Saturday, October 07, 2006
Ruahepu volcano shows signs of activity
The 10.30pm event was first thought to be an eruption, but was later described as a moderate volcanic earthquake by Department of Conservation (DoC) scientists.
The damaging of a DoC monitoring sensor indicated there may have been some sort of eruption.
Scientists now have to wait until the weather clears – possibly at the weekend – before they can determine whether there was an eruption on the mountain or not.
The crater basin has been placed on high risk warning, while the Whangaehu, Mangaturuturu and Whakapapaiti valleys are at medium risk.
DoC conservancy advisory scientist Dr Harry Keys said scientists from the Institute of Geological and Nuclear Sciences/GeoNet accompanied them on an aerial investigation of the crater to see if the lake was surrounded by black snow.
However, poor weather prevented any view, he said.
“We then travelled by road around to the Desert Rd and were able to inspect the Whangaehu River at one point. We found no sign of a lahar having travelled down the river.
Indications from the monitoring equipment are that any eruption, if there was one, was likely to have been small and any associated lahar too small to be detected off the mountain.”
The Eastern Ruapehu Lahar Alarm and Warning System (ERLAWS) detected the event, he said.
Dave Wakelin, of DoC, said yesterday the lahar, a gas build-up that threw a volume of water, was a normal occurrence.
Wednesday’s event was a “good practice for the main event”, which was expected either this summer or next.
Although the latest eruption was not as serious as in 1995-96, it was significant enough to set off the sensors. The main point of concern on the lahar’s trail down the Whangaehu was at Tangiwai.
Because material dropped out and settled in the Tangiwai area during that event, the riverbed was raised by two metres.
A road and rail bridge was also built and an alarm system installed last year.
Mr Wakelin said as that lahars worked opposite to floods, the effect on the Whanganui River would be minimal.
“Lahars are back-to-front of floods. It releases the further it travels from the mountain and the less it becomes.”
GNS Science volcanologist Steve Sherburn said the crater was “very quiet all day” yesterday and scientists accepted they would just have to sit and wait for the weather to clear before they could determine if there had been an eruption.
But if there was one, he agreed with Mr Keys that it would have been small.
The scientists needed proof before raising the alarm level to 2.
Although there had been earthquakes in the region lately they were not always associated with eruptions.
“Only some of them. That’s what makes it a little bit difficult. If it was a one-to-one relationship it would be fine. We’ll just have to sit tight and see if the volcano does anything over the next few days.”
Wednesday night’s activity wasn’t exciting enough for Whangaehu Beach Rd resident Yvonne Cavanagh to know about it.
When the Chronicle called it was the first she’d heard of any activity, she said.
The Cavanaghs’ property is about 90 metres from the river and about 8kms from the Tasman Sea.
The closing of the Whakapapa and Turoa skifields yesterday was not because of the eruption, rather the gusty winds and “very cold” conditions.