Ruapehu Eruption and Quakes at Matata

Mt. Ruapehu in the central North Island erupted at 8:23 p.m. on Tuesday September 25th 2007. Within a few hours, activity associated with the earthquake swarm near Matata in the Bay of Plenty increased.

GNS Science ceased making regular reports on the status of the nation’s volcanoes available to the public at the end of June 2007, so it is not clear whether the volcano had been quiesecent since a burst of high frequency earthquakes was recorded around June 15th.

Last night’s activity appears to have been a single hydrothermal eruption of 7 minutes’ duration, and an eruption earthquake of magnitude 2.9 was recorded. Material was thrown up to 1½ kilometres from the crater, and a lahar flow was reported down the Whakapapa skifield and possibly down the Whangaehu catchment.

Roads around the mountain were closed as a precautionary measure, but re-opened before midnight. One climber was seriously injured when a volcanic missile plunged through the roof of Dome Hut and he is currently in a serious condition in an Auckland hospital.

GeoNet upgraded its website to use a Plone content management system with an in-house written front-end on the 12th of April this year, and the new website struggled to meet demand last evening. It wasn’t until after midnight that an alert bulletin on the eruption became available. Surprisingly, the time shown on the bulletin is the eruption time, instead of the time that the bulletin was released. Despite stating that more information would be posted as it came to hand, no further bulletins have been issued, apart from a small news item elsewhere on the website announcing a site visit by vulcanologists this morning.

A few hours after the eruption, at 11:56 p.m. on Tuesday 25th September 2007, a 5 km-deep magnitude 4.2 earthquake struck 10 km north-east of Matata in the Bay of Plenty (an area which has been experiencing an extended earthquake swarm since last December), placing extra stress on the Geonet website. This earthquake was followed by a magnitude 3.6 event at the same location and depth at half-past midnight on the morning of Wednesday September 26th.

Further earthquakes followed, with a magnitude 3.7 quake at 2:55 a.m., a magnitude 3.6 event at 3:45, a magnitude 3.0 quake at 5:39 and a magnitude 4.3 earthquake at 8:43 a.m. All were within 20 km of Matata, at depths of 10 km or less.

The 4th magnitude quakes have been widely reported along the Bay of Plenty coastline, as far west as Tauranga and as far inland as Kawerau.

[Compiled from data provided by the Geonet project and its sponsors EQC, GNS Science and FRST.]

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