Jul 21 2011 - June 2011 GeoNet roundup

An aerial view of the Whale Island (WHRZ) seismic site. The mainland is in the background, with Mount Edgecumbe the prominent, flat-topped hill.

Additions and upgrades to the geophysical monitoring networks

• A seismic site was completed at Whale Island (WHRZ) in the Bay of Plenty near Whakatane.
• Five continuous strong-motion recorders were installed around the Hutt Valley: Petone Overbridge (PTOS), St. Bernadette's School (NBSS), Petone Victoria Street (PVCS), Upper Hutt Primary School (UHSS) and Taita Central School (TAIS).
• Following the June 13 magnitude 6.3 earthquake, two more continuous GPS units were installed above Sumner and an existing one was moved. Solar panel sizes were increased on another two sites to minimise the need to service batteries because of poor sunshine.

Earthquakes summary

• The most widely-felt earthquake of the month occurred on Monday, June 13, magnitude 6.3, 10 km east of Christchurch at a depth of 6 km. We have received 2,980 felt earthquake reports to date. It caused further building damage and liquefaction in Christchurch.
• The preliminary locations of May's earthquakes located by our analyst team are shown below.

Volcano surveillance update and field trips

Summary

• No eruptive volcanic activity occurred at any of New Zealand's active volcanoes during June.
• The temperature of the Crater Lake continued to decrease and was around 24 °C, down from a peak of 41 °C in March.
• A routine surveillance visit was made to Ruapehu's Crater Lake to sample the lake water.
• A routine gas flight was completed over Ruapehu and Ngauruhoe.
• The RV "Sonne" visited Monowai submarine volcano on June 2 and confirmed ongoing activity.
• Spring and fumarole sampling was completed at Lake Rotomahana south-east of Rotorua.
• Spring sampling was carried out on Mokoia Island in Lake Rotorua.
• A sampling trip was completed at Mokai geothermal area north-west of Taupo.

Wednesday June 1 - Gas flight over Ruapehu and Ngauruhoe

The view over Ngauruhoe's crater towards Ruapehu on June 1. The winter snows hadn't arrived!

The volcanoes were clear of cloud, and the wind speed was high (19 knots). CO₂ emission at Ruapehu was steady at 571 T/Day. Neither SO₂ nor H₂S were detected. The crater lake was blue-green in colour and no upwelling was visible.

No gas was detected at Ngauruhoe.

Tuesday June 21 - Ruapehu Crater Lake visit

Gas and water samples were taken at the Central and North Vent. The temperature was 24.1 °C. The lake had a uniform turquoise colour with no obvious upwellings. The water was overflowing at the outlet.

Reported landslides from media sources

Wednesday June 8

• SH 2, the Rimutaka Hill, was affected by a slip blocking one lane near the summit after overnight rain.

Monday June 13

• A large number of landslides in the Port Hills area of Canterbury were re-activated by a magnitude 6.3 aftershock centred at Taylors Mistake. A number of new landslides were triggered, damaging many houses in Mount Pleasant, Redcliffs, Sumner and Scarbrough. There were no casualties from the landslides as the susceptible properties remained vacant after the February 22 Christchurch earthquake. Of particular note were a large reactivation of the rock-falls at Peacock’s Gallop (a former quarry), taking the cliff top back 15 m, taking half a house with it, and at Scarborough where the crack behind the cliff top from February became the new top of the cliff. The historic lighthouse at Godley Head has been undermined by a rock-fall beneath its foundations and the access steps leading to it from the cliff edge above have been lost due to a rock-fall. Being further from the epicentre of the latest shock, there was less new landslide damage at Lyttelton than in February.

Saturday June 18

• Stafford Drive in Mapua near Nelson was closed due to landslips, and one lane of the Takaka Hill road was blocked by slips near the summit.
• A slip came down on West End Road, Ohope Beach, just before midday, killing the occupant of a house. Heavy rain and falling pohutukawa trees on the cliff edge are implicated in these failures, of which there have been many previously in this area. In the same rainstorm event another house along West End Road was also damaged by a slip and others threatened.

Saturday June 25

• State Highway 2 near Matata was totally blocked due to a large land slip approximately 2 kilometres north of Matata town centre; it was expected to take 3 to 4 hours to clear.

Felt earthquakes of
May 2011
(158 located).

Shallow earthquakes of
May 2011
(1,641 located).

Deep earthquakes of
May 2011
(441 located).