On 5 March, GeoNet reported that monitoring of the Ruapehu Crater Lake showed that temperatures at depth remained above background levels but had started a declining trend. Gas data from January and February showed emission rates of 15-25 tonnes per day of sulfur dioxide and around 650 tonnes per day carbon dioxide; these are within the usual range of emissions measured at Ruapehu. Seismicity remained low, characterized by weak volcanic tremor and some shallow earthquakes. Areas of discoloration in the lake, sometimes observed during the previous few weeks, are relatively common and thought to reflect internal lake convection processes. Scientists speculated that there was a partial blockage between the deep and shallow systems causing the lake temperature to remain steady; the relatively low temperature of Crater Lake, 22-25°C since March 2012, is one of the longest periods of low lake temperatures recorded. The Volcanic Alert Level remained at 1 (signs of volcano unrest) and the Aviation Colour Code remained at Yellow.

Geological Summary. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the NW-flank Murimoto debris-avalanche deposit. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. The broad summait area and flank contain at least six vents active during the Holocene. Frequent mild-to-moderate explosive eruptions have been recorded from the Te Wai a-Moe (Crater Lake) vent, and tephra characteristics suggest that the crater lake may have formed as recently as 3,000 years ago. Lahars resulting from phreatic eruptions at the summit crater lake are a hazard to a ski area on the upper flanks and lower river valleys.

Source: GeoNet