Montserrat Volcano Observatory

Daily Report
Report for the period 16:00 17 September
to 16:00 18 September 1996

Volcanic activity at the Soufriere Hills volcano during this reporting period reached the highest level yet during the current eruption. Volcanic-tectonic earthquakes, large rockfalls and pyroclastic flows continue to be the most common seismic signals.

There were 77 rockfalls, 4 volcano-tectonic earthquakes, 1 long period earthquake, 1 hybrid event and 1 teleseismic recorded during the 24-hour reporting period, a significant reduction in seismicity compared to yesterday. The continuous period of rockfall and pyroclastic flow activity which ended the reporting period yesterday continued up until 20:30 last night (17 September). This was followed by a brief period of lower activity before an abrupt, small explosive eruption occurred at about 23:42 local time (03:42 GMT). This explosive event lasted for about 48 minutes, with saturation on all stations for this period. Activity at the volcano returned to background level for the remainder of the reporting period with just a few small rockfalls and volcano-tectonic earthquakes being recorded.

Reports and visual observations by MVO staff through the night suggested that an eruption column was sustained for a short period of time, depositing gravel-sized material of both pumiceous and dense nature in areas across the central corridor and in the Cork Hill, Richmond Hill and Foxes Bay areas. All ash erupted during the night, either from the pyroclastic flows or from the explosive phase, was blown westwards over Plymouth and Richmond Hill, and both of these areas received heavy ashfall. According to reports from the NOAA Satellite Analysis Branch, the ash column attained a height of 37,000 ft and caused the closure of the airport in Guadeloupe.

Overnight observations of burning property in the Long Ground area were confirmed during an early morning and late evening helicopter flight. These properties were set alight by large hot blocks of dome rock which were blasted eastwards from the summit dome. This blasted material covers the areas west of Long Ground into the Hermitage area, but is not present on any of the other flanks of the volcano. More than half of the houses in Long Ground were impacted by blocks falling through roofs, at least seven houses were completely burnt. Damage caused by these projectiles was confined to this area only. The Tar River Estate House has been destroyed by a pyroclastic flow with only the brick walls still upstanding.

Although no clear views of the dome area have yet been obtained, it appears that the major collapse scar is on the eastern flank of the dome, with the scar cutting deep into the old Castle Peak Dome. Some material has been eroded from Castle Peak also and some deposition of material has occurred in the Tar River valley. The delta at the mouth of the Tar River valley has been enlarged again, and the valley itself is now totally devoid of vegetation.

No EDM measurements were completed today due to low cloud cover over the volcano. The early morning helicopter flight revealed that the Castle Peak reflector was destroyed by the overnight activity. GPS measurements were made today on the large network which straddles the entire volcano; the results of these measurements are currently being processed.

Large amounts of ash and gravel sized pumiceous material was generated in several areas along the flanks of the volcano today. Driving conditions may be hazardous in some areas and drivers are urged to exercise extreme caution and give due consideration for other road. All indications are that the period of heightened activity which began at 11:45 last night (17 September) has subsided. Pyroclastic flows which occurred during the early morning was confined to the Tar River valley and its immediate environs and it is expected that this would continue. Areas affected by associated ashfalls will depend on the direction and strength of the wind at the time. Dust masks should be worn at all times in ashy environments.

The extensive damage which occurred in the Long Ground area today clearly demonstrates that the Tar River Valley, Long Ground village and surrounding areas are now extremely hazardous, and should not be entered under any circumstances. We urge individuals who persist in ignoring this advice to think very seriously before making trips to these potentially deadly zones.

At a press conference this evening the Governor H.E. Frank Savage congratulated the Emergency Response Mechanism for activating successfully their plan of action to remove people from the unsafe zone. During the course of the night, everyone was relocated to the safe zone in the north of the island. At this same press conference residents of Cork Hill and surrounding areas were advised that it is safe to return home tonight.

Montserrat Volcano Observatory