Dec 3 2005, 11:30 am - Tongariro Volcano

A magnitude 2.4 earthquake occurred on Mt. Tongariro at 2:52 am this morning. This earthquake has been followed by a series of very small earthquakes similar to, but more frequent than, activity that has been observed there over the past month. The pattern of very small earthquakes is thought to be related to increased hydrothermal activity on the mountain.

The most likely explanation for the more frequent activity after last night’s earthquake is that the earthquake shaking will have increased pressure within the hydrothermal system. This kind of triggering has often been observed at other volcanic and geothermal systems in other parts of the world. No volcanic earthquakes or volcanic tremor, which would be indicative of magma movement, has been detected.
We expect that the earthquake activity will decrease in time as pressures return to normal.

The Alert Level for Tongariro remains at Alert Level 0 — no change from typical background activity.

Terry Webb
GeoHazards Duty Officer