Jul 21 1996, 11:30 am - Ruapehu Volcano

Sustained, moderate volcanic activity at Ruapehu has continued overnight. The pattern of seismicity reported for yesterday afternoon (discrete events at a rate of 2 - 7 per hour) changed between 18:30 and 19:00 into more continuous sustained tremor with fewer, smaller discrete events. From about 08:30, the continuous tremor levels have diminished and large, discrete events have recommenced, in similar fashion to yesterday afternoon.

Observations by an Institute staff member from an overflight, together with aircraft reports show that the ongoing discrete explosions are sending up individual plumes to a maximum of 14,000 feet, and that ash is being blown to the east-south-east at altitudes of 10,000 - 12,000 feet (3 - 4 km). The cloud top is at 20,000 feet (6 km), and no ash plumes have been observed to penetrate this level, unlike yesterday. The observed plumes were reported as being a brown colour, clearly were ash-bearing, but not ash rich, and only minor amounts of ash fall appeared to be occurring. Further visual observations were hampered by cloud, and this situation is anticipated to continue for the rest of today.

The Alert Level remains at 3.

Colin Wilson
Volcanology Programme Leader