Montserrat Volcano Observatory Weekly Report for the period 8 - 15 August 2008 Lava extrusion has resumed at the Soufriere Hills Volcano on the western side of the lava dome. The rate of extrusion is low and seismic activity is low apart from rockfalls associated with the extrusion. Sulphur-dioxide flux remains at an elevated level. The first evidence of the new extrusion was on 8 August. Although the dome was obscured by cloud, a new channel of fresh rockfall material could be seen below the Gages Wall. One rockfall was observed in this channel, generating an ash cloud that drifted over populated areas to the north west. It was not possible to make any observations of the dome until 14 August, when the wind turned to the north making parts of the west side of the dome visible from St George's Hill. The explosion crater generated on 28 July was apparent, but it was almost completely filled with new lava. The lava had spilled over the lower, western, side of this crater generating the rockfalls below the Gages Wall. During a 30 minute period, several small rockfalls were observed, and heard, from St George's Hill. It is not possible to determine exactly when lava extrusion began. It could have been immediately after the 28 July explosion or there could have been a pause before extrusion started, as has happened before. In either case, the time taken for the lava to fill the explosion crater indicates that the rate of extrusion has been low, probably less than 0.1 cubic metre per second. The northerly winds on 14 August and on the morning of 15 August blew the gas plume over inhabited areas of Montserrat and the smell of volcanic gases was very noticeable at times. Seismic activity was relatively low this week. The MVO recorded 21 rockfalls, 12 long period, 2 hybrid and 2 volcano-tectonic events. Most of the rockfalls occurred between 11 and 15 August and are associated with the new lava extrusion. The average sulphur dioxide (SO2) flux for the week was 1016 tons per day (t/d) with a minimum of 364 t/d on August 10 and a maximum of 1791 t/d on August 13. These values are similar to the elevated values recorded last week following the explosion on 28 July. FTIR (Fourier Transform Infrared Spectroscopy) measurements on 8 August gave a value of 0.62. This is a significant increase on recent values, which have been around 0.4, and is consistent with slow dome growth. Extrusion is expected to continue, and an increase in the extrusion rate cannot be ruled out. As more material is extruded, the lava should form a new lobe on the western flank of the dome. The steepness of the dome in this area makes it very likely that, as the dome grows, rockfall activity will increase and that this could generate pyroclastic flows on the western flank of the volcano. The Hazard Level is 3. Additional information on the Soufrière Hills Volcano and the new Hazard Level System can be found at the MVO website: 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. ==============================================================
