LOKON VOLCANO - NORTH SULAWESI
Although inclement weather sometimes obscured views of Lokon-Empung's Tompaluan Crater, PVMBG reported that during 1-14 September observers at the post in Kakaskasen Tomohon (North Sulawesi, 4 km from the crater) saw white plumes rising as high as 250 m above the crater. The number of shallow volcanic earthquakes was the highest on 1 September (20 recorded), and then fluctuated between 1 and 4 per day during 2-14 September. The Alert Level remained at 2 (on a scale of 1-4). Residents and tourists were reminded not to approach the crater within a radius of 1.5 km.
Frequent activity at Lokon-Empung since early 2011 has typically included small explosions amid seismic unrest. Eruptions from the active Tompaluan crater, in the saddle between the peaks of Lokon and Empung, took place during September 2012-September 2013, May 2015, and August-September 2015. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). The Alert Level has been set at 3 (on a 4 level system) since July 2011, and residents and tourists have been warned not to approach the crater within a radius of 2.5 km.
Activity during 2011-2014. A brief explosion on 11 February 2011 was followed by an eruptive period lasting a year, from 26 June 2011 through 1 May 2012. Activity resumed again on 15 September 2012, and was continuing as of mid-April 2013 (BGVN 38:03). Although there were no further reports of explosive activity until September, thermal anomalies were observed on 5 July 2013 (2 pixels) at or near Tompaluan Crater, based on MODIS satellite data analyzed using MODVOLC.
An ash plume rising to an altitude of 1.8 km and drifting N on 9 September 2013 was reported by the Darwin Volcanic Ash Advisory Centre (VAAC) based on ground reports from PVMBG. Ash was not detected in satellite images due to meteorological clouds. According to a news article (Jakarta Post), an explosion at 0630 generated an ash plume that rose 1.5 km; the explosion was heard 10 km away. Darwin VAAC noted that during the next day, ash plumes rose to an altitude of 2.4 km, although ash was again not identified in satellite images. A spokesperson from the PVMBG told the Jakarta Post that activity declined after 9 September, including the frequency of deep and shallow volcanic earthquakes.
A year later, PVMBG reported that during 8-14 September 2014 observers saw white plumes rising 25-100 m above Tompaluan Crater. On 13 September three explosions from the crater, at 0300, 1146, and 1229, produced thick white plumes that rose at most 500 m above the crater. Seismicity decreased sharply after the 13 September events, but continued to remain high relative to the levels detected previously.
Activity during 2015. According to PVMBG, observers saw white plumes rising 25-50 m above Tompaluan Crater during 6-13 May 2015, although bad weather often prevented observations. Seismicity fluctuated but slightly decreased overall.
An eruption on 20 May 2015 from the crater generated an ash plume that, according to the Darwin VAAC, rose as high as 3 km and drifted NNW (figure 17). The eruption was accompanied by loud "thumping" noises heard at the local observation post. During 21-27 May, thick grayish-white plumes rose as high as 150 m. Bad weather prevented satellite views. Seismicity fluctuated but generally continued to decrease slightly.