Aug 21 2001, 10:30 am - Tongariro Volcano

Small volcanic earthquakes have been recorded beneath Mt Tongariro since at least January 2001. Since early July the number of recorded events has been steady at about 1 per day. No physical or chemical changes are apparent in steam and gas vents or hot springs in the area.

As part of our routine monitoring of seismic activity, we have detected a small change in the rate of occurrence of volcanic earthquakes at Mt Tongariro since about early July. These earthquakes are very small and are usually only 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:

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

Results available to date from water and gas sampling show no changes in the temperature or chemistry of the sampled hot springs or fumaroles. The review of seismic data, although not complete, has shown that these small volcanic earthquakes have been present since at least January 2001, while the analysis of data from a portable array has allowed us to locate the source of these events near the Te Maari craters. The rate of occurrence since early July has remained steady at about 1 event per day.

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, with another visit is planned for the beginning of September. Based on current data there is no significant reason to change the Alert Level. The Alert level for Tongariro remains at level 0.

Brad Scott
Duty Volcanologist