A M 2.8 earthquake centered at Ruapehu was recorded on 4 October. Scientists visited the summit crater lake on 7 October and confirmed that a small hydrothermal eruption had occurred. The lake water level had risen 1 m since a previous measurement, and evidence suggested wave action up to 4-5 m above the surface of the lake. The lake temperature was 22.5°C, up from 15°C. Ruapehu remained at Volcanic Alert Level 1 (some signs of volcano unrest).

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