Lava extrusion has continued throughout the reporting period. There is now a broad spine in the southern summit area of the dome. Rockfalls and small pyroclastic flows have occurred across a sector from the west to the southeast of the lava dome and occasional rockfalls have been seen on the north side of the dome. The dome has been cloud-covered through much of the reporting period but clear weather on 18 May allowed a survey of the southern half of the dome to be carried out using a terrestrial laser scanner (LiDAR - on loan from the British Geological Survey). This showed that the summit of the dome has reached a height of 1006m (3270ft), this is 83m (270ft) higher than Chances Peak.
During the reporting period, seismicity was dominated by rockfall activity with an increase in long period seismicity. The seismic network recorded 753 rockfall signals, 208 long period-rockfall signals and 130 long period earthquakes, 7 hybrid earthquakes and 1 volcanotectonic earthquake.
Measurements of the sulphur dioxide flux were taken on two days during the reporting period and ranged from 504 tonnes per day (t/d) on 14 May to 844 t/d on 16 May. The average for the period was 674 t/d.
Hydrogen chloride to sulphur dioxide ratios of 3.89 to 5.89 were measured on four days during the reporting period. The ratios have been above 3 since January 2006 and are probably a reflection of the high lava extrusion rates.