********************************** Montserrat Volcano Observatory Report for the period midday 29 December 2006 to midday 05 January 2007 From: Vicky Hards <vicky@xxxxxx> ********************************** Rapid dome growth continues, focused primarily on the north-western quadrant, which is now the highest part of the dome complex. During the reporting period an increasing number of pyroclastic flows have been observed in Tyres Ghaut, Gages Valley and behind Gages Mountain to the north. Many flows appear to start from a location high up on the north west side of the dome behind Gages Mountain, then split as they reach the "watershed" behind the mountain, leading to material spilling into both Gages Valley to the south and around to the north down a chute to the west of Tyre's Ghaut joining into Tyres Ghaut lower down. Many have been accompanied by ash venting. The most significant event began at about 15:24 (local time) on 4 January and resulted in simultaneous pyroclastic flows in Gages Valley and in Tyres Ghaut and an ash cloud, which reached an estimated 8,000 ft. (2,500 m). This ash had a reddish hue, suggesting mobilisation of older material. The flow in Tyres Ghaut was weak, and had limited run out (few hundred metres), however, the flow in Gages valley was much more energetic, and part of it spilled out of Gages Valley to the north across the plane towards Lees for about 500 m. The run out distance for the main part of the flow in Gages was around 4 km. This was the biggest single event during this current phase of north-westerly directed dome growth. To date flow run out distances in Tyres Ghaut have been limited to about 1.5 km. After dark incandescent rockfalls have been clearly visible on a sector of the dome extending from south of west (Chances Peak) to the north east above Farrell's plain, confirming active dome growth remains focused to the north west. Low-level gas and ash venting from a vent on the western side of the dome is ongoing, and has at times been audible as a low roaring or rumbling sound Fortunately the prevailing wind direction remains E-W and the occupied areas of Montserrat have been largely unaffected by ash fall. Seismic activity for the period has been relatively low, comparable with periods before the recent switch in the direction of dome growth, and dominated by rockfall signals. During the period the seismic network recorded 231 rockfall signals, 21 long-period rockfall signals, 22 long-period earthquakes, 3 volcano-tectonic earthquakes and 3 hybrid earthquakes. The seismic signals associated with pyroclastic flows and ash venting activity often exhibit small amplitudes and are therefore not always recorded across the entire monitoring network. Seismicity remains relatively low, and is dominated by rockfall signals and long period earthquakes - accepted as resulting from either surface or shallow (1-2 km) activity. The sulphur dioxide (SO2) flux rate during the period was low, ranging from a minimum of 85 tones per day (t/d) to a maximum of 262 (t/d), with an average of 152 t/d. Whilst gas and ash venting is visually extremely obvious (and occasionally audible), there is no reason why this should correspond to high sulphur dioxide emissions, volcanic gas emissions from the Soufrière Hills Volcano include water, carbon dioxide and hydrogen chloride also in significant quantities. Sulphur dioxide is probably the least abundant of these gases. The alert level stands at 4. Residents of Montserrat and visitors to the island are advised to tune into ZJB Radio 95.5 FM for up-to-date information on the volcano. Access to all areas south of the Belham Valley [excluding Isles Bay Hill] is now suspended. The daytime entry zone, comprising the top part of St. George's Hill, is closed. Access to all areas south of Richmond Hill, and south of Jack Boy Hill to Bramble airport and beyond is prohibited at all times. The maritime exclusion zone around the southern part of the island extends 4 km off shore from Spanish Point to Roches Yard on the east side of the volcano, 2 km offshore from O'Garras to Gingoes on the south-west, and 200 m offshore from Plymouth. In view of the level of volcanic activity, a review of the extent of the maritime exclusion zone offshore around Plymouth in progress, and extreme caution should be exercised in that area. For further explanations of the volcanic phenomena described, and information about the Soufrière Hills Volcano and the ongoing eruption, please look at the MVO website: http://www.mvo.ms <http://www.mvo.ms/> . ---------------------------------------------- Dr Vicky Hards Director Montserrat Volcano Observatory P.O. BOX 318 Flemmings Montserrat West Indies. Tel: 1-664-491-5647 FAX: 1-664-491-2423 Email: vicky@xxxxxx <mailto:vicky@xxxxxx> http://www.mvo.ms <http://www.mvo.ms/> ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
