Aug 10 2010 - July 2010 GeoNet roundup

The completed seismic site at Waiheke Island (WIAZ), east of Auckland.

Additions and upgrades to the geophysical monitoring networks

• Two tsunami gauges were completed, one on Great Barrier Island (GBIT) and another at the entrance to Manukau (MNKT) harbour.
• A new seismic station was installed on Waiheke Island (WIAZ), extending the Auckland volcano-seismic network.

Earthquakes summary

• The most widely-felt earthquake of the month occurred on Monday, July 12, magnitude 5.3, 10 km north-west of Wairoa at a depth of 40 km. We have received 382 felt earthquake reports to date. Reports from Tuai and Wairoa included damage to items falling from shelves.
• The preliminary locations of June's earthquakes located by our analyst team are shown below.

Volcano surveillance field trips

Monday July 12 - Gas flight over Ruapehu and Ngauruhoe

This photo of Ruapehu Crater Lake has its colours adjusted to highlight the upwelling in the centre of the lake.

Conditions were excellent during the flight over the central North Island volcanoes. A good gas plume was detected with clear results for CO₂ and H₂S (carbon dioxide and hydrogen sulphide respectively).

However, the plume was quite wide and SO₂ concentrations were too low for good detection by COSPEC and Flyspec (low UV light levels at this time of year lead to higher signal to noise ratios from the spectrometers). Peaks could just be seen on the COSPEC but the data were very noisy and difficult to process. SO₂ was below the detection level of the Flyspec.

CO₂ and H₂S have increased significantly. We have not previously measured H₂S emissions higher than approximately 1 T/Day at Ruapehu. CO₂ emissions were on a part with those detected in April - June 2008 (greater than 2,000 T/Day), significantly higher than the emission rates we have measured during 2009 and the first part of 2010.

The crater lake at Ruapehu was mostly a blue-green colour, but a dark-coloured upwelling was clearly visible over the central vent. The outlet area was covered in snow, indicating that overflow was minimal, which confirms the drop in lake level recorded by the Argos logger system.

A small CO₂ plume was detected at Ngauruhoe, which gave a CO₂ emission rate of 65 T/Day. This is in line with typical emissions recorded in the past at Ngauruhoe, which can only be detected when conditions are optimum.

Thursday July 15 - Gas flight over White Island

Flying conditions were good. CO₂ and H₂S emissions were slightly higher than those measured on last month's flight, but overall are still low.

Friday July 30 - Ruapehu Crater Lake visit

After waiting for a good spell of weather, we managed to get water and gas samples from Crater Lake last Friday morning. The central vent upwelling was just visible at certain angles to the sun. We took 2 samples from the central vent to make sure we hit the right spot. The temperatures were 28.o °C and 27.4 °C. North vent was not visible and no samples were taken. The lake level was just below overflow.

Reported landslides from media sources

Monday July 5

• Minor slips were reported affecting streets in Whangarei.

Tuesday July 6

• Several slips reported to be blocking SH 2 between Napier and Wairoa in the vicinity of Lake Tutira; road was closed at 8:00 pm.
• SH 25 in the Coromandel was affected by many minor slips, but still open. Slips were reported on SH 25A between Kopu and Hikuai.
• A number of small landslides were also reported affecting roads in the eastern Bay of Plenty. SH 35 was down to one lane near Te Araroa.

Wednesday July 7

• Slips continued to affect SH 2 between Napier and Wairoa - cleared by midday. Blockages were at Devil’s Elbow and Matahorua Gorge.
• Near East Cape, SH 2 was blocked by a slip at Hospital Hill, 1 km south of Te Araroa.
• Other minor slips were reported around Gisborne.

Wednesday July 7 – Friday July 9

• A large landslide occurred at Anaura Bay, East Coast, displacing about 30,000 m3 of material. Anaura Road was blocked, isolating about 18 homes to the north, including Nuiti Beach. Road was completely impassable for vehicles, but the slip could be bypassed on foot around the beach. Contractors worked on re-establishing a roadway over the slip debris. This is a partial reactivation of a much larger, ancient landslide.

Sunday July 11 – Monday July 12

• Slips in Napier blocked access to Amner Place and two driveways in Milton Road on Napier Hill.

Saturday July 17

• A slip at Maraenui Hill closed SH 35 between Opotiki and Te Kaha for a day.

Friday July 23

• SH 3 between Mahoenui and Paemako was reduced to one lane by a slip at Monument Hill, 1.9 km north of Mahoenui.
• Heavy rain caused slips and flooding on SH 1 between Blenheim and Waipara, and SH 7 between Springs Junction and Waipara.

Felt earthquakes of
June 2010
(18 located).

Shallow earthquakes of
June 2010
(1,154 located).

Deep earthquakes of
June 2010
(430 located).