Mt Ruapehu may be entering a new heating cycle.
The volcanic alert remains at one but the mountain's gas output, lake temperature and volcanic tremor have all shown reversals of recent trends, GNS Science volcano surveillance coordinator Brad Scott said.
He said the behaviour was typical for Mt Ruapehu and said ongoing monitoring showed the period of lake cooling and lower gas flux was over.
The crater lake temperature increased from 16degC in August to 22degC now.
The temperature change was accompanied by some volcanic tremor and increased gas emissions.
"Cyclic activity in the crater lake is very common at Ruapehu.
"Ruapehu remains an active volcano and future eruptions may occur without warning."
The level one volcanic alert means there has been a departures from typical background surface activity and/or signs of unrest.