alert bulletin: Sep 18 2008, 11:00 am - Ruapehu Volcano

Volcanic Alert Bulletin RUA-08/05 - Status report; Volcanic Alert Level remains at Level 1

Ruapehu is showing signs of entering a new heating cycle. Gas output, lake temperature and volcanic tremor have all shown reversals of recent trends. These demonstrate typical behaviour for Ruapehu. The Alert Level remains at Level 1.

Ongoing monitoring at Ruapehu, including a recent Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity, have shown changes in the last month. These changes indicate that the period of lake cooling and lower gas flux is over.

The Crater Lake temperature has now increased to 22 °C, up from 16 °C in August. This temperature change was accompanied by some volcanic tremor. From October 2007 to June 2008 the lake temperature ranged between 34 to 37 °C before declining to a low of 16 °C in August 2008. The airborne gas plume measurements have shown a similar trend with SO₂ and CO₂ gas emissions being high while the lake was hot, decreasing when the lake cooled and now increasing again. Cyclic activity in the Crater Lake is very common at Ruapehu.

These observations are consistent with the volcano-hydrothermal system now being more open to the Crater Lake. This type of volcano unrest should result in the lake temperature continuing to rise and the lake colour changing as sediments on the lake floor are disturbed by the increased gas flow into the lake. Ruapehu remains an active volcano and future eruptions may occur without warning.

The Volcanic Alert Level remains at Level 1 (departure from typical background surface activity, signs of unrest).

Brad Scott
Volcano Surveillance Co-ordinator