Berita

The evaluation of Mt. Anak Ranakah activity in Manggarai District and East Manggarai District, Nusa Tenggara Timur Province:

1. Introduction

Mt. Anak Ranakah is located in Manggarai District and East Manggarai District, Nusa Tenggara Timur Province. Geographically, Mt. Anak Ranakah is in 08°38’06” SouthLat. and 120°31’56” EastLong. in height 2247.5 m dpl (above the sea level). Mt. Anak Ranakah is located in North Slope and is the youngest lava dome of lave dome series lining concentrically around Pocok Leok Caldera. Volcanic activity of the mount was started by the explosion happened on December 28th, 1987 such as freatic explosion. On January 11th, 1988 a big explosion happened in ash height about 8.000 m and also followed by pyroclastic flow heading to Wae Reno and Wae Teko in nort of the volacno. Its explosion period was unknown because the first explosion known was only in 1987 and up to now there is no explosion. The last result of eruption is the appearance and growth of lava dome. The status of Mt. Anak Ranakah since September 8th, 2011 at 4 p.m. WITA (Central Indonesia Standard Time) increased from Advisory (Level II) to Watch (Level III).

2. Evaluation

Based on daily release energy of volcanic quake since July 1st, 2011 up to October 6th, 2011, the highest energy release was at August 15th, 2011 by relatively decrease trend up to October 20th, 2011.

According to measure of MEMR since September 29th, 2011 up to October 6th, 2011, the distance of POS-AR1 has elongation trend since October 2nd, 2011 up to October 6th, 2011 by its maximum value 1.1 cm. The distance of POS-AR2 has shortening trend since September 29th, 2011 up to October 2nd, 2011 by its maximum shortening value 0.5 cm and having relative trend and deformation did not occur since October 2nd, 2011 up to October 6th, 2011.

3. Danger Potency

The lava dome volume of Mt. Anak Ranakah is risky towards the disturbance because of gravitation and pressure from inside the volcano, so it is often seen landslide from lava dome. The material landslide from lava dome in a big volume will form phyroclastic flow. Recently, area in high risk of pyroclastic flow is about 2 km heading to northwest – north of the crater which is surrounding Wae Reno River Valley.

4. Decision

•    Based on visual data analysis, deformation, and seismic, then commencing from October 22nd, 2011 at 2 p.m. WITA, the status of Mt. Anak Ranakah decrease from Watch (Level III) to Advisory (Level II).

•    If the activity of Mt. Anak Ranakah decreased/increased, its activity followed based on its activity level and threat.

•    An intensive supervisory will continuously be done to evaluate Mt. Anak Ranakah activity and also understanding of Mt. Anak Ranakah activity has to be done by socialization about the danger of Mt. Anak Ranakah treat.

5. Recommendation:

Based on the status of Mt. Anak Ranakah, so here are the recommendations:

1.    Citizens surrounding Mt. Ranakah and visitors/tourism may not do activity surrounding the crater (lava dome);

2.    Citizens surrounding Mt. Ranakah to be calm, not be influenced by irresponsible issue of Mt. Ranakah explosion;

3.    Center for Vulcanology and Geological Hazard Mitigation, Geological Agency always coordinate with the Government of Nusa Tenggara Timur (as the Head of SATKORLAK PB) and the government of Manggarai District and East Manggarai District (the head of SATLAK PB) about the activity of Mt. Ranakah. Citizens have to obey the instruction of SATLAK PB and SATKORLAK PB;

4.    The local government always coordinates with Observation Post of Mt. Anak Ranakag in Landu Village, Ruteng Sub-District, Manggarai District or Center for Vulcanology and Geological Hazard Mitigation in Bandung. (AK)