The seismicity during the period under review was generally low, although a period of hybrid events occurring every few minutes started at about 15:50 this afternoon and continues at present. A period of moderate amplitude, broadband tremor started at 20:30 on 11 January and continued until approximately 06:00 this morning, although it became intermittent after 02:00. A total of 5 earthquakes were located during the period under review, three at shallow depths beneath the Soufriere Hills volcano and the other two beneath St George's Hill and Harris at depths of about 3 km. Two events recorded at the Gages and Long Ground seismic stations were correlated with small ash falls to the west of the volcano. These events occurred at 10:26 and 11:22 this morning and probably represent a combination of the signals of rock avalanching and small explosions at the surface. A regional event occurred at 16:59 on 11 January approximately 240 km from Montserrat. This event had a magnitude of 3.8.
EDM measurements were made today on the White's Yard - Long Ground - Castle Peak triangle, and on the Gages Wall - Dagenham - Amersham triangle. No significant change within the errors of the technique was noted from previous occupations for either of the triangles.
Visual observations of the crater were made from the helicopter this morning. The major new spine first noted on 10 January has again grown considerably during the period. The event responsible for the ash-fall at approximately 10:30 this morning in the Plymouth area was witnessed by scientists from the helicopter. A small pyroclastic flow was generated by major rock fall from one of the areas of dome growth which may have been accompanied by some small explosions. Such events are likely to continue whilst dome growth is still occurring, and some may generate enough ash to reach the Plymouth area in small amounts.