Nov 5 1998, 10:30 am - White Island Volcano

Summary

Minor eruptive activity recommenced at White Island about October 24 - 25, being strongest on Saturday (October 31) and Sunday (November 1). Very weak volcanic tremor accompanied those minor ash eruptions. A surveillance visit was made on Monday November 2 to assess the activity, conduct a deformation survey, and collect ash and gas samples. The results from that visit are reported below.

In summary, minor eruptive activity continues at White Island. The level of activity has varied with time, however the current activity is not sufficient to raise the Alert Level from 1.

Observations

The active vent at the base of the north-west wall of 1978/90 Crater has grown slightly since it formed in August. During our visit a very weakly ash-charged reddish-grey convecting plume was being emitted. Occasional yellowish hues were present in the plume, consistent with the periodic eruption (ie. mining) of hydrothermal sulphur from the vent. The maximum temperature measurement for the ash column was 451°C. The minor eruptive activity over the previous days had deposited up to 15 mm of fine dark grey ash at the crater rim. Examination of these ashes show no change from those erupted in the July-August eruptions. We conclude the current ash eruption is still occurring from a crusted-over magma body.

The ground deformation survey shows a consistent trend of minor deflation across the main crater floor, with the largest changes (20 - 30 mm) near the crater rim area. However, fumarole temperatures have increased nominally since August 31. Fumarole #1 is now 113°C (up from 101°C), is moderately dry, and has molten sulphur in the orifice (indicating temperatures in excess of 119°C in the vent). Donald Mound continues to discharge only low pressure steam from diffuse areas of steaming ground, and the cracks around Peg M continue to discharge steam close to boiling point. Maximum temperature at Noisy Nellie was 140°C (up from 126°C), whereas pressures are similar to those observed in August. Temperatures at 13a, now at 111°C, have also increased slightly from those in August (cf. 105°C). The plume from the island appears to carry a heavier SO₂ burden than observed in August.

Brad Scott
Volcano Surveillance Manager