Increasing temperatures in the Mount Ruapehu crater lake, Te Wai ā-moe and an increase in volcanic tremors, are seen as part of the normal heating cycle, by volcanologists at GNS Science.

The alert level remains at 1, says duty volcanologist Geoff Kilgour.

The increasing lake temperature and volcanic tremor level is a characteristic feature of a heating cycle and represents the increased flow of hydrothermal fluids into the lake, says Geoff.

'Previous heating cycles have shown this increased tremor to last for days to weeks.”

Scientists intend visiting the lake this week to collect water and gas samples,weather permitting.

Te Wai ā-moe has a clear temperature cycle observed since 2003. During these cycles, the temperature ranges between about 12 and 40 °C over a period of about 12 months.

In February scientists described how the relatively long-period of elevated temperature of Te Wai ā-moe was coming to an end. During that period, the lake reached 38°C.

'We expected the lake to then cool as it has done many times before,” says Geoff. 'Over the past two months, the lake has indeed cooled to about 20 °C where it remained at this low temperature until Tuesday last week, when the lake starting heating again at a rate of around 1 °C per day. 'Following previous heating cycles, we expect the lake to continue heating for the coming weeks.”

Volcanologists don't see any signs of increased unrest.

'Current observations are consistent with minor unrest behaviour and because of this, we remain at Volcanic Alert Level 1 and the Aviation Colour Code stays at Green,” says Geoff.

While the alert level remains at 1, it is a useful reminder that eruptions can occur with little or no warning, says Geoff. GNS Science continues to closely monitor Mt Ruapehu and the other active volcanoes.