Ruapehu eruption like ‘Groundhog Day’

Dr Shane Cronin, head of the Volcanic Risk Solutions Group
Dr Shane Cronin, head of the Volcanic Risk Solutions Group

Massey University volcanologist Dr Shane Cronin, head of the Volcanic Risk Solutions Group, says the latest eruption and lahar on Mt Ruapehu is just like the September 1995 eruption.

“It’s like Groundhog Day. It’s just like the eruption in 1995. It’s quite spectacular. There are tonnes of black material around the Crater Lake. This seems to be made up of crater lake water, freshly erupted rock and rock from older eruptions. There has been a snow slurry lahar, which has flowed down the Whangaehu valley side of the mountain.”

Dr Cronin and his students from the Institute of Natural Resources drove to the Central Plateau on Tuesday night as soon as he heard about the eruption and spent the night camped by a lahar monitoring station at the base of Mt Ruapehu. They are now downloading data from monitoring instruments across the mountain, collecting samples and data and measuring the flow of the lahar around the lake. The instruments were purchased in December as part of a $720,000 Marsden Fund project led by Dr Cronin and Dr Vern Manville from the Institute of Geological and Nuclear Sciences (GNS).

“Our efforts yesterday included surveying precisely the levels of the lahars down the Whangaehu channel. The lahar deposits are an unusual mix of snow, mud and rock – like in ’95. There were at least three flows down the valley and our instruments installed for the Marsden Fund research project (on the March 2007 flow) seem all to have worked in capturing the flows as they passed.

He says the Whangaehu lahars were probably in total only about 15 per cent of the size of the March 18 lahar and were more or less confined to the upper mountain.

Eleven staff and students from the volcanic response group studied the lahar yesterday with 10 staying on today to concentrate on the northern flanks of the mountain, near the ski field, as well as working on more details of the Whangaehu lahars.

Dr Cronin says the technique used to gather information about the internal dynamics of the lahar, using seismometers, will be used to enhance predictive models being developed by the group. Dr Cronin says the difference between the lahar earlier this year and yesterday’s event is that this lahar was caused by an eruption, rather than a breaching of the Crater Lake wall. Because the event was eruption-related, he says, the early warning systems may not have measured the event accurately and he is hoping the monitoring equipment, still on the mountain after the March event, will prove to be more reliable.

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