The pattern of volcanic activity established during the past few weeks was interrupted by the occurrence of a moderate size pyroclastic flow which was discharged down the Tar River valley at 7:55 am this morning. This event lasted about ten minutes after which the activity returned to the background level. Throughout the rest of the reporting period rockfalls and some long-period earthquakes dominated.
A total of 91 rockfalls and 33 long period earthquakes were recorded by the seismic network. There were also 22 small hybrid and 1 volcano-tectonic earthquakes. The number of long-period earthquakes remain at a higher level than anytime in the last year. These types of earthquakes are thought to be due to gas movement near the surface of the lava dome. There has also been a 20% increase in the frequency of rockfall activity since Saturday May 10.
The pyroclastic flow of this morning highlighted the activity during the period under review. Due to restricted visibility the location on the dome from which the flow originated could not be seen clearly. The flow however eroded a notch in the talus of the dome and traveled down the Tar River valley to the delta where it fanned out. An ash plume was generated which rose rapidly to an altitude of approximately 9000 feet, mushroomed , and was swept towards the south-west by the prevailing winds. A generous quantity of ash fell along the narrow footprint of the travel path of the plume, affecting mainly the areas of Lovers Lane, Richmond Hill, Foxes Bay and Garibaldi Hill
Low cloud cover and extremely ashy conditions prevented detailed viewing of the summit area and inhibited the regular field the surveys today. Vigorous steaming could be seen emanating from the vicinity of the location where the flow originated.
The volcano remains dangerous, and only essential visits should be made to the evacuated zone. People should wear masks when in the ashy areas. The Tar River and White River valleys are extremely dangerous, and should not be entered under any circumstances.