alert bulletin: Sept 28 2007, 4:00 pm - Ruapehu Volcano

Science Alert Bulletin RUA-07/05 - Eruption from Ruapehu: Science Alert Level remains at Level 2, updated observations

Scientists were able to briefly visit the crater lake this morning to collect water samples from the lake. The lake temperature is 19 °C, up from 13 °C as measured in August. 19 °C is still considered to be cool for the crater lake. There are several distinct up-welling areas visible over the northern vent with gas coming through them. The southern vent has a small up-welling associated with it indicating that it is not completely blocked. The lake level appears to have risen slightly from Thursday’s observations, which is consistent with heating and melt water inflows following the eruption.

A gas monitoring flight was also conducted this morning to measure any gas that may be associated with the eruption. Preliminary results indicate that only small amounts of SO₂ gas are present (~13 tonnes/day). No other volcanic gases were detected.

Indications from further analysis of the geological and seismic data are that the blast had a strong directionality to it. Most of the erupted material was directed northward towards the Whakapapa ski field, over the summit plateau.

We cannot rule out the likelihood of a future eruption and lahars at Mt Ruapehu in the next few weeks and as such people should follow Department of Conservation guidelines for access to the mountain. Any future eruption may also be strongly directional towards the summit plateau and hence the risk for that area remains high.

So far all evidence indicates that the eruption was hydrothermal in nature with no involvement of magmatic material.

The alert level remains at 2 (minor eruptive activity) and will be re-assessed on a daily basis.

Further observations and images are available.

Craig Miller
Duty Volcanologist