MVO report for the period January 04 to January 11, 2008
By MVO
Mon, 14 Jan 2008, 10:47
Montserrat Volcano Observatory
Report for the period 04 January to 11 January,2008
The helicopter support continues to be invaluable to the monitoring of the Soufrière Hills Volcano. An observation flight on 9 January once more confirmed that the dome morphology is almost identical to that of the previous reporting period. A horizontal zone of erosion on the eastern talus flank provides the main source of material for the small rockfalls which occasionally trigger the seismic network. One such rockfall created a small ash cloud on the morning of Monday 7.
The fumarolic activity continues on the northern and eastern flanks and observations from the Galway’s area to the south of the dome confirm active fumaroles in this zone, most of these fumaroles represent steam vents. The Gages Wall fumaroles are also still active one of which is the main source of the sulphur dioxide which can be distinguished by its distinctive bluish colour and represents a deeper source.
The recorded sulphur dioxide (SO2) flux rate for the reporting period ranged from a maximum of 706 tonnes per day (t/d) on 5 January to a minimum of 280 t/d on 10 January. The average flux rate for the period was 513 t/d. This figure continues the trend of a reduction in sulphur dioxide flux and is slightly lower than the long term average for the eruption of 550 t/d. Due to the positioning of the gas plume no Fourier Transform Infra Red (FTIR) HCl:SO2 flux ratio measurements were possible.
The seismic network recorded 8 volcano-tectonic earthquakes, 2 rockfall signals, 1 long period event and 1 long period rockfall.
The GPS data retrieved from the South Soufrière Hill installation on 3 January has now been processed with the other GPS positional data. The calculations demonstrate that the baseline lengths have had little or no change since November when the last calculations were made.
The pause in activity continues with no dome growth from lava extrusion. More thermal images taken from the helicopter and Galway’s Wall once more support this. It must be remembered that some areas of the interior of the dome will remain molten with the possibility of collapse or explosion remaining. But as the system cools without the introduction of fresh magma and the pause continues the likelihood of this is believed to decrease.
During heavy precipitation it must be remembered the potential hazard from lahar (or mudflow) in the drainage channels around the volcano remains.
The alert level remained at 4.
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’Garra’s to Sturge Park on the south-west (readers are referred to the updated risk map).
For further explanations of the volcanic phenomena described, and information about the Soufrière Hills Volcano and the ongoing eruption, please look at the rest of the MVO website. http://www.mvo.ms.
Mick Strutt
Director
Montserrat Volcano Observatory
Flemmings
Salem
Montserrat
Tel: 1 664 491 5647
FAX: 1-664-491-2423
e-mail: mick@mvo.ms; mhst@bgs.ac.uk