New heating cycle to the Ruapehu's Crater Lake.

Ruapehu's Crater Lake - photo J.Shook

The crater lake of Mt Ruapehu, located on North Island / New Zealand has passed since the beginning of December 2014 from 15 ° C to over 40 ° C, according to the report of the GNS of January 30, 2015.

Measurements carried out in mid-January show changes in lake chemistry, particularly increased volcanic gas discharge, convection currents and discoloration: it went from blue-green to pale gray. All these changes indicate a new warming of the hydrothermal system beneath the summit lake.
 

The massif of Ruapehu - photo J.Shook

The volcanologist Brad Scott notes that "since 1950, the Crater lake's temperature ranges between 9 ° and 60 ° C. The lake is at a temperature higher than 37 ° C about 25% of the time, with an average of 30 ° C . The temperature cycles presented by the lake are not unusual ... since 2010, there are five heating cycles. {...} More rarely, the temperature rises above 40-42 ° C, which can give start to small steam eruptions. The current situation is very similar to the climax of heating episodes encountered between 1985 and 1996 ... if the temperature of the lake continues to increase, the largest eruptions could occur. "

Despite the risk of a phreatic eruption, the volcanic alert level remains at "1 / minor instability" and the aviation alert to "green".

Aerial view of the summit of Ruapehu September 26, 2007, days after a brief eruption. Crater Lake on the left, covered the top of ash and mud, and spawned a major lahar down the Whangaehu glacier (center) and another smaller one at the outlet of the lake in a gully (far left) - Photo courtesy of GeoNet 2007

Ruapehu is a complex stratovolcano, with an andesitic dominant, that have been built since 200,000 years in at least four episodes. This volcanic massif of 110km³ is elongated NNE-SSW and surrounded by a plain of volcaniclastic debris.

It was scored between 22,600 and 10,000 years ago by a series of sub-Plinian eruptions. Among summital vents and sides, only the Crater Lake is considered as active during historical time. It would be formed there are only 3,000 years, and has frequent explosive eruptions. The lahars produced by phreatic eruptions type of Crater lake are a danger to the ski area of the upper flanks and lower valleys.

Aerial view of Ruapehu - left in October 2002 - on the right, we see the trace of the lahar 25.03.2007 - Doc. NASA Terra ASTER. - Click for larger view.

Sources :

- GNS - bulletin d'alerte volcanique du 30 janvier 2015 - link

- Global Volcanism Program - Ruapehu