A potentially lethal mix of mud, acidic water and rocks tore down the slope of New Zealand's Mount Ruapehu on Sunday, emergency officials said, but there was no immediate threat to life. The mud flow - also known as a lahar - broke through a rubble wall atop the mountain's crater lake about 10:47 a.m. Sunday morning, triggering an early warning alarm, Horizon Regional Council said. Police and civil defence workers immediately closed roads and the nation's main trunk rail track near the southern base of the mountain on New Zealand's North Island.
Government-owned science company GNS Science is using new laser technology to accurately measure erosion rates of the tephra dam at Mt Ruapehu’s Crater Lake. Using a technique called terrestrial laser scanning, scientists have created a detailed three-dimensional image of the entire dam to improve the understanding of the way natural dams fail. The project is part of ongoing research on the dam by GNS Science, Massey University, Victoria University of Wellington, and the Department of Conservation. This project has been initiated and paid for by GNS Science. Data gathering at the Crater Lake involves using a tripod-mounted instrument to take laser measurements across the dam. Each survey collects about 1 million surveyed points at high resolution across the entire dam. The scientists are planning multiple surveys which will enable them to identify erosion rates between subsequent scans as well as pinpointing parts of the dam that are undergoing deformation.
A small eruption on Mount Ruapehu in central North Island, New Zealand last Wednesday night, 4th October, may have sent a water plume about 200 meters into the air, and created waves about six meters high in the volcanic lake.
"It would have been a geyser-type eruption. It would have domed up water in the lake and lifted it maybe a couple of hundred of meters high" - Brad Scott, Geological and Nuclear Sciences (GNS) coordinator of volcanic surveillance.
The eruption happened during a bad storm, which had hindered the confirmation of the eruption.
Ruapehu began erupting at least 250,000 years ago and is largely composed of andesite. In historic times, major eruptions have been about 50 years apart, occurring in 1895, 1945 and 1995-1996. Minor eruptions are frequent, with at least 60 occurring since 1945.