Sep 16 2011 - August 2011 GeoNet roundup
Last month's new sites, volcano surveillance results, earthquake summaries, data products and other news from GeoNet, New Zealand's geological hazard monitoring system.
Dave Keen, GeoNet technician, installing a radio antenna above Eden Park.
Additions and upgrades to the geophysical monitoring networks
- A new borehole seismic site was completed at Eden Park (EPAZ), Auckland, at a depth of 383 m. It was installed in co-operation with the University of Auckland.
- Six new strong-motion sites were installed. They are at Kaiti Beach (GKBS) in Gisborne, Wainuiomata Hill (WANS), Waikakaho Road (BWRS) in Blenheim, Halswell School (HALS), Akaroa School (AKSS) and Methven North (MTHS). Three Canterbury sites received upgrades to more sensitive instruments: Kaiapoi North School (KPOC), Templeton School (TPLC) and Westerfield (WSFC).
- A new continuous GPS site was installed at Te Uri (TURI), near Dannevirke.
Earthquakes summary
- The most widely-felt earthquake of the month occurred on Wednesday, August 31, magnitude 4.7, 20 km south-west of Christchurch at a depth of 11 km. We have received 655 felt earthquake reports to date.
- The preliminary locations of July'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 August, except for ongoing submarine activity at Monowai Volcano.
- This month we completed gas flights at Ruapehu, Ngauruhoe and White Island, a Crater Lake sampling trip at Ruapehu and 2 days at White Island making soil gas measurements, sampling springs and fumaroles and completing a deformation survey.
Tuesday August 2 - Gas flight over White Island
Conditions were excellent, with a 10 knots wind from the south-east. SO2 flux has increased since last month but the CO2 and H2S fluxes have decreased.
| Method |
02/08/2011 |
01/07/2011 |
|---|---|---|
| SO2 emission (Cospec) | 554 | 409 |
| SO2 emission (Flyspec) | 619 | 485 |
| CO2 emission (Contouring) | 1,220 | 1,352 |
| H2S emission (Contouring) | 1.6 | 2.4 |
| SO2 emission (Contouring) | 205 | 218 |
Wednesday August 3 - Gas flight over Ruapehu and Ngauruhoe
Conditions were clear with a steady 19 knot wind. CO2 and SO2 gas levels at Ruapehu were lower than last month's survey.
No gas was detected at Ngauruhoe.
| Method |
03/08/2011 |
04/07/2011 |
|---|---|---|
| SO2 emission (Cospec) | ND* | 33 |
| SO2 emission (Flyspec) | ND | ND |
| CO2 emission (Contouring) | 234 | 1,151 |
| H2S emission (Contouring) | 0.2 | ND |
| SO2 emission (Contouring) | 6.0 | 11.6 |
| * ND - not detected | ||
Wednesday August 10 - Ruapehu Crater Lake visit
The lake was a green-grey colour and was just below overflow level. The temperature at Central vent was 18.6 °C and North vent 18.4 °C; both were sampled for gas and water. Central vent was just visible in the lake.
Thursday August 18 - White Island Spring Sample and Deformation Survey
The deformation survey shows a small, crater-wide signal of uplift (less than 10 mm). The spring flows and temperatures show a small decline from the May observations. The Crater Lake water level is up about 3m and the colour has changed to grey, with a lot of suspended matter. The temperature was 65 °C.
Tuesday August 23 - White Island Soil Gas Survey
A very steamy crater like at White Island on August 23.
Overall soil flux was down from the previous survey.
| Observations |
23/08/2011 |
20/05/2011 |
|---|---|---|
| Average | 292 | 487 |
| Sum - All Sites | 14,885 | 24,838 |
| Maximum | 7,100 | 7,174 |
| Sites Increased | n/a | 34 |
| Sites Decreased | n/a | 17 |
Three of the regular fumaroles were sampled; temperatures were similar or slightly lower than those measured in May (around 170 °C). The lake is still very steamy.
Several large landslides were heard and seen at the back of the lake throughout the day.
Thursday August 25 - Monowai Volcano
The RNZAF took photos of slicks on the surface of the sea over Monowai seamount. These show that the volcano remains active, and we have been able to see aspects of the activity on the seismograph at Rarotonga, 1,800 km away.
Reported landslides from media sources
Wednesday August 3
- A debris flow into Lake Monowai near the south side of the lake (near Tangney Bend) resulted in about a hectare of floating debris on the lake surface. GNS Science undertook a reconnaissance on August 5 and reported the landslide was a debris flow about 550 m long on a 30 degree slope, with a volume estimated at about 17,200 m3. The trigger is thought to be rapid snow melt.
Sunday August 14 – Wednesday August 17
- A predicted intense cold front brought snow to low levels to most of the country, but only minor landslides were reported as a result of this event.
Thursday August 18
- SH 3 the Manawatu Gorge was closed by a major slip at the Ashhurst end about 9 pm. On-going problems with clearance mean that the road may not re-open until mid-September.
Felt earthquakes of
July 2011
(167 located).
Shallow earthquakes of
July 2011
(1,127 located).
Deep earthquakes of
July 2011
(333 located).
