Report on Soufriere Hills (United Kingdom) — December 2003
Bulletin of the Global Volcanism Network, vol. 28, no. 12 (December 2003)
Managing Editor: Richard Wunderman.
Soufriere Hills (United Kingdom) Dome growth ceased after July 2003 and remained absent 6 months later
Please cite this report as:
Global Volcanism Program, 2003. Report on Soufriere Hills (United Kingdom) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 28:12. Smithsonian Institution.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Weekly summaries of seismic activity at Soufrière Hills for the period 7 November 2003 to 16 January 2004 are given in table 51. During the week of 14 to 21 November a prominent swarm of hybrid earthquakes lasted for three days. Good views and surveys of the dome during this week confirmed that no growth or changes took place. On 9 December and on 31 December 2003 swarms of small hybrid earthquakes were observed on the drum records, but most of the events were too small to be recorded on the network. Visual observations confirmed that no new dome growth has occurred in the crater since July 2003, although there has been some slumping of old dome material from the crater walls, and degradation of the wall rocks by steam activity.
|Date||Rockfall||Long-period / Rockfall||Long-period||Hybrid||Volcano-tectonic|
|07 Nov-13 Nov 2003||1||3||1||36||--|
|14 Nov-20 Nov 2003||7||--||13||287||4|
|21 Nov-27 Nov 2003||5||--||1||50||1|
|28 Nov-04 Dec 2003||1||--||--||12||0|
|05 Dec-11 Dec 2003||--||--||4||13||--|
|12 Dec-18 Dec 2003||2||--||--||12||--|
|19 Dec-25 Dec 2003||1||--||--||2||--|
|26 Dec-01 Jan 2004||2||--||--||9||--|
|02 Jan-08 Jan 2004||2||--||--||2||--|
|09 Jan-15 Jan 2004||5||--||1||18||--|
Table 52 shows a summary of the gas emissions (mainly sulfur dioxide, but one HCl estimate for 18 December). Instrument problems or unfavorable wind directions disrupted measurements for a number of days during the report interval (dashed lines).
|Date||SO2 emissions (tons/day)||HCI emissions (tons/day)|
|07 Nov-13 Nov 2003||200-800||--|
|14 Nov-21 Nov 2003||260-450||--|
|21 Nov-27 Nov 2003||500||--|
|28 Nov-04 Dec 2003||300-600||--|
|05 Dec-11 Dec 2003||300-900||--|
|12 Dec-18 Dec 2003||500-3,600||1,260 (HCl:SO2 = 0.35)|
|19 Dec-25 Dec 2003||--||--|
|26 Dec-01 Jan 2004||500||--|
|02 Jan-08 Jan 2004||300||--|
|09 Jan-15 Jan 2004||200-590||--|
Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.
Information Contacts: Gill Norton, Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvo.ms/).