Kamis, 05 Oktober 2017 18:58:20 WIB
A. Observational Data
2. Visual Observation
- The rate of volcanic earthquakes in the last 12 days has not accelerated but continues to fluctuate at high levels. In average, there are still 1-3 earthquakes per minute with the total number reaching greater than 600 per day.
- Shallow volcanic earthquakes from September 24 to October 5, 2017 have increased in number (generally more than 200 earthquakes per day) when compared with the previous period (generally less than 200 earthquakes per day). This may indicate that magmatic activity at shallow depths is still high.
- The largest earthquake to be recorded during this crisis is a M4.3 (27 September 2017 13:12 Central Indonesia Time/CIT UTC+8). It was felt in the local area with an intensity of MMI III-IV (Modified Mercalli Intensity). Most of the largest recorded earthquakes have a magnitude between M2.0-M3.0. The number of felt earthquakes at the Mt. Agung Volcano Observatory in Rendang village (AVO Rendang) (around 12.5 km to the South-Southwest of the volcano) reached a maximum on September 27, 2017 with 14 events. After that, the number of earthquakes felt at the AVO Rendang has decreased.
- Earthquakes are located under Mt. Agung with a range in depths up to 20km below the summit.
- Real Time Seismic Amplitude (RSAM) in the last 12 days has not increased but remains at a high level.
- Earthquake activity is still dominated by high frequency events. This indicates that seismic activity at the volcano still represents the brittle failure of rock inside the volcano in response to magmatic intrusion.
- Changes in seismic velocity indicate that pressurization under the volcano continues as the intruded volume of magma into the system increases and as magma moves towards the surface.
3. Satellite Remote Sensing
- Gas emissions from the crater, as observed from AVO Rendang (South sector) and AVO Batulompeh (North sector), appear as thin to thick white clouds that reach a height of 50-200 m above the crater rim.
- Satellites have detected steam emissions and thermal areas within the summit crater. During the crisis period, these areas have expanded along the north-east edge and including an area of emissions in the center of the crater.
- Water expulsion in the crater near the solfatara field has been observed by satellite. Water expulsion is thought to reflect a disturbance to the hydrologic system in response to intruded magma at depth.
- Tiltmeter observations showed a sudden deflation on October 1, 2017, but following days until today showed continued inflation.
- Differential optical absorption spectroscopy (DOAS) gas measurements made at a distance of 12 km from the summit did not detect any SO2. This lack of detection can not necessarily be interpreted as a lack of SO2 or magmatic activity. SO2 concentrations may be below the detection threshold of the instruments, or emitted SO2 content may be reduced due to scrubbing (removal of SO2 gas as a result of interaction with water).
- White smoke coming from the crater is potentially accompanied by the release of magmatic gases (CO2, SO2, etc.). If the concentration is high, these gases can smell, sting, and endanger the safety of those who inhale it. However, the current hazard from gas exposure is likely to be limited to the area around the crater. These gases will be easily blown and scattered by the wind so that the concentration will decrease significantly distance.
- MultiGas measurements at Mt. Batur do not indicate the supply of new magma under Batur. As of today, all indications suggest that all recent activity is related to Mt. Agung.