September 2016 – NEW ZEALAND – After reaching record-low temperatures in August, the volcano’s closely-monitored crater lake has started to heat up very quickly since 2 September, Geonet reported. Ruapehu’s Crater Lake displays temperatures that follow periodic cooling and heating cycles that range between about 15 and 40 °C. In mid August, a record-low of 12 °C was measured, but New Zealand scientists have detected a rapid increase in temperature over the past days, along with increased seismic activity inside the volcano.
The highest-ever temperature of the lake, since it had reformed in 1999-2000 was 46°C on 11 May 2016. This peak was also accompanied by volcanic tremor and an increase in gas emissions. GNS Science back then raised the alert level to Level 2, but lowered it back to Level 1 in early July, when degassing and seismic activity became less. The heating and cooling cycles of Ruapehu’s crater lake are not completely understood, but caused by a mix of volcano and geothermal processes; a heating period usually indicates a period of higher volcanic unrest which includes a higher possibility of a new eruption to occur. For now, the alert level is not raised as the current signs of unrest are weak.
The last eruption of Ruapehu was a small explosive event in 2007, but larger eruptions such as those in 1995 and 1996 are a serious threat to the skiing areas of the volcano and its surroundings. One of the main hazards of a significant eruption are lahars – devastating mud floods from the crater lake and from melting ice / snow. –Volcano Discovery