Seismic activity

Earthquakes recorded below Tongariro

Mt Tongariro is under a watching brief after a series of small earthquakes was detected under the volcano over the past two weeks.

Stuff,

6 August, 2013

GNS Science duty volcanologist Michael Rosenberg said the quakes were not connected to the ongoing flurry of seismic activity centred in the Cook Strait and the tremors were no cause for ''undue alarm.''

Fewer than 10 quakes, all under magnitude 1.5, have been recorded on a handful of seismic monitors and are too small to be pinpointed.

''The reason we're paying attention is because of their location and we don't see quakes there very often,'' Rosenberg said.

The volcano erupted for the first time in a century at the Te Maari craters in August last year, followed by another eruption in November and scientists warn the craters could still erupt with little or no warning.

The earthquakes could just be normal volcanic background unrest but the earthquakes had piqued interest because there have been so few since 2012 and could signal changes occurring inside the volcano.

The seismic activity was not seen as a precursor to another eruption because carbon dioxide, sulphur dioxide and hydrogen sulphide gas emissions had been at low levels since the start of the year.

''If we saw these gases increase and saw more and larger earthquakes then we would think of this very likely as magma moving through Tongariro,'' Rosenberg said.

The area around the Te Maari craters is off-limits so scientists are waiting for the right prevailing winds to collect gas samples by driving or flying under volcanic plumes.

''At this stage we don't know what the activity is. There's obviously something disturbing the insides of the volcano - maybe it's just changes in the stress on the faultline.''

GNS has not changed its 0 to 5-scale Volcanic Alert Level from 1, which shows volcanic unrest or its Aviation Colour Code from green, which indicates no eruptive activity.