alert bulletin: Jul 21 2008, 3:00 pm - Ruapehu Volcano

Volcanic Alert Bulletin* RUA-08/04 - Unrest declines; Volcanic Alert Level* remains at Level 1

Ruapehu is showing signs of a decline in the level of unrest. Gas output, lake temperatures and volcanic tremor have all declined. The volcano last erupted on September 25 2007.The Volcanic Alert Level remains at Level 1.

Ongoing monitoring at Ruapehu, including a Crater Lake visit to measure the lake temperature and collect water samples, data from airborne gas measurements and seismic activity, have shown declines in the recent measurements. This indicates that the current period of elevated unrest is passing.

The Crater Lake temperature has now dropped to around 23 to 25 °C, having ranged from 34 to 37 °C since October 2007. The latest measurement was 23.3 °C (July 15). The airborne gas plume measurements which had shown significant increases after April 2008 now show that SO₂ and CO₂ gas emissions have decreased to the typical background levels for Ruapehu.

Results from the Crater Lake chemistry are also indicative of cooling in the vent area. The slight increase in the level of volcanic tremor we previously reported has also declined to typical background levels.

These observations are consistent with the volcano-hydrothermal system now cooling. The current phase of volcano unrest appears to be over, however Ruapehu remains an active volcano. 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

* Previously known as Science Alert Bulletin and Scientific Alert Level.