GNS Science announced the raising of the Alert Status at Mt. Ngauruhoe to Level 1 (some signs of unrest) via its Geonet website this afternoon.
The status change results from a significant change in the number and magnitude of low frequency earthquakes being recorded by seismographs around the mountain during the last three weeks.
Low frequency earthquakes usually indicate the movement of magmatic fluids such as magma (molten rock) or volcanic gases.
The Geonet release reported that the earthquakes could be occurring at a 4 km depth under the volcano, but further analysis is still being carried out. Scientists plan to deploy further seismographs and conduct gas sampling in the area near the mountain during the next week.
The release pointed out that the change in activity does not necessarily mean that an eruption is imminent.
Mt. Ngauruhoe is a young cone on the flanks of the more massive Mt. Tongariro and part of its history was covered briefly on this site in April.
An increase in the number of volcanic earthquakes near Mt. Tongariro was reported by GNS Science on the 5th of November last year. The increased activity continued until December 3rd when a magnitude 2.4 earthquake was followed by a series of very small earthquakes similar to, but more frequent than activity that had been observed there in the previous month. At the time, it was thought that the quakes were due to increased hydrothermal activity on the mountain. The increased earthquake activity then continued being reported in the Hazardwatch website listings until February 10th after which it ceased being mentioned.
Mt. Ngauruhoe re-joins 3 other volcanoes in New Zealand with an Alert Level of 1. They are: Raoul Island, White Island, and Mt. Ruapehu.