The lake reached a recent temperature high of 43 °C on 5 September marking the peak of the current heating cycle. For much of August the lake temperature rose at about 1 °C per day, starting from a low 23 °C, reaching the peak of 43 °C. Calculations indicate that around 600 MW of heat energy was needed to heat the lake, being about the same as the heat required to generate electricity from one of our geothermal power stations. The lake temperature is now 39 °C.

The post 1995/1996 Crater Lake displays temperatures that typically range between about 16 and 38 °C. In early August, we reported on the variations in the lake temperature. The lake had cooled to a low of 19 °C at that time. GeoNet obtains temperatures from the lake using a data logger with a temperature sensor in the lake and communications via a satellite link. In the August story, we discussed the variations of the lake temperature. An analysis of the lake temperature data since 2009 when we installed a datalogger shows that for 5% of the time it is warmer than 38 °C and another 5% it is cooler than 16 °C. The median temperature is 24 °C. Looking at the longer-term Crater Lake temperature data, collected from lake visits since 1950, the behaviour is similar.

The heating and cooling cycles are controlled by a mix of volcanic and geothermal processes. The results of the lake sampling in mid-August reflected the heating. Further sampling and visits to the Crater Lake are planned as the weather allows, being part of the standard GeoNet monitoring programme for Mt Ruapehu.