Earthquake activity continued at a steady rate. White Island and Mt. Ruapehu remained at Alert Level 1. A slow-slip event was detected near Gisborne.
GeoNet, the U.S. Geological Survey and GNS Science reported on 28 earthquakes in the New Zealand area between the Kermadec Islands in the north, and the Auckland Islands to the south during March 2010.
The magnitude distributions were as follows:
M6 to 6.9 (none), M5 to 5.9 (9), M4 to 4.9 (10) M3 to 3.9 (7).
An additional 2 events in the magnitude two range were deemed worthy of mention.
Earthquake activity in the Kermadec Islands was concentrated in the southern part of the island chain during March. Two quakes of magnitude 5.0 and 4.9 struck to the north of Raoul Island on the 19th and 22nd. Four events with magnitudes between 4.9 and 5.4 were detected within 300 km of L’Esperance Rock in the southern Kermadecs, but none were felt ashore in New Zealand.
On the 31st a magnitude 5.2 quake struck 30 km north of White Island at 8 a.m. The 130 km-deep quake was felt from Whangamata to Gisborne.
A slow-slip event commenced near Bartletts, south of Gisborne, mid-way between two slow-slip zones that had been active during January and February. Activity began about the 15th of March and, by the end of the month, the interface between the Pacific and Australian tectonic plates had quietly slipped by about 70 mm.
A burst of earthquake activity west of Te Anau ranged between 40 km north-west and 80 km west of the town between the 14th and 20th. The first and largest quake, a magnitude 5.0 event, was also the shallowest at 7 km and was felt in Fiordland and Southland. A magnitude 4.0 quake on the afternoon of the 16th was not felt, but a magnitude 4.3 quake at 9:22 p.m. on the 20th (the deepest of the series) was felt widely in the southern part of the South Island.
A cluster of shallow earthquakes near the Snares Islands in the Southern Ocean comprised three quakes over less than twenty minutes on the evening of the 18th. A magnitude 4.9 quake struck at 7:24 p.m. followed by a magnitude 5.7 event at 7:28 and a magnitude 5.1 earthquake fourteen minutes later. The quakes were centred 230-250 km north of the Auckland Islands, about 150 km south-west of the Snares. The largest of the three was felt ashore in southern parts of Southland and Otago and at Queenstown.
The following morning a shallow magnitude 5.5 earthquake struck north of the cluster, closer to New Zealand. This quake was centred 260 km west of Invercargill (230 km north-west of The Snares) at a depth of 33 km. This event was not widely felt, with felt reports being filed from Queenstown and Invercargill.
Regular reporting of the status of New Zealand’s volcanoes ceased at the end of June 2007, with the closure of the Hazard Watch service. GNS Science now only issues bulletins which record significant changes in volcanic behaviour.
No Alert Bulletins were issued by GNS Science during March 2010.
Springs and fumaroles were sampled at White Island on the 2nd of March, and flows hadn’t changed much since the November 2009 sampling trip. Crater lake temperatures were similar to those recorded in November, with Cindy’s Mistake Pool up by five degrees. Water levels were similar to November measurements.
A sampling trip to Ruapehu’s crater lake found the lake temperature was 23.8 °C.
At the end of March 2010, New Zealand’s active volcano status can be summarised as follows:
Raoul Island (Alert Level 0).
White Island (Alert Level 1).
Mt Ngauruhoe (Alert Level 0).
Mt Ruapehu (Alert Level 1).
[Compiled from data supplied by GNS Science, US Geological Survey, GeoNet, and their contributing agencies.]