandrio, head of section G. Merapi, Central Research and Development Engineering Kegunungapian (BPPTK), Directorate of Volcanology and Geological Hazard Mitigation, Ministry of Mines and Energy. He revealed it in his explanation about the context of threats to community-based preparedness training conducted by community and PSMB UPN "Veteran" Yogyakarta in Petung hamlets, villages Kepuharjo, Cangkringan, Sleman October 24, 2006.
"No need to panic, but must remain vigilant. That is, we must respond to the threat of lava that proportionately, "said Subandrio cautioned. Understandably, since September 2006 proclaimed would happen in S. lava Gendol which will flood the downstream regions. Other news is even mentioning the lava will hit city of Yogyakarta.
Rumors might be manifest of preparedness is to proceed to find the form of concrete. Without understanding the context of the threat of lava which empirical and reasonable risk assessment, the social process of preparedness keblinger a disturbing rumor. Also twisted so easily anticipated action-cost justification is more expensive than the value of its potential risks. Debt again. This is where preparedness so contrary to the goal, to reduce risk.
* * *
In the context of threats G. Merapi, lahars are the type of secondary threat. Primary threat hot clouds. The word lahar originated from Indonesia and has become a worldwide name for the phenomenon of sediment clouds of ash mixed with rain water hot.
Ash mixture with water to form viscous liquid and flows into the lower river follow the flow. Lava flow velocity of about 6 meters per second or between 20 to 30 kilometers per hour. Depending on the slope of the riverbed. The more oblique, the more profusely. The magnitude of flow, speed, and the duration of certain drainage, lahar could erode sand, soil and rocks at the base or the river bank in its path. This scouring material that makes lava become dangerous.
"If the flow is still viscous liquid mixture of ash and water do not bring other materials, it is still lava plain that is not harmful," said Subandrio. So not all the material into lava avalanches of lava domes. Only the ashes only.
The amount of rainfall that could trigger lava between 40 to 70 millimeters for 2 hours continuously. Another factor, the slope of the riverbed is steep. "The terms of the occurrence of lahar (ash content, the slope and the potential for rainfall) in S. Gendol fulfilled all, "said Subandrio. Just waiting for enough rainfall to come, will occur in Gendol lava.
More info on rain triggered lahars, Subandrio explained that average rainfall in the southern slopes of G. Merapi was relatively higher than in the western slope. That way, the sediment hot clouds on the southern slopes, lava chances become greater. According to data BPPTK, 60 percent incidence of lava G. Merapi triggered localized rain or rain on one side of the slope alone. The rest is triggered by rain overall in the region G. Merapi.
Rain early in the season according Subandrio will not cause the lava. At first the rain water will be absorbed by the hot clouds of ash deposits. Subsequently forwarded to the layer of sand and rock underneath. When the bottom layer is water saturated, the rain still continued, hot clouds of ash deposits come saturated and become lava. In low rainfall, rainwater beperan tamp hot clouds of ash deposition and material underneath.
* * *
Although the transport of sand and lava rocks, not necessarily a disaster. Genesis lava in G. Merapi, which impact the final disaster occurred in November 1975 and October 1976. Flow leads to S. Krasak and S. Pabelan on the west-southwest. This area into administrative regions and districts Srumbung Shaman, Magelang regency, Central Java. When the lava causes the bridge S. Krasak heavy damage. Bridge located on the main route overland transportation between Yogyakarta and Magelang.
Lava of 1975 and 1976 was the impact of a major eruption in 1961 that produced the material approximately 42 million cubic meters. Followed by eruption of small-corruption in 1972, 1974, and 1975 are increasingly adding the number of hot clouds of ash sediment, sand and stone. So that it becomes lava in great intensity.
Since the lava of 1975 and 1976, the government keen to build dams controlling the flow of lava-flow of the river is potentially occurred lava. Construction of this dam is a joint Government of Indonesia and Japan. Utangan financed with funds abroad, especially Japan through the Japan International Cooperation Agency (JICA), a Japanese government agency for international cooperation. The responsibility to conduct the construction of dams diampukan Merapi Project (total primary) and Sabo Technical Centre (STC) is the governing body of both the conduct of joint Japan-Indonesia to lava control projects, the scope of the Director General of Irrigation, Ministry of Settlement and Regional Infrastructure. After June 14, 2006, STC's total primary and the construction of 11 dams in controlling lava S. Gendol and S. Opaque. It is estimated that dams will be completed by December 2006 petengahan. SetIP dam unit cost about 3 billion dollars.
"After the 1970's the lava (in intensity, distribution, duration and frequency) that big never happen again in G. Merapi. Because there is no longer the eruption of 1961, "said Subandrio. But he did not declare a massive dam construction as an act of responding to the threat of lava disproportionately, as he stressed at the beginning of his presentation.
What is more important to understand common is the fact that the lava is no longer incident that caused loss of life human. "Since the 1970's there was no human casualties due to lava. If ever there are human victims in the future, meaning we experience a setback, "Subandrio again emphasized. According to past experience lava makes all parties to learn and better understand the character of lava. Besides the socio-political support and technical infrasuruktur better. Yes, mechanisms and its performance is another matter again.
The last lava G. Examples are the lava of Merapi in S. Boyong on the south side entrance Pakem subdistrict, Sleman, Yogyakarta, April 5, 1995. Lahar in S. Boyong a hot cloud deposition 1994. Both lava in S. Apu, on the southwest side in the sub-Selo, Boyolali district, Central Java. Lahar in S. Apu is a material erupted in the 1950s. A few days after the lahar that occurred in mid-August 204, the government held an auction Boyolali district to dredge sand from which accommodated the dam. There are no human casualties in the second incident that lava. Conversely, the advantage of sand and stone to be mined in order to restore the capacity of dams to hold the next lava.
* * *
Historically, lahars have occurred in S. Gendol. According to records BPPTK lava S. Gendol occurred in 1846. Causing damage to approximately 50 hectares of agricultural land. Then in 1906, at the time the activity G. Merapi heading south like today. The last occurred in 1930 until 1932 with the volume flow of about 2.5 million cubic meters.
Now with a volume of 10 million cubic meters of material according to Subandrio still not alarming. Directions to the dominant lava S. Gendol which is still pretty steep cliffs. In other words, S. Gendol still provide enough room to accommodate the flow of lava.
Subandrio also dismissed fears of a lahar in S. Opaque. According to the eruption of material that goes into S. Opaque about 300,000 cubic meters. BPPTK also no historical record of lava in S. Opaque, so that the community surrounding S. Opaque does not need to worry. "Lahar in S. Opaque will only occur if lava in Gendol occur on a scale so large that overflow into S. Opaque. The possibility of overflow is small "he said. Directions to the dominant fixed lava S. Gendol. On the possibility of overflow into S. Subandrio opaque detailing only if half of the material on S. Gendol come flowing together, it might overflow into S. Opaque. "If lava that occurs in S. Normal Gendol S. Opaque safe, "he continued.
River Opak not tipped in peak G. Merapi. This river section adjacent to S. Gendol. In the downstream, S. Opaque shrink the size of the irrigation canal with a settlement on the edge of either side.
* * *
To reduce the risk of lava threat that needs to be done according to Subandrio, the first is a map-making operations. Map includes identification of potential risk and evacuation routes in the region at risk. Map of course risks should be based on an analysis that could be accounted for. Both technically and socially. Second, early warning systems for communities in the area identified at risk. Third disseminating operational maps and early warning systems to communities at risk areas. Dissemination aims mawacanakan threat context, operational maps as well as capturing the idea for the improvement of preparedness concrete forms together.
Sabo Technical Centre has installed sensors to detect lava wire at several dams in S. Gendol. The sensor is a stretch of wire inductor is connected to a transmitter. Wire stretched at a certain height. If touched fluid lava, the wire will trigger the transmitter and the transmitter then sends a warning signal of danger. "Warning lava danger with this kind of sensor may be a little late. Because the new sensors would give a warning when it happens lava "said Subandrio.
According to him, better early warning system was combined with the use of rainfall data and acoustic detection sensors lava. The rainfall data is an early indicator, simple and can be done by the community. He pointed out if rain had occurred for 1 hour, then society must begin to increase alertness. If the rain continues, it may already have taken early action to save.
Acoustic sensor or AFM (acoustic flow meter / monitoring), such a vibration-detection seismo meters lava flow. This technology has been used in S. Boyong and managed to detect the lahar that occurred on April 5, 1995. "Thanks to the AFM in Kaliurang BPPTK officer can give a warning to miners of sand in Boyong so that no human casualties. Only trucks of sand are washed away and buried in mud, "she said.
At the end of his speech, stressed the need for rearrangement Subandrio tourism activities in the hamlet Kaliadem lava. This is to reduce the risk if there is lava. For example, by arranging tours opened early morning and close at 12.00. In the annals of lava, almost 80 percent of lava occurred in the afternoon because of rain usually lasts between 12.00 to 19.00. "So it is restructuring the economy will not turn off the community but a proof of hazard problem also taken into account by the tour organizers," Clearly Subandrio. Hamlet Kaliadem highest settlement on the edge of groove S. Gendol, about 7 kilometers from the peak G. Merapi. Formerly a favorite tourist sites after the Ground. On June 14, 2006 this location was destroyed by hot clouds and lava material that caused two fatalities. Activity tourism economy back on after it opened as a tourist loaksi lava.
In addition, he also stressed the need for simulation for the community and volunteers in the area at risk. With this simulation system of early warning and evacuation operations maps can be proven effective for service together. By doing so, hopes all parties would be more understanding of the mechanisms of action appropriate decision-making context of threats....

0 komentar:

Posting Komentar