Cooling of the hydrothermal system at Mt. Ruapehu has ceased and the volcano appears to have entered another cycle of heating.
GNS Science issued an alert bulletin for Mt. Ruapehu yesterday, the 18th of September 2008, reporting that the central North Island volcano’s crater lake had commenced heating and that volcanic gas output had increased.
The volcano’s crater lake, which had hovered at temperatures ranging between 34 ºC and 37 ºC during the period from October 2007 to June 2008, had fallen to 23.3 ºC on July 15th and then declined to 16 ºC in August. During the early part of September, the crater lake began heating again and is now at 22 ºC.
Sulphur dioxide and carbon dioxide gas levels, which had shown significant increases and were ten times the normal levels on June 12th, had reduced to normal background levels by August. However, recent measurements show that sulphur dioxide and carbon dioxide levels in the plume above the volcano have again increased.
Volcanic tremor, which had been at a slightly increased level, had also declined to typical background levels for the volcano during August. But, as the crater lake heated during early September, volcanic tremor accompanied the change.
The bulletin concluded that the volcano shows signs of entering a new heating cycle. Such cyclic activity in the crater lake is very common, and indicates that the lake is now more open to the volcano-hydrothermal system. It is expected that the lake temperature will continue to rise while disturbance of lake-bed sediments caused by gas flows will cause the lake to change colour.
Even though heating and cooling cycles are normal for the crater lake at Mt. Ruapehu, the bulletin points out that it is an active volcano and that future eruptions could occur without warning.
[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST.]