The Shaky Isles

On 20th July, Geonet posted a Volcanic Alert Bulletin for Mount Tongariro, due to increased seismic activity.

No need for panic, just yet...

An Alert Level 1 simply means there is a "Departure from typical background surface activity" and "Signs of volcano unrest."

Mount Tongariro now has a Volcanic Alert Level of 1. This means there are now three current Level 1 volcanic alerts for volcanoes around the North Island, including Tongariro, White Island, and Ruapehu.

The Shaky Isles is an apt description of New Zealand. There are quite a few volcanoes on the North Island. As a matter of fact, there are quite a few volcanoes just around Auckland. Depending on which geologist you talk to, there are about 50 volcanoes within the Auckland Volcanic Field.

The last volcanic eruption within the Auckland Volcanic Field was about 600 years ago and formed Rangitoto out in the middle of the Hauraki Gulf.

We live on the western slope of a volcanic cone called One Tree Hill.

Nice.

Luckily, the Auckland Volcanic Field is monogenetic, meaning the next eruption will likely form a new vent, rather than erupt from an existing volcano. Of course, you never really know just where the new vent may form...

In the event a volcano does erupt, a handy plan has been prepared.

More information about volcanic hazards in Auckland can be found here.

Update 24/07/2012

Geonet has issued another Volcanic Alert Bulletin (23/07/12):

As part of our routine monitoring, we have recorded a sequence of volcanic earthquakes at Mount Tongariro since July 13, peaking in activity on July 20, with only one event today. The earthquakes cluster in a zone between Emerald Lake and the Te Māri craters at 2-7km depth. Some members of the public have also reported gas smells.

Provisional analysis of the gas samples collected at the weekend indicates the presence of volcanic gas. Our historic sampling has shown there is a mix of volcanic and hydrothermal gases and fluids at Tongariro. However the sampling on Saturday has shown a marked increase in the volcanic gas component. These results are showing the volcanic unrest indicated by the seismic data is confirmed by the gas data. We are working to complete the analysis of the gases and water samples and planning further visits later in the week when the weather improves. GNS Science volcanologists are monitoring the unrest and further information will be released as necessary.