Scientists make use of volcanic eruption lull

Ruapehu Bulletin, Volume 13, Issue 606, 3 October 1995, Page 1

Scientists make use of volcanic eruption lull

Mt Ruapehu remained relatively quiet over the 50 hours prior to Sunday 3.30pm but geoscientists with the Institute of Geological and Nuclear Sciences reported that they were maintaining a high level of research and monitoring. The Bulletin has been told from an unofficial source that there were three eruptions in the 24-hour period to midday yesterday, but that they were possibly steam only. The Bulletin has been unable to get more accurate up-to-date information from IGNS because they have decided to delete this newspaper from their media release list, for reasons unknown. However the following IGNS information and media releases were obtained from another source: As at Monday morning, 9.00am volcanic seismicity remained at near pre-eruption levels for most of the night. Some high frequency volcanic earthquakes had been recorded near the Dome. No eruption related earthquakes had been recorded since 1 .00am Saturday and no eruption activity received. The last lahar was at 8.40am on Friday, and the last explosive eruption at 1.00am Saturday, 30 September. The longest previous quiet period was 23 hours from Monday evening to Tuesday evening last week. On Sunday afternoon IGNS released the following: This last week has been the greatest departure from Ruapehu's known norms since 1945. Consequently it has provided the first opportunity for this generation of geoscientists to observe a large-scale eruption at Ruapehu. Several have experienced large eruptions at other volcanoes, but only small-scale events at Ruapehu. Dramatic window Such volcanic events offer a dramatic window on the inner Earth, and information gained during that time will give priceless data to help with establishing volcanic behaviour patterns and recognising similar patterns in

future. Three new research approaches are being tackled on Ruapehu to maximise the situation. First, a wider range of seismic equipment has been placed round the mountain to track depth and location of the points where the earthquakes originate. This will indicate the depths and directions of magma movement within and under the mountain. TurntoPage2

Scientists take advantage volcanic lull

FROMPAGEl Secondly, 1.5km of cable with geophones are being laid in an L-shape on the flanks of Ruapehu to study the seismic tremors. The scientists conducting this experiment are hoping strategic placement of this

sensitive equipment will refine the variations in tremor levels that are occurring, and accurately locate their source. The third plan for stepped-up monitoring involves checking for changes in the shape or slope of the ground surface on the flanks of the volcano. Many volcanoes deform or bulge when magma starts accumulating, moving round various pipes and chambers, or creating new pathways and reservoirs within the mountain. Targets for laser ranging measurements will be set up at three areas around the mountain so that any tilting and bulging can be measured from a safe distance. So far, however, there is little indication that Ruapehu is a tilt or a bulge type of volcano. It is unlikely to have a large eruption such as Mt Helen's, Pinatubo or Rabaul, where there was considerable deformation before the eruption. There has been no significant earth deformation recorded on Ruapehu as part of this eruption. Understanding how and why volcanoes erupt is the theme to most volcanological research, and active volcanoes need individual attention because they have many minor, and some major, differences in eruptive style and behaviours. New Zealand's incred-

ibly lively geological environment gives urgency to such work because of the social and economic downside to being caught uninformed or unprepared. The practical application of

this research is to give forecasts and assessments of the problems that a particular volcano may cause, so that plans can be made to diminish their effects. Constant and long term

monitoring is absolutely basic to discovering the background pattern of volcanic behaviour so that deviations and trends away from these known norms can be tracked.