Volcanos

Roundup of Global Volcanic Activity – New Activity for the week of 22 November – 28 November 2017

Agung | Bali (Indonesia) : PVMBG reported that at 1730 on 25 November, after the number of volcanic earthquakes significantly increased, ash plumes rose 1.5 km above Agung’s crater rim and drifted 12 km WSW. Ashfall was reported in areas SW including Besakih (7 km SW), hamlets in the upper part of Pempatan (7.5 km W), and Temukus, prompting remaining residents to evacuate to the S. Eight inbound and 13 outbound international flights were cancelled, affecting 2,087 passengers. Crater incandescence was observed at 2100, signifying the presence of lava in the crater. BNPB noted that the number of evacuees was 25,016 (spread out in 224 shelters)

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On 26 November dark gray ash plumes rose 2 km at 0505, 3 km at 0545, and 4 km at 0620, and drifted E and SE. Ash emissions continued throughout the day; a few explosions were heard within a 12-km radius. PVMBG issued a Volcano Observatory Notice for Aviation (VONA) elevating the Aviation colour Code from Orange to Red. Satellite data recorded sulfur dioxide gas concentrations ranging from 1,000 to 2,000 tons/day. Ashfall was reported in several areas downwind including North Duda (9 km S), Duda Timur (12 km S), Pempetan, Besakih, Sideman (15 km SSW), Tirta Abang, Sebudi (6 km SW), Amerta Bhuana (10 km SSW) in Klungkung, and some villages in Gianyar (20 km WSW). Ashfall was the thickest (5 mm) in Sibetan (11.5 km S). News sources noted that Lombok International Airport closed during 26-27 November.

PVMBG raised the Alert Level to 4 (the highest level on a scale of 1-4) on 27 November, and the exclusion zones were expanded to a general 8-km radius and to 10 km in the NNE, SE, S, and SW directions. Dense ash plumes continued to rise 2-4 km above the crater rim. Based on satellite data, the Darwin VAAC reported that ash plumes rose as high as 9.1 km (30,000 ft) a.s.l., or just over 6 km above the crater rim. Pictures and video showed a white steam plume adjacent to a gray ash plume rising form the crater, signifying two distinct active vents. According to news articles the Ngurah Rai International Airport in Bali closed due to the airborne ash. On 28 November BNPB noted that the number of evacuees had increased to 38,678, and were distributed in 225 evacuation centers. The Ngurah Rai International Airport reopened on 29 November, after the Aviation colour Code was lowered to Orange.

Great Sitkin | Andreanof Islands (USA) : Recent observations of a robust steam plume and a period of gradually increasing seismicity over several months at Great Sitkin prompted AVO to raise the Aviation colour Code to Yellow and the Volcano Alert Level to Advisory on 22 November. On 19 November local observers photographed a light-coloured vapor plume rising about 300 m above the vent and drifting 15-20 km S. A satellite image acquired on 21 November showed steam continuously jetting from a small fumarole on the W side of the 1974 lava flow within the summit crater, and at least one area where snow and ice had been melted.

Seismicity had fluctuated but increased overall since July 2016, most notably in June 2017. The seismic activity was characterized by earthquakes less than M 1, and occurred either just below the summit or just offshore the NW cost of the island, 30 km below sea level. Possible explosion signals were recorded in seismic data on 10 January and 21 July 2017, but there were no confirmed emissions.

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