Apr 8 2011 - March 2011 GeoNet roundup

Looking down the radio aerial at the Kaimai (KMRZ) seismograph station.

Additions and upgrades to the geophysical monitoring networks

• A new strong-motion site was installed at the Eyrewell Observatory (EYRS). This is the site of the national geomagnetic observatory.
• One Etna at Hanmer Springs Emergency Centre (HSES) and three CUSP-3 strong-motion instruments at Waikari (WAKC), Dunsandel School (DSLC) and Mayfield School (MAYC) were upgraded. All of these new instruments are Kinemetrics Basalts which are configured to provide continuous streaming at 20 samples per second, as well as recording events at 200 samples per second.
• Three new Regional Seismic Network sites were completed, one at Kaimai (KMRZ), one near Murupara (MUGZ) and one near Ohakea (OHWZ).

Earthquakes summary

• The most widely-felt earthquake of the month occurred on Friday, March 4, magnitude 4.7, 10 km north-east of Upper Hutt at a depth of 30 km. We have received 3,646 felt earthquake reports to date - 3 of these were for slight damage to household contents.
• The preliminary locations of February's earthquakes located by our analyst team are shown below. Due to the high numbers of aftershocks of the Christchurch earthquake of February 22, not all events for this month have been fully analysed yet.

Volcano surveillance update and field trips

Summary

• Volcanic activity throughout New Zealand was low during March.
• The heating cycle has continued at Ruapehu with the Crater Lake temperature reaching 41 °C on March 1. Associated with the current heating cycle there have been small changes in lake chemistry and minor seismic activity. These observations are consistent with the volcano-hydrothermal system now being more active and heating the Crater Lake water.
• White Island also remains quiescent with minor declines in fumarole temperatures and a continued drop of water level in the Crater Lake.
• Routine gas flights were completed at White Island, Ngauruhoe and Ruapehu.

Thursday March 24 - Gas flight over Ruapehu and Ngauruhoe

Aerial view of the Crater Lake during a gas sampling flight on March 24.

Conditions were excellent. The volcanoes were clear of cloud, and the wind was steady at around 14 knots.

CO₂ emissions at Ruapehu were high at 2,074 T/Day when compared with the moderate CO₂ emissions (> 400 T/Day) detected in February, but cloud on that occasion prevented a full measurement. SO₂ emissions were very low, and were barely detectable by COSPEC. H₂S emissions were moderate.

The crater lake was blue-green in colour, and a weak upwelling was visible as a darker colour in the middle of the lake.

Ngauruhoe was also visited. Faint traces of CO₂ and H₂S were detected. These were consistent with typical emissions seen at that volcano.

Monday March 28 - Gas flight over White Island

Conditions were windy, with a 25 knot wind from the south-east, so conditions in the lee of the volcano were pretty rough.

CO₂ and H₂S were up on last month with SO₂ (Cospec) decreasing.

There appeared to be a lot of discoloured water around the volcano, probably due to erosion from heavy rainfall occurring over the previous weekend.

Reported landslides from media sources

No landslides were reported during March 2011.

Felt earthquakes of
February 2011
(280 located).

Shallow earthquakes of
February 2011
(1,652 located to date).

Deep earthquakes of
February 2011
(358 located to date).