Mount Merbabu Mount Merapi Lahar hazards and risks following the 2010 eruption of Merapi volcano, Indonesia Lavigne F., Bélizal E., Cholik N., Nurnaning A., Picquout A., Mei E. Paris 1 Pantheon-Sorbonne University, Laboratory of Physical Geography, France, and Center of Volcanology and Geological Hazards Mitigation, Yogyakarta, Indonesia. 0 4 km Volume of pyroclastic debris likely to be removed by rain in valleys (in excess of 100 x 106 cubic-meters) much higher than those calculated after more conventional eruptions (less than 10 x 106 cubic-meters); A new context for lahar occurrence (lahar = volcanic debris flows or hyperconcentrated flows) Most of the Sabo dam structures have been filled by the 2010 pyroclastic flows or subsequent lahars The eruption occurred at the beginning of the current rainy season, which is more rainy than usual (rainfall typically 4000 mm per year 1500 m a.s.l.), due to the occurrence of La Niña. GENDOL, Sindumartani, 28 février 2011, 14h30 Some channels totally filled by pyroclastic flows => need artificial path needed for lahars GENDOL, Sindumartani, 28 février 2011, 16h30 High risk within the Gendol valley Goals of the study • To build a database on lahar occurrence since the 2010 eruption of Merapi; • To study the geomorphological changes of the valleys drained by lahars; • To assess the economic and social effects of the lahars on the territory, and the lahar risk management. Methods • Field observation and measurements of lahars in motion and lahar deposits; completed by secondary data (e.g. U- Tube !) • Analysis of AFM signals and webcams • Laboratory analysis (sedimentology and photointerpretation) • Inquiries Tens of lahars already occurred in 16 river channels Trising Woro Apu Batang Temporary data February 2010 5% 1% 8% 1% Bebeng 2% Blongkeng Number of lahars Senowo 35 9% 1% Boyong 30 10% 25 Putih 20 21% Gendol 7% 15 10 Juweh 6% 5 0 Pabelan Ladon Krasak 4% Opak 7% 4% 8% Kuning Lamat 5% 1% Geomorphological effects of lahars River bank erosion and riverbed incision - 15 m 5,3 m - 20 m - 5 m 23 m Lahar deposition Inverse grading Senowo River, lahar 9-10/01/2011 Distribution of pyroclastic material Boulder deposition in Jumoyo village 3/1/2011 Excess of sedimentation downstream of the Putih River Former depth: 12 m New lahar path along the Putih River through the village of Sirahan Road destruction by the 9 January lahar Incision of the new channel by the (photo: 10 January) 23 January lahar (photo: 27 January) 8 m 3 m 4 m road 1 m Damages by lahars Damages on settlements Destruction of Jumoyo village 3/1/2011 One hundred houses destroyed or damaged Destruction of commercial buildings Damages on agricultural land Submersion by lahars Loss of ricefield by bank erosion A threat for water network Sedimentation issues in the Mataram Canal Water network crossing the Opak River High sediment load in the Progo River Disturbance of circulation network Destruction of bridges N Magelang Merapi To Solo Menoreh Hills ? Yogyakarta 0 20 km Disturbance of the sand mining operational system A danger for the people - 2 fatalities - People wounded or burned Lahars as a touristic attraction Hazard map and lahar detection from CVGHM: AFM and webcams 4500 4000 3500 ) 6 - 3000 Risk prevention 2500 2000 1500 Vs (cm/s. x 10 1000 1. Institutional measures 500 0 15:28 15:36 15:44 15:52 16:00 16:08 16:16 16:24 16:32 16:40 16:48 16:56 17:04 Information Restriction of access 2. Universities and NGO’s actions 3. Community-based measures Physical self-protection Gendol R. Putih R. Risk perception of lahar – December 2010 Not frightened A bit frightened Frightened Very frightened Lamat Blongkeng Bebeng 23,3 18,7 32,0 43,3 45,0 55,0 33,3 49,3 Woro 38,9 55,8 5,1 Pabelan 32,9 31,6 5,3 30,4 6,7 20,0 Putih 73,3 8,8 Opak Boyong 15,8 25,0 Krasak 27,5 46,4 19,7 5,0 44,8 64,5 42,5 No DUSUN DESA 1 1 Kinarejo Umbulharjo 2 Petung 5 km 2 Kepuharjo du cratère 3 Kopeng 1 4 Salam 3 5 Geblok Wukirsari 6 Ngemplak 4 7 Panggung 8 Teplok Argomulyo 5 9 Kebur 6 10 Banjarharjo Bimomartani 15 km 7 Posko along the Opak River du cratère 8 - Radio borrowed by NGO’s - Connection to radio frequency 9 - Problem: uncontroled information, confusion between 10 foods and lahar, false alarms 11 1 km N 23 km du cratère Thank you for your attention.