On 28 June GeoNet reported that it had been 10 days since the last notable tremor at Ruapehu and the level remained weak. Lake water temperatures declined to 21 degrees Celsius on 14 June from a high of 40 degrees Celsius recorded in early May; temperatures had increased to 25 degrees Celsius during the previous two weeks. Gas emissions continued to fluctuate based on data collected during overflights and were about 10% less on 23 June than on 13 May, though the sulfur dioxide rate during 24-25 June was comparable to those recorded in mid-May, based on gas measuring equipment recently installed at the volcano. The emission, water temperature and seismic data together indicated continuing moderate levels of unrest. The Volcanic Alert Level remained at 2 (on a scale from 0-5) and the Aviation Color 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