Volcanic earthquake; rise in lake level; Alert Level remains at 1 - Jul 14 2009, 3:00 pm

 alert bulletin: Jul 14 2009, 3:00 pm - Ruapehu Volcano
Volcanic Alert Bulletin RUA-09/01 - Volcanic earthquake; rise in lake level; Alert Level remains at 1

At 6.30 pm Monday evening there was a small (magnitude 2) volcanic earthquake beneath Ruapehu’s crater lake.

As a result of a new research project measuring the temperature and level of the lake we observed a 15 cm jump in lake level following the volcanic earthquake. The crater lake temperature is unchanged at 20 °C.

The crater lake was examined by helicopter late Tuesday morning. Viewing conditions were very poor, but no obvious changes have occurred since the last visit on July 2. No eruption had occurred and the lake was overflowing.

Our preliminary interpretation is that the volcanic earthquake was followed by about 20 million litres (about 8 Olympic-sized swimming pools) of extra water moving into the lake from the hydrothermal system beneath it. A much larger rise in lake level followed a very small eruption in October 2006, so such phenomena are not unknown at Ruapehu. However, this is the first time we have been able to correlate such a small rise with a single volcanic earthquake.

Observations will continue as conditions allow.

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