Ruapehu - IGNS - Media Release V95/23

29 September 1995
16.30 hours
Ruapehu Crater Lake

Situation Summary

As of 16.30h the following new information is available.

*    Over night the levels of volcanic tremor has varied in a pattern
similar to  the last six days.  Strong  tremor dominated from 1400h to
2200h on 28 September. From 2200h to 1200h today  the level was lower, but
still elevated above pre-eruption levels (eruptive activity at the volcano
was relatively quiet through the night, but clearly activity is still
continuing).  Since 1200h today the tremor level has risen again and
remains high at this time.

*    A large volcanic  earthquake (M3.2) was recorded at 0841h (today)
producing an eruption column to about 6000m, a lahar down the Whangaehu
catchment (observed) and ashfall south of the volcano.

*    Several discrete volcanic earthquakes have occurred since 1200h,
coincident with the increase in volcanic tremor at that time. Several
eruption plumes have been reported.

*    Institute staff were unable to conduct an overflight this morning,
due to weather conditions, but are attempting to at this time. Views
obtained late yesterday (28 September) confirm crater lake is still
present but it is considerably smaller than  previously.  Several steaming
blocky islets could be observed through the lake surface indicating much
of the lake may be relatively shallow. There is still sufficient water to
produce lahars, as was demonstrated by the 0841h eruption this morning.

*    Institute staff are maintaining a 24hr watch on the seismicity, and
are checking ground deformation networks this afternoon. A team of
seismologists from Wellington have installed 9 portable seismographs
around the volcano, so that more data can be collected to further our
understanding of the processes operating at depth bellow the volcano. The
scientists can detect the difference between explosion earthquakes and the
more normal rock shearing ones. Data obtained on wednesday included 14 of
these events.  Other Institute scientist are currently analysing ash,
leachate and scoria samples collected in the last few days.

*    The Alert Level for Ruapehu remains at Level 4.  

BJ Scott for; 
Dr C J N Wilson, Programme Leader, Volcanology.