Mount Ruapehu's alert level has raised from level one to level two.

The notification was issued today at 11.45am by Bay of Plenty Civil Defence emergency management group.

A view of Ruapehu South at 7am. Photo: GNS.

The aviation colour code has moved from green to yellow.

Duty volcanologist Geoff Kilgour says recent visits to the volcano have confirmed an increase in the output of volcanic gas from Mt Ruapehu's Crater Lake.

Moderate levels of volcanic tremor continue and the lake temperature measured by the outlet data logger is 45C.

'The increase in gas output, the high lake temperature and continued seismicity suggest that Ruapehu is at a higher level of volcanic unrest.”

As a result, GNS scientists revise the Volcanic Alert Level to Level 2 (moderate to heightened unrest). The Aviation Colour Code is also changed, from Green to Yellow, says Geoff.

'We made two monitoring visits to Mt Ruapehu yesterday, one was a gas flight to measure the gas output and the other was to sample the Crater Lake water and make additional ground based gas measurements.

'Volcanic gas measurements indicate an increase in the amount of both carbon dioxide and sulphur dioxide output. The ground based gas measurements were complimentary to the airborne data. '

Geoff says seismic activity at Mt Ruapehu is usually dominated by volcanic tremor. Since the volcanic earthquakes in late April, the seismicity has been dominated by volcanic tremor at varying levels.

'The level of tremor has increased but is not exceptional in terms of the last few years.”

The temperature of the Crater Lake as measured by a data logger near the outlet has been rising and since mid-April 2016, and has risen from 25C to 46C. For the last couple of days it has ranged between 45C and 46C.

Geoff says taken together the data now indicate more volcanic unrest at Mt Ruapehu. The increased gas output coupled with high heat flow and volcanic tremor imply a higher likelihood of activity.

'At this time these changes at Ruapehu are considered sufficient to change the Volcanic Alert Level. The volcanic alert level for Mt Ruapehu is now raised to Volcanic Alert Level 2 (moderate to heightened unrest). The Aviation Colour Code has also changed, from Green to Yellow.”

Geoff says GNS Science volcanologists continue to closely monitor Ruapehu through the GeoNet project.