Ruapehu - IGNS - Science Alert Bulletin V95/13

25 September 1995
Ruapehu Crater Lake
 
Situation Summary
 
As of 09.30 the following information is available.
 
*    About 12 midnight the frequency of volcanic earthquakes increased
significantly.  Strong tremor was recorded at approximately twice the
intensity of activity yesterday until ca. 9.00 and thereafter declined
slightly, and seismic signals reflecting individual explosions merged to
form a confused signal
 
*    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 plume is drifting to the east for several tens of kilometres,
rising to heights of about 10 km.  Ash is being deposited over the Desert
Road and into the Kaimanawa Mountains
 
*    A substantial lahar is presently flowing down the Whangaehu valley,
and the situation is being monitored by DoC, ECNZ, and NZ Rail.  The lahar
is up to level 4 on the NZ Rail monitoring system.  The lahar has declined
in size since 09.00 hours.
 
Conclusion and Alert Status
 
A substantial eruption involving new magma is under way at Ruapehu.  In
the light of our observations and conditions around the mountain, and the
marked escalation in seismic activity, we would advise that the Alert
Level for Ruapehu be raised to Level 4, effective now.
 
For further information contact:
Dr C J N Wilson,  Programme Leader, Volcanology
Ph: (07) 374 8211; Fax (07) 374 8199