Ruapehu - IGNS - Science Alert Bulletin V95/14

25 September 1995
Ruapehu Crater Lake
 
Situation Summary
 
As of 17.00 the following information is available.
 
*    The intensity of volcanic tremor and accompanying eruptions decreased
at about 09.00 hours and remained low until 12.10.  At 12.10 hours,
vigorous activity with accompanying strong tremor re-commenced,
maintaining this up to the time of writing this report.
 
*    There is a  substantial eruption column from the volcano, with the
products of many moderate-sized individual explosions merging to form a
continuous plume.
 
*    An ash-bearing plume is drifting to the east for several tens of
kilometres, rising to heights of about 10 km.  Volcanic ash is being
deposited over the Desert Road and into the Kaimanawa Mountains.  The
Desert Road has been closed as a precautionary measure.
 
*    A substantial lahar is present in the Whangaehu valley.  As at 16.30
hours, the lahar was continuing to flow at the Tangiwai Bridge, with a
continuous high concentration of sediment.  Significant erosion of the
stream bank upstream of the Tangiwai road bridge is occurring, and the
situation is being monitored.
 
*    The activity in the last 30 hours has been episodic, with 2 periods
of increased activity, one on Sunday night/Monday morning, and a second
since Monday mid- day.  This latter period is not quite as vigorous as the
first, based on the available seismic data.
 
Conclusion and Alert Status
 
A substantial eruption involving new magma is continuing at Ruapehu.  In
the light of our observations and conditions around the mountain, and the
seismic activity over the past 4 hours, we would advise that the Alert
Level for Ruapehu remain at Level 4, and the situation will be reviewed on
Tuesday morning.
 
For further information contact:
Dr C J N Wilson, Programme Leader, Volcanology. Ph: (07) 374 8211; Fax (07)
374 8199