Jun 24 2011 - May 2011 GeoNet roundup

Technicians putting the finishing touches to the Ruatahuna (RTZ) National Seismograph Network site.

Additions and upgrades to the geophysical monitoring networks

• A new National Network site was established near Ruatahuna (RTZ). This is a solar powered site with satellite communications.
• A new combined seismic (RUGZ) and continuous GPS (RAUM) site was completed in the Raukumara Range, about 35 km east of Opotiki.
• Two continuously recording strong-motion accelerographs were installed, one at Makara Bunker (MKBS) and another at Lower Hutt IRL (LIRS).

Earthquakes summary

• The most widely-felt earthquake of the month occurred on Tuesday, May 10, magnitude 5.3, 20 km west of Christchurch at a depth of 15 km. We have received 2,017 felt earthquake reports to date.
• The preliminary locations of April'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 May.
• The temperature of the Crater Lake continued to decrease and was around 30 °C, down from a peak of 41 °C in March. Other available monitored indicators also suggested a slow decrease of activity at that time, hence the volcano was no longer considered in a state of elevated unrest. The Aviation Colour Code was returned to Green; the Volcanic Alert Level remains at Level 1.
• A routine surveillance visit was made to Ruapehu's Crater Lake on May 10 to sample the lake water.
• Routine surveillance trips were made to White Island on May 20 and May 24 to conduct fumarole and spring sampling, and to make deformation, soil gas and magnetic surveys.
• A routine gas flight was completed at White Island.

Tuesday May 10 - Ruapehu Crater Lake visit

The lake was its normal uniform turquoise colour with no obvious upwellings, although the water surface was disturbed due to a moderately strong northerly wind. The highest temperature recorded at the central vent was 25.5 °C and the lake was overflowing at the outlet.

Tuesday May 10 - Tongariro lake and fumarole sampling

The May 10 view of Upper Tama lake with Ngauruhoe in the background.

The annual Tongariro and Ngauruhoe was conducted on May 10. In this yearly survey, we visit and sample several hydrothermal features in the Tongariro massif.

The Ngauruhoe temperatures and fumarole pressures were slightly lower than last year's survey results, and the main fumarole was sampled for gases and isotopes. A fumarole was sampled at Red Crater and another on the Oturere face below the Lower Emerald lake. Pressures and temperatures were lower at the Red Crater, but an altered area on the Oturere face appeared larger that the previous year with a large steam discharge. The fumarole sampled was at same temperature but with a slightly higher pressure.

Te Māri and Central craters were visited but not sampled. Temperatures at Central Crater were down compared to last year and the fumaroles are now very weak. The Te Māri temperatures were similar to last year. The springs and lakes were sampled and no changes were seen compared to last year.

Thursday May 19 - Gas flight over White Island

Conditions were excellent, with a 13 knot wind from the south-west. CO₂ emission was lower but SO₂ and H₂S emissions were similar to those measured in March.

Friday May 20 - White Island Soil Gas and Deformation Surveys

During the visit deformation and soil gas measurements were made. No significant deformation was measured. The mean flux was similar to the last survey three months ago.

Tuesday May 24 - Spring and fumarole sampling at White Island

Fumaroles and springs were sampled and flows measured. The fumarole and spring temperatures were similar to those measured on the March 2011 visit. The Crater Lake temperature has risen to 71.5 °C. This is the hottest it has been since February 2007 when it reached 74.2 °C. The crater is very obviously steamy and it is hard to see the surface of the lake.

A magnetic survey was also completed, occupying 52 different sites.

Reported landslides from media sources

Monday May 2

• Heavy rain continued to cause problems in Hawke’s Bay with several houses threatened by large landslides. About 60 houses were affected by slips and flooding and a state of emergency was declared. The worst affected areas included coastal settlements of Kairakau, Pourerere, Aramoana and Mangakuri beaches. At Kairakau two houses were red-stickered, as authorities were concerned about the stability of the cliff face behind the houses. There had also been one slip in Pourerere.
• Elsewhere in the North Island, Tarewa Road, Paparatu Road and Waingake (between Wairoa and Gisborne) were affected by slips as a result of the same band of heavy rain that affected Hawke’s Bay. In the Coromandel, SH 27 (the Thames coast road), was briefly blocked by a large slip at Ruamahanga, 15 km north of Thames, at about 10pm.

Tuesday May 3

• Continued heavy rain in Hawke’s Bay caused fears that an unstable hillside at Pourerere Beach, 30 km east of Waiapawa, might endanger houses and caravan parks. 29 house and 31 caravan parks were deemed to be at risk.
• A minor slip was reported on SH 25a, the Kopu-Hikuai road in the Coromandel.

Monday May 9

• There were delays on SH 38 40 km north of Wairoa as a slip was being cleared.

Tuesday May 10

• Keelan Road off SH 35 at Takapau on the East Coast north of Te Puia Springs was closed by a landslide.

Thursday May 12

• Whakarau Road between Te Karaka and Moutohora (near Matawai) was closed to heavy vehicles and almost impassable because of slips.

Friday May 13

• Ihungia Road near Takapau on the East Coast was affected by landslips.
• Tapuaeroa Road at Takamore (west of Ruatoria) was affected by a slip at McClutchie’s Bridge.
• Waiomatatini Road at Wairoa (near Ruatoria) was affected by landslips at Kainanga Hill.

Sunday May 15

• Minor slips as a result of heavy rain in the Wellington area in the early morning partially blocked SH 2 north of Melling and a slip delayed trains on the Johnsonville line.

Monday May 16

• Waipiro Road between Te Puia Springs and Waipiro Bay was affected by slips 2 km north of Te Puia Springs.

Friday May 20

• Paparatu Road, about 10 km south-west of Waingake (in the Gisborne area), was still affected by landslips from May 2 and was passable with care.

Monday May 23

• Herepuru Road 3 km west of Matata, Bay of Plenty, was closed by landslips between the locked gates and SH 2.

Thursday May 26

• Heavy rain sweeping across the North Island caused slips in the Coromandel, closing the Port Charles Road at Sandy Bay
• In the Nelson area, Bridge Valley Road, Wakefield, had one lane affected by slips.
• The Kaiteriteri-Sandy Bay Road was affected by slips and a fallen tree.
• Slips also caused road closures on the Takaka Hill, Maitai Valley Road and SH 6 at Canvastown.

Felt earthquakes of
April 2011
(209 located).

Shallow earthquakes of
April 2011
(1,700 located).

Deep earthquakes of
April 2011
(402 located).