Mount Ruapehu is experiencing an “uncommon style of small earthquakes”, GNS Science says. 

The volcano’s crater lake recently had a drop in temperature and the agency earlier this month observed minor earthquake activity it described in a statement today as “quite uncommon for Ruapehu”. 

The Volcanic Alert Level remains at 1 and the Aviation Colour Code at Green. 

“In early March 2024, we first observed an uncommon style of small earthquakes at Ruapehu. Subsequent re-examination of seismic data has revealed those earthquakes commenced at least as early as mid-February. 

“The earthquakes are small and were initially difficult to identify without careful examination of the data as they are uncommon at Ruapehu and only the larger examples are detected by our automatic systems,” the statement said. 

“Over the last month, we have seen a maximum of six of these earthquakes a day, and on many days none at all.” 

GNS said each earthquake consisted of up to about 10 minutes of ground shaking and was composed of “a number of similar sub-events”. 

“While we are able to determine a location for some of the larger examples, the small size and style of the activity means our locations, especially depth, are quite uncertain. 

“However, as they are recorded only by monitoring stations on the upper part of the volcano, we speculate that they originate near the summit area of the volcano within a few kilometres’ depth beneath the surface.” 

As the earthquakes did not typically last more than 10 minutes, they didn’t constitute volcanic tremor, GNS said. 

The earthquakes were also quite different in appearance from volcanic tremor traditionally seen at Ruapehu. 

“While the earthquakes represent something new at Ruapehu, and we are working on understanding the details of the processes driving them, they are not thought to pose any concerns for eruptive activity. 

“Other monitored parameters have shown no recent changes. The temperature of Te Wai ā-moe (Crater Lake) is now relatively stable at about 24C, recent observations of the lake recognised nothing unusual, gas emissions from Ruapehu remain moderate.”