Last week a Crater Lake sampling and gas flight were completed by GeoNet staff at Mt Ruapehu. Observations and data from these activities confirm the Crater Lake is still cooling, but at a slower rate and there is volcanic gas passing through the lake. The temperature of the summit Crater Lake is now 13 ºC. The observations from the gas flight and sampling indicate the vent(s) on the lake floor are open, allowing gas, steam and water to vent into the lake. These are typical conditions for Mt Ruapehu.
The volcanic alert level for Mt Ruapehu remains at Volcanic Alert Level 1 (minor volcanic unrest). The Aviation Colour Code also remains unchanged at Green.
The gas flight completed on August 10 recorded the volcanic gas at levels typical of low-background output for Mt Ruapehu. Convection was noted in the lake. On August 11 a Crater Lake sampling for gas and water was also completed. Up welling was again obvious in the lake and was outlined by sulphur slicks, which are frequently seen when the lake is convecting. The lake was a dark green-grey colour and was overflowing. There was a fairly strong sulphur smell near the lake. The lake temperature was measured at 12.6 ºC, consistent with the data logger observations. Today the data logger reports a temperature of 12.9 ºC.
The level of volcanic tremor which was elevated to moderate levels in May-June has declined and is now at typical background levels. Data available at present indicates the level of volcanic unrest at Mt Ruapehu is low.
GNS Science volcanologists continue to closely monitor Ruapehu through the GeoNet project.
Steve Sherburn Duty Volcanologist