On 4 July GeoNet reported that analysis of water from Ruapehu’s cater lake confirmed that there is no interaction between magma and the hydrothermal system that drives composition, level, and temperature of the lake. New magma that had intruded over the previous 2-3 months had stopped moving. Tremor had declined to near background levels and gas emission rates were generally low. The lake water temperature had decreased by one degree and stabilized at 24 degrees Celsius. The Volcanic Alert Level was lowered to 1 (on a scale from 0-5) and the Aviation Color Code was lowered to Green (the lowest level on a four-color scale).

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