Ruapehu - IGNS - Science Alert Bulletin V96/10

June 17 1996 (Monday) 1700 NZST (UT + 12)

Ruapehu Volcano

Update

A significant local eruption of Ruapehu volcano started this morning at
about 0700h. The level of activity was such that the Alert Level was
raised from Level 1 to Level 3.

Volcanic tremor at Ruapehu began to increase at around 0600 hr this
morning and continued to increase until about 1100h when it plateaued out
at levels similar to those during the October 11-12 1995 eruptions. By
about 1330h the level of volcanic tremor was starting to decline, and the
style of activity changed to discrete explosive events.  Observers near
the mountain reported loud detonations and windows shaking. About 1500h
the volcano started to erupt every 10-15 minutes, sending ash laden plumes
to several kilometres height, and continues to erupt in this style, but
appears to be declining at this time.

An over flight was made this afternoon as the more discrete ash eruptions
started to occur.  Observers can confirm a small lahar down the Whangaehu
catchment but no evidence for pyroclastic flows out of the summit crater
basin.

The attached plot shows the tremor levels as recorded at Dome and Chateau
seismographs during June 1996. The upper trace is Dome, the lower Chateau.
The plot is in universal time, hence is 12 hours out of phase with local
time. The plot ends at 1200h local time.  This plot shows how the seismic
activity has changed during the last month.

Light ashfalls have been experienced by much of the zone extending north
from the volcano to the Bay of Plenty coast. The margins have been at
Tauranga and Whakatane at the coast.

In summary, the volume of ash emission and seismic activity indicate the
eruption is similar in scale and type to the events on 11/12 October
1995.

BJ Scott for CJN Wilson  (Volcanology Programme Leader)

Plot of the amplitude of the volcanic tremor as recorded at Dome and
Chateau seismographs (Mt Ruapehu).