Jul 20 2001, 9:00 am - Tongariro Volcano

Small volcanic earthquakes have been recorded beneath Mt Tongariro since February 2001. These by themselves do not give reason to change the Alert Level.

As part of our routine monitoring of seismic activity, we have recorded several volcanic earthquakes per month at Mt Tongariro since at least February. These earthquakes are very small and have only been well recorded by one seismometer in our permanent network. Without data from at least three seismometers it is not possible to locate the exact source of these volcanic earthquakes.

To better understand the significance of these earthquakes we have:

• deployed portable seismic recorders on Mt Tongariro
• reviewed other available seismic data
• conducted sampling of selected hot springs, crater lakes and fumaroles in the area

The review of seismic data has shown that these small volcanic earthquakes have been present since at least February 2001, while the analysis of data from a portable array operated by Cambridge University (January-May) has allowed us to locate one of these events near the Te Maari craters. Results available to date from water and gas sampling show no changes in the chemistry of the springs or fumaroles.

Mt Tongariro is a volcano complex that lies to the north of Ngauruhoe. It consists of numerous craters and vents. Te Maari craters lie about two kilometres east of Ketetahi hot springs on the north side of Mt Tongariro. The Te Maari craters are the last craters to be active on Tongariro. Small ash eruptions were recorded from these craters in 1869 (accompanied by a violent earthquake), June 1886, November 1892 and November-December 1896.

At this time we have no reason to believe that an eruption will occur at Te Maari in the near future. However we will continue to monitor the situation. Based on the data available to date there are no reasons significant enough to change the Alert Level. The Alert level for Tongariro remains at level 0.

Brad Scott
Duty Volcanologist