Ruapehu volcano (North Island, New Zealand) - Smithsonian / USGS Weekly Volcanic Activity Report for 4 May-10 May 2016 (New Activity / Unrest)

GeoNet reported that a volcanic earthquake swarm beneath Ruapehu's summit Crater Lake was detected during 25-26 April. This type of swarm has been uncommon at the volcano in recent years, when volcanic tremor has dominated the seismicity. In addition, the crater lake water temperature had been rising since late 2015, from 25 degrees Celsius to 40 degrees in the last half of April.
Similar temperature increases were detected in March 2011, April 2014, and February 2015.



In a 3 May notice GeoNet stated that the size and number of events in the swarm had decreased; a period of moderate volcanic tremor began at 1310 on 2 May and lasted about an hour. The lake temperature had peaked at 42 degrees, equal to the highest recorded temperature since 2011. At around 1400 on 7 May tourists on an overflight of the area observed vigorous steaming at the lake surface and upwelling bubbles.
The lake temperature rose further, to 44 degrees, establishing a new high since temperatures started to be recorded in 2000. The earthquake swarm had stopped, though the seismic network continued to record volcanic tremor. On 11 May GeoNet stated that recent visits to the lake confirmed increased gas emissions from the crater lake.
The lake temperature increased to 46 degrees and moderate levels of volcanic tremor continued. The Volcanic Alert Level was raised to 2 (moderate to heightened unrest) and the Aviation Colour Code was raised to Yellow.

Source: GeoNet
---
From: Global Volcanism Program, 2016. Report on Ruapehu. In: Mayberry, G (ed.), Weekly Volcanic Activity Report 4 May-10 May 2016. Smithsonian Institution and US Geological Survey.