Cold lava floods that hit several rivers in Yogyakarta and Magelang, Central Java, resulted in quite immense economic losses. In fact, the impact of floods that overflowed the Jogja-Magelang main road forced many modes of transportation to use alternative pathways. "Quite many transportation stakeholders complain because the mileage get farther and passengers have decreased drastically," said M. Pramono Hadi at the UGM Center for Transportation and Logistics Studies (Pustral) on Thursday (27/1).
In the paper Determination Method of Disaster Risk toward Transportation System, Case of Merapi Volcano’s Slopes after Eruption 2010, Pramono Hadi said that the loss not only reaches up to billions of rupiah in terms of economy, but also physical, social, cultural, and others. Therefore, the method of determining the risk of disasters on transportation systems becomes very important.
The eruption of Merapi, Pramono continued, has thrown more than 120 million meter3 pyroclastic material on the brink of the slope, so it is quite normal that the cold lava floods nowadays are very immense. La-Nina phenomenon is another factor. "The high rainfall rate which continues to increase in this region is expected to last until mid-2011. The lava flood is the secondary danger of eruption. Therefore, it is possible if the rivers on the slopes of Merapi become the media to carry the sediment downstream," said Pramono Hadi.
As a guest speaker in a monthly discussion on UGM Pustral, Pramono said that the surge of sediment forces the policy of one way at a time for the main road of Jogja-Magelang. At least, this policy has been enforced ten times. "If only the condition is no longer feasible, maybe one day the road will be permanently closed for a long time considering the need to create and improve rivers channels in the area," he said.
Pramono explained that the ideal kurtosis characteristic of mountain for stability is 30%. If the mountain kurtosis reaches up to 45%, it will make some material to sag. Meanwhile, dams which are built within certain limits cannot withstand cold lava material. "With the continuous rainfall, it is only natural that some rivers have silt so that the section that should be channeling the material diminishes. This certainly increases the risk that may arise," he explained.