MVO report for the period midday 21st September to midday 28th September, 2007
By MVO
Fri, 28 Sep 2007, 11:27
Montserrat Volcano Observatory
Report for the period midday 21 September to midday 28 September 2007
Visual observations during the period have shown no changes to the dome structure and the pause in lava extrusion [and dome growth] continues. Nevertheless, whilst lava extrusion has ceased and the dome may not be actively growing, it remains as a large mass of partially molten lava capable of collapsing or exploding, although the likelihood of this decreases with time as no further lava extrusion occurs.
The occasional "roaring" sounds experienced are due to venting; heightened after rainfall as water permeates into the hotter interior of the dome resulting in steam venting. A southerly wind direction makes the venting more audible.
Overnight rainfall resulted in minor lahar (mudflow) activity in drainages around the volcano including the Belham River Valley in the early morning on 26 September.
Recorded seismic activity remained very low throughout the period. The seismic network recorded just 9 rockfall and 4 volcano-tectonic earthquakes.
The sulphur dioxide (SO2) flux rate was variable, ranging from a maximum of 507 tonnes per day (t/d) to a minimum of 58 t/d. The average flux rate for the period stood at 300 t/d, below the long-term average, which remains around 550 t/d.
Fourier Transform Infrared (FTIR) measurements on 25 September gave a hydrogen chloride to sulphur dioxide (HCL:SO2) ratio of 0.3, in line with recent measurements and previous periods when there was no active dome growth.
The alert level remained at 4.
Residents of Montserrat and visitors to the island are advised to tune into ZJB Radio 88.3 or 95.5 FM for up-to-date information on the volcano.
Access to all areas on the southern flanks of the Belham Valley east of the Belham Bridge and areas south are prohibited as is south of Jack Boy Hill to Bramble airport and beyond. 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 Sturge Park on the south-west (readers are referred to the updated risk map, available on the MVO website).
Additionally 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.
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@mvo.ms