MAGELANG - Merapi’s cold lava flood is still largely threatening, especially along the Kali Putih river in Magelang, Central Java, after the surging flood on Monday (3/1). This is based on several reasons, including the low rate of rainfall in the peak of Merapi as reported by the Babadan observation post and the condition of dams along the course of Mount Merapi flow which has been covered by volcanic material.
Merapi volcanic material piled in because some river flows below Mount Merapi, such as Kali Blongkeng, Batang, and Lamat are dammed and united toward the Kaliputih dam. As a result, during heavy rain, the surge of cold lava flows to Kali Putih only, making it unable to contain the material.
"With that condition, the potential of Merapi’s cold lava flood which brings greater material continues to threaten residents, especially along Kali Putih," said volcanology scientist from the Geology Department of UGM, Ir. Bambang Widjaja Hariadi, when he was monitoring Kali Putih on Tuesday (4/1). Bambang monitored the location together with the Chairman of UGM Department of Geology, Prof. Ir. Dwikorita Karnawati, M.Sc., Ph.D.
Bambang added that the dredging process of Merapi’s volcanic material around the upstream dam of Kali Putih was quite risky. The material, mainly sand, is placed just in close proximity to the river stream. When the rain is heavy, the sand will be eroded and carried away by water. As a result, the dredging will increase the amount of volcanic material that is carried by the waterflow. Bambang also believed the volcanic materials which caused the flooding were not the material from the recent eruptions but the 2006 eruption.
"It is right that the material is dredged, but don't put it near the river. If heavy rains occur, the rain will erode the material again, thus a bigger amount of material," said Bambang.
Meanwhile, Dwikorita observed the ultrasonic installation as a monitoring tool of the approaching sound vibration of cold lava flood is not quite fit. The tool is set too high from the river, so it is a bit late to give a sign when the flood came. "I saw it was a bit high. It should be installed slightly below, nearby the river, although it is somewhat risky," said Dwikorita.
Dwikorita and Bambang also agreed that to reduce the greater impact of the surge of Merapi’s cold lava floods in the near future, some anticipation should be done. Some immediate steps that can be done, among others, are by re-opening several dams that are closed like in Kali Blongkeng, Lamat and Batang. So, the stream will not only flow to Kali Putih. In addition, early warning system needs to be optimized. Also, residents need to be temporarily relocated during floods.
"It may take some time for infrastucture improvement, so residents need to be temporarily relocated if there is possible flooding. In addition, the distribution of leaflets and pamphlets about the cold lava flood hazard needs to be encouraged," said Dwikorita.
The monitoring by UGM geologists is conducted at the downstream of Kali Putih and Talun area that is the meeting point of the Pabelan and Senowo River currents, up to the Merapi volcano observation post at Babadan, Dukun, to determine the rainfall rates at the peak.
The dredging process of the Merapi volcanic material is still noticeable. Resident houses are also damaged and some even buried in the sand and mud up to five feet high.
The impact was admitted by the residents to be larger than the previous flooding on December 8, 2010. Thousands of residents fled to other places, some fish ponds also hit by the flood. As told by Sunarjo (61) from Jumoyo, his loss was up to 18 million IDR because all of his three fishing ponds were hit by the floods.
“There are two fishing ponds and one fish raising pond wrecked by the flooding. The losses could reach 18 million IDR, Sir," said Sunarjo.
In the flood in Kali Putih on Monday night, more than 50 homes were damaged and thousands of residents displaced. Hundreds of surrounding rice fields were damaged and eroded. The Yogyakarta-Semarang highway in the Jumoyo village was closed due to overflowing sand and stones up to 300 meters in length and about 2 meters high.