Berita

BANDUNG – Mt. Anak Krakatau is an active volcano located at the Sunda Strait, emerging among the islands of Panjang, Sertung and Rakata (the Mt. Krakatau complex).

Since its formation on 11th June 1927 until 2011, Mt. Anak Krakatau has erupted more than 100 times, both of explosive as well as of effusive nature, and has a repose interval of 1-6 year.

Mt. Anak Krakatau is currently in the process of ‘developing’ itself. Since its last eruption in 2001, the volcano has resumed its activities from 23rd October 2007 until 10th July 2011. The eruption occurs every year but the number of the explosive eruption as well as the hazard potentials  continually decrease. Mt. Anak Krakatau activities status was lowered, from Watch to Advisory, on 31stOctober 2009.

The seismograph at Mt. Anak Krakatau’s volcano observation post has not been able to record any quakes since 10th July 2011 because the field seismic equipments were damaged by material from the explosive eruption.

II. OBSERVATION RESULTS

The visual and seismic observation of Mt. Anak Krakatau activities are carried out at 2 observation posts: one at Pasauran Village, Cinangka Sub-district, Serang Regency, Banten Province and the other at Hargo-Pancuran Village, Kalianda Sub-district, South Lampung Regency, Lampung Province.

The seismic data obtained from the field will be telemetrically transferred to both observation posts, and through VSAT (satellite), the data will be further transferred to the office of the Center for Vulcanology and Geological Hazard Mitigation in Bandung.

2.1. Visual appearance

In general, visual observation from the Pasauran observation post has been frequently obstructed because the volcano is often covered by fog.

From the beginning of 2011 until 13th September 2011, several explosive eruption were seen, emitting volcanic ash and material spew.

The field observation of Mt. Anak Krakatau activities for the period of 14th to 30th September 2011 is as follows:

There was no ash eruption and almost half of the volcano’s sides at the north-east-south parts were covered by solfatara fields.

The activities at the crater were dominated by gusts of thin-moderate smoke along the crater walls and thin gust at several solfatara fields.
Tremors occuring at the volcano’s sides can be sensed from a distance of  ± 700 m from the crater.

2.2. Seismic activities

Seismic method has been carried out to monitor Mt. Anak Krakatau magmatic activities through the recorded seismic data, both the analog and the digital data received by the observation posts.

During the 2011 eruption period, there are 20-30 deep-volcanic earthquakes daily, 120-135 shallow-volcanic earthquakes, while explosion earthquakes and blast earthquakes may number to hundreds of occurences per day.

Until 10th July 2011, Mt. Anak Krakatau activities had been dominated by volcanic earthquakes (both deep-volcanic earthquakes and shallow-volcanic earthquakes), explosion earthquakes as well as blast earthquakes.

After the seismic equipment are back to normal, the volcano’s seismic activities are still high. From 18th September 2011 at 11.49 until 30th September 2011 there had been swarm volcanic earthquakes. The recorded volcanic occurences have counted to 4-5 times per minute.

III. Hazard Potential of Mt. Anak Krakatau Eruption

Mt. Anak Krakatau explosive eruption during the last 4 years (October 2007 until 2011) are magmatic strombolian eruption, namely explosive eruption that produces volcanic material in the size of clump, bomb, lapillli and ashes that usually scattered around the volcano within a radius of 500 m – 1,500 m, while the spread of the volcanic ash will depend on the wind strength and directrion.

The explosive eruption on 10th July 2011 at 03.26 pm damaged the seismic equipment mounted on the volcano, due to the spew of burning material in the radius of 700-1,000 m from the eruption center. Aside from damaging the seismic equipment, the eruption also damaged GPS measurement point installed at several location on the sides of the volcano.

Based on the Map of the Disaster-prone Area (Kawasan Rawan Bencana or KRB), almost all parts of Mt. Anak Krakatau sides which diameter is ± 2 Km belong to disaster-prone area. The high occurence of volcanic earthquakes which will potentially result in explosive eruption on the one hand and the high interest that foreign and domestic tourists have to visit, land and climb to the crater of Mt. Anak Krakatau on the other hand will potentially increase the risk of hazard. As a result, warning should always be given in order to prevent casualties.

IV. Summary

There has been an increase to the volcanic activity of Mt. Anak Krakatau, which is indicated by the occurrence of swarm volcanic earthquakes and the spread of solphatara zone on the sides of the volcano.

Based on the result and analysis to the visual and instrumental data, effective from 30th September 2011 at 12.00 pm the activity status of Mt. Anak Krakatau is raised from Advisory (Level II) to Watch (Level III).

Intensive monitoring will always be carried out to evaluate Mt. Anak Krakatau activities. Should there be any significant changes to the volcanic activities, the activity level will be adjusted accordingly.

V. Recommendation
With regards to the above-mentioned development, we’d like to recommend the following:

People/tourists are not allowed to come near Mt. Anak Krakatau Island within the radius of 2 km from the crater.

The communities who live in the coastal areas of the Provinces of Banten and Lampung are expected to remain calm and unprovoked by issues about Mt. Anak Krakatau erruption that will cause tsunami.

The communities who live in the coastal areas of the Provinces of Banten and Lampung are expected to remain calm, carrying out their daily activities while at the same time to constantly follow the direction from the local Satlak PB and Satkorlak PB.

For information, please contact the Center for Vulcanology and Geological Hazard Mitigation at (022) 7272606 at Bandung (West Java Province) or Mt. Krakatau observation post at (0254) 651449 at Pasauran (Banten Province). (IY)