GNS has raised the alert level of Ruapehu to Level 2 after a combination of crater lake heating, seismicity and gas emissions.
Crater lake heating to 43 °C
The crater lake regularly goes through a heating and cooling cycle. Since 2003, the lake’s temperature has risen above 40 °C six times before cooling to approx 15 °C. Generally, at temperatures exceeding 40 °C we start to see low thermal anomalies on MODIS data (two were recorded this month). Previous eruptions have occurred both when the lake has been hotter and cooler, but are more likely when hot.
If the increased temperature was the only anomaly, it’s unlikely GNS would have revised the Alert Level up.
Update: The lava is now at 41 °C and based on past trends, will likely continue to cool.
Increased Volcanic Seismicity
There is a moderate-to-strong level of volcanic tremor present. Three volcanic earthquakes were recorded on Dec 26, with one measuring 2.2 beneath the crater lake. This is uncommon – and with the combination of the ongoing tremor, is reason to take note.
Significant increase in gas emissions
Changes to gas emissions are common, however recent measurements of CO2, SO2 and H2S are the largest measured in the past two decades. Again, something significant.
It was only through a combination of the increased lake temperature, volcanic tremor and gas output that GNS decided to revise the level up.
A 2km exclusion zone around the crater lake has been established.