Hazard Levels
Hazard levels at Merapi are based on instrumental and visual observations, and are as follows:
Level 1: The volcano is experiencing normal activity.
Level 2: Both visual and seismic data indicate an increase in activity.
Level 3: Activity is continuing to increase; there is a concern that an eruption will occur.
Level 4: The eruption has initiated.
Level 1: The volcano is experiencing normal activity.
Level 2: Both visual and seismic data indicate an increase in activity.
Level 3: Activity is continuing to increase; there is a concern that an eruption will occur.
Level 4: The eruption has initiated.
Monitoring tools
Volcano monitoring at Mt Merapi dates back to 1920, where Dutch colonists set up one of the first volcano monitoring establishments in world, the Netherlands East Indies Volcanological Survey. This establishment was to be later changed to the current survey, the Volcanological Survey of Indonesia. Five observation stations are positioned within 15 km of the volcano, and the Merapi Observatory and Technology Center is located ~28km south in Yogyakarta. The following monitoring tools are in permanent use around Merapi volcano.
Tiltmeters: A number of tilitmeters are set up around the volcano's summit to analyze inflation and deflation of the volcano.
Electronic Distance Measurements: These measurements are performed from the five observation stations on the volcano. This method utilizes reflectors at high elevations to measure the distance of the stations from the volcano. Lessening of the distance between the station and reflectors corresponds to inflation of the volcano.
Seismometers: Four short-period permanent seismic stations are set up within 7km of the volcano's summit. Temporary stations are also frequently in use at Merapi. Seismic signals observed at Merapi include volcano-tectonic, low-frequency, multiphase (hybrid), rock fall, and very-long period events.
Satellite, visible, and near-visible imagery: Satellite data used on Merapi during the 2010 eruption (Suruno et al. 2012) included Synthetic Aperture Radar (COSMSO SkyMed RADARSAT-2, TerraSAR-X sensors), thermal infrared (ASTER sensor), and high-resolution visible and near-infrared (GeoEye- 1 and WorldView-2 sensors). These images can be used to observe changes on the volcano summit crater, lava dome growth, vent features, and also pyroclastic flows.
Figure 26: Illustration of monitoring stations around Mt Merapi. Modified from Surono et al. (2012).
Gas monitoring: Gas emissions are regularly sampled in the field from vents around the summit (e.g. Woro solfatara). Gases analyzed include H2O, H2S, SO2, CO2, HCL, H2, O2, and CH4. Ground-based ultra-violet Gas Spectroscopy is also utilized at Merapi, and is particularly useful when areas are inaccessible due to volcanic activity.
Tiltmeters: A number of tilitmeters are set up around the volcano's summit to analyze inflation and deflation of the volcano.
Electronic Distance Measurements: These measurements are performed from the five observation stations on the volcano. This method utilizes reflectors at high elevations to measure the distance of the stations from the volcano. Lessening of the distance between the station and reflectors corresponds to inflation of the volcano.
Seismometers: Four short-period permanent seismic stations are set up within 7km of the volcano's summit. Temporary stations are also frequently in use at Merapi. Seismic signals observed at Merapi include volcano-tectonic, low-frequency, multiphase (hybrid), rock fall, and very-long period events.
Satellite, visible, and near-visible imagery: Satellite data used on Merapi during the 2010 eruption (Suruno et al. 2012) included Synthetic Aperture Radar (COSMSO SkyMed RADARSAT-2, TerraSAR-X sensors), thermal infrared (ASTER sensor), and high-resolution visible and near-infrared (GeoEye- 1 and WorldView-2 sensors). These images can be used to observe changes on the volcano summit crater, lava dome growth, vent features, and also pyroclastic flows.
Figure 26: Illustration of monitoring stations around Mt Merapi. Modified from Surono et al. (2012).
Gas monitoring: Gas emissions are regularly sampled in the field from vents around the summit (e.g. Woro solfatara). Gases analyzed include H2O, H2S, SO2, CO2, HCL, H2, O2, and CH4. Ground-based ultra-violet Gas Spectroscopy is also utilized at Merapi, and is particularly useful when areas are inaccessible due to volcanic activity.
Monitoring of the 2010 eruption
The 2010 eruption provides a good example of current monitoring at Merapi and the typical signals of an impending eruption. The events leading up to the eruption are documented in detail by Suruno et al. (2012). Although the 2010 eruption is considered a large, 100-year event, precise forecasting and timely issuing of warnings from the Indonesian Center of Volcanology and Geological Hazard Mitigation is thought to have saved the lives of anywhere between 10,000-20,000 people.
In November 2009, the earliest signs of unrest were detected using Electronic distance measurements, which showed inflation of the volcano after a period of deflation that followed the 2006 eruption (Suruno et al. 2012). In addition, three volcano-tectonic (VT) earthquake swarms were observed between October 31, 2009, and June 10, 2010. During September 2010 increasing inflation (Figure 27A), earthquake counts and seismic energy release (Figure 27B) were observed in addition to increased temperature, CO2, and H2S abundances at summit fumaroles (Figure 27C). These observations led to the raising of the alert level to Level 2 on September 20.
From September 20 to October 26 a dramatic increase in activity was observed in all monitoring devices. The southern flank experienced increasing deformation, indicated by a reduced distance of the southern volcano flanks to the observation stations (Figure 27A). The rate of seismicity continued to increase as well as the ratio of volcano-tectonic to hybrid events, indicating potential magma movement. Additionally, increased CO2/SO2 and H2S/SO2 ratios, number and magnitude of rock falls, and low frequency earthquakes occurred from October 1-19, and the alert level was raised to Level 3 on October 21. When seismicity increased to unprecedented levels on October 25, the alert was raised to Level 4; 35 hours later, Merapi began to erupt.
In November 2009, the earliest signs of unrest were detected using Electronic distance measurements, which showed inflation of the volcano after a period of deflation that followed the 2006 eruption (Suruno et al. 2012). In addition, three volcano-tectonic (VT) earthquake swarms were observed between October 31, 2009, and June 10, 2010. During September 2010 increasing inflation (Figure 27A), earthquake counts and seismic energy release (Figure 27B) were observed in addition to increased temperature, CO2, and H2S abundances at summit fumaroles (Figure 27C). These observations led to the raising of the alert level to Level 2 on September 20.
From September 20 to October 26 a dramatic increase in activity was observed in all monitoring devices. The southern flank experienced increasing deformation, indicated by a reduced distance of the southern volcano flanks to the observation stations (Figure 27A). The rate of seismicity continued to increase as well as the ratio of volcano-tectonic to hybrid events, indicating potential magma movement. Additionally, increased CO2/SO2 and H2S/SO2 ratios, number and magnitude of rock falls, and low frequency earthquakes occurred from October 1-19, and the alert level was raised to Level 3 on October 21. When seismicity increased to unprecedented levels on October 25, the alert was raised to Level 4; 35 hours later, Merapi began to erupt.
Figure 27: Deformation (A), seismic (B), and gas (C) data leading up to the 2010 eruption. A and B also include the hazard levels that were implemented during this time. Seismic signals presented in B include volcano-tectonic (red), hybird (green), and low frequency (yellow). From Surono et al. (2012).
Internet monitoring
The website below provides up-to-date reporting on Merapi's activity and seismic data. The website is however in Indonesian. A webcam is also available for viewing.
http://merapi.combine.or.id/
http://merapi.combine.or.id/cctv/webcam-merapi/?lang=id