Ruapehu - IGNS - Media Release V96/01

March 28 1996 (Thursday)
1500 NZST (UT +12)

Ruapehu Volcanic Activity

On Tuesday and Wednesday, 26 and 27 March research parties have been working in or around the summit crater. They have observed a very small island in the Crater Lake near its south-western shoreline. Observations were hindered by steam and fume emissions, but indicate that the island is the top of a small lava extrusion, which is presently emerging onto the floor of the crater. Observers have reported vigorous steam and gas emissions and sediment-laden geysering about the margins of this extrusion. Its visible extent, above lake level, is very small; estimated to be about 15m high and 20m across. The lake level remains about 80m below overflow and the temperature 50oC.

The extrusion process has been passive todate and is not clearly reflected in the parameters monitored at Ruapehu. In Figure 1 is plotted the peak seismic amplitude, sampled every 3 minutes. The spikes reflect the discrete high-frequency volcanic earthquakes which occur at rates of 20-60 per day. There has been an apparent increase in these since about day 56 (February 25). These are the type of earthquakes that could be expected to accompany an intrusion-extrusion. If this is so intrusive-extrusive activity has been occurring passively since late February, but until now the extrusion has been concealed beneath the lake.

Activity at Ruapehu volcano has been at a low level for some months, by comparison to September-October 1995, but has been higher than it was pre-September 1995. As a result of this we have maintained the Alert Level at 2 and stated that this should not necessarily be interpreted to mean either that the present eruption episode has ended or that there are no hazardous areas on the volcano. The possibility of isolated explosive eruptions occurring without useful warning signals has always been present.

The appearance of this island, which would appear to be the result of a process which has been ongoing for 4-5 weeks indicates that the eruption episode which began in 1995 is not yet over.

We advise that the Alert Level remains at Level 2

BJ Scott for CJN Wilson (Volcanology Programme Leader)