Steep increase in seismicity during February-March 2012

According to the Center of Volcanology and Geological Hazard Mitigation (CVGHM), Lamongan has not erupted since 1898. On several occasions since then, however, seismic activity has increased. Brief periods of earthquakes and earthquake swarms occurred in 1924-25, 1978, 1985, and 1988 (SEAN 10:10, 10:11, 13:02). The Darwin Volcanic Ash Advisory Centre (VAAC) reported on 24 September 2003 that aircraft personnel had observed ash over the volcano to a height of about 900 m, but this was not confirmed by on-scene observers (BGVN 28:12). Our previous report noted continuous tremor and an earthquake swarm on 5-6 January 2005 (BGVN 31:01).

CVGHM reported that during 1 February-9 March 2012, diffuse white plumes rose at most 20 m above Lamongan's crater. Seismicity increased on 23 February, then fluctuated in intensity through 7 March. Seismicity increased significantly on 8-9 March (table 1). CVGHM raised the Alert Level to 2 (on a scale of 1-4) on 9 March, and began to monitor the volcano more intensively. Residents and tourists were prohibited from going within a 1-km-radius of the active crater. No eruptions occurred during the reporting period. Increased seismic activity at Lamongan continued at least through 12 March.

Table 1. Seismicity at Lamongan during 1 January-9 March 2012. Data from CVGHM. Shallow volcanic earthquakes were not reported and categories were not defined in the reports.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

October 1985 (SEAN 10:10) Cite this Report

Seismic swarm near site of 1924-25 and 1978 swarms

"Lamongan experienced a seismic swarm with ground breakage 2-15 October. More than 3,000 earthquakes were recorded at the VSI observation post at Gunungmeja, near Klakah, W of Lamongan (figure 1). Two additional seismometers were installed in the epicentral area on 5-6 October. Ground breakage occurred in a region ~5 km W of the summit and consisting of numerous ground cracks, some with vertical offsets of 15 cm, striking ENE. No changes were noted in the temperatures or character of the many lakes in the Lamongan area, which fill maars created by prehistoric eruptions. The 1985 activity is in the same general area as two seismic swarms that occurred in 1924-25 and in 1978 but did not culminate in eruptions."

Figure 1. Map of Lamongan, after Van Bemmelen, 1949. Contour interval is 250 m. Contours on the W side of the map mark the lower E flank of Tengger Caldera. Fissures shown are from the 1924-25 earthquake swarm.

"Lamongan was quite active during the 19th century with 40 eruptions, including more than a dozen that produced lava flows. Most were from vents located on the W flank above about 400 m altitude. It is notable that the maars on the W slope of Lamongan all occur at elevations below the historic eruption vents, suggesting that the position of the groundwater table controls its eruptive style. Eruptions from above 400 m altitude form fissure vents and cinder cones that pose little threat to the local inhabitants. Activity from vents below 400 m may give rise to explosive, maar-forming eruptions. The 1985 epicentral area has a surface elevation of 200-380 m. Plans are underway to increase the level of surveillance."

Reference. Van Bemmelen, R., 1949, The geology of Indonesia, v. 1B: M. Nijhoff, The Hague.

Information Contacts: J. Matahelumual, Suparto S., and T. Casadevall, VSI.

November 1985 (SEAN 10:11) Cite this Report

Seismicity declines

"November activity consisted of an average of one earthquake/day in the October swarm area W of the volcano. Detailed geological and monitoring efforts are now in progress by VSI to evaluate the possibility of a future eruption from the epicentral area."

Information Contacts: T. Casadevall and L. Pardyanto, VSI.

February 1988 (SEAN 13:02) Cite this Report

Increased seismicity but no temperature changes

A brief seismic swarm centered immediately W of Lamongan cone began on 8 February at 0445. Additional seismicity was recorded through February. No changes have been noted in the temperature or behavior of the maar lakes within the epicentral region. The earthquakes occurred in virtually the same epicentral area as those from the 1978 and 1985 swarms.

Information Contacts: VSI.

December 2003 (BGVN 28:12) Cite this Report

Pilot notes 24 September ash emission, but it lacks ground confirmation

When last discussed in 1988 (SEAN 13:02), a seismic swarm had occurred here. Except for an uncertain 1953 eruption, 20th- and 21st-century eruptions are unknown. Darwin Volcanic Ash Advisory 2003/1 notified aircraft personnel that, on 24 September 2003, ash was visible to ~ 900 m over Lamongan.

In this 2003 case, no confirmations of a plume or other signs of volcanism were available from observers on the scene. Concrete confirmations can establish that the plume did indeed vent here, rather than at another volcano and that it did not result from similar-looking processes of non-volcanic origin (eg., forest fires, crop burning, lofted dust).

Information Contacts: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

January 2006 (BGVN 31:01) Cite this Report

Above-background seismicity during 5-6 January 2005

Elevated seismicity occurred at Lamongan on 5-6 January 2005. From 1200 to 0700 on 5 January, 22 events occurred with Modified Mercali Intensity (MMI) of 1. At each of three times (0331, 0447, and 0524) observers noted an event of MMI 3. During this period, instruments detected continuous tremor with an amplitude of 3 to 15 mm. On 5 January there were 282 local tectonic earthquakes and 53 volcanic A-type earthquakes. The volcano alert level was raised to 2.

On 6 January 2005, 107 volcanic A-type earthquakes were recorded. Local tectonic earthquakes over the two day period occurred 159 times, of which 10 of them were events had Modified Mercali Intensity (MMI) of 1-3.

Information Contacts: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

February 2012 (BGVN 37:02) Cite this Report

Steep increase in seismicity during February-March 2012

According to the Center of Volcanology and Geological Hazard Mitigation (CVGHM), Lamongan has not erupted since 1898. On several occasions since then, however, seismic activity has increased. Brief periods of earthquakes and earthquake swarms occurred in 1924-25, 1978, 1985, and 1988 (SEAN 10:10, 10:11, 13:02). The Darwin Volcanic Ash Advisory Centre (VAAC) reported on 24 September 2003 that aircraft personnel had observed ash over the volcano to a height of about 900 m, but this was not confirmed by on-scene observers (BGVN 28:12). Our previous report noted continuous tremor and an earthquake swarm on 5-6 January 2005 (BGVN 31:01).

CVGHM reported that during 1 February-9 March 2012, diffuse white plumes rose at most 20 m above Lamongan's crater. Seismicity increased on 23 February, then fluctuated in intensity through 7 March. Seismicity increased significantly on 8-9 March (table 1). CVGHM raised the Alert Level to 2 (on a scale of 1-4) on 9 March, and began to monitor the volcano more intensively. Residents and tourists were prohibited from going within a 1-km-radius of the active crater. No eruptions occurred during the reporting period. Increased seismic activity at Lamongan continued at least through 12 March.

Table 1. Seismicity at Lamongan during 1 January-9 March 2012. Data from CVGHM. Shallow volcanic earthquakes were not reported and categories were not defined in the reports.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).