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Seismic signature of Tongariro eruption. GeoNet

Last night Mount Tongariro burst into life, erupting for the first time in over 100 years. The eruption raised the Geonet volcanic alert from level 1 to 2, with an accompanying aviation colour code of red. The Tongariro alert level had been upped to level 1 on 20th of July 2012, due to increased seismic activity and other signs of volcanic unrest.  However, according to GNS volcanologist Michael Rosenberg, last night’s eruption was still a surprise, as seismic activity under the volcano appeared to be on the decline in recent days.  He warned that although the volcano seems relatively quiet at the moment, this early in the eruptive sequence it is impossible to know whether Tongariro’s activity will escalate in to a full-scale eruption.

According to GNS science, Tongariro is a large volcanic complex consisting of many cones that have been constructed over the past 275,000 years. There have been five recorded prior eruptions from the Te Mari craters, the last one in 1897.  Some 12 homes on the southern shores of Lake Rotoaira (~6 km away from the eruption) had a spectacular view of last night’s event, and eyewitness accounts confirm that the current eruption began around 11:50 pm yesterday with a violent explosion, accompanied by a red glow and flashes of lightning. Rocks and sand-like ash were apparently ejected from the volcano, causing concern for some residents, who reported seeing new vents on the side of the mountain (stuff.co.nz). The prevailing westerly winds have so far been driving the ash cloud to the east and south, with ash falls reported as far away as Napier. There aren’t any evacuation orders at present, but GNS and Civil Defence continue to monitor the situation closely.

Ash fall near Tongariro. Peter Drury photo.

A level 2 alert indicates the onset of “minor eruptive activity”, while the red aviation code means that significant ash is being ejected into the atmosphere. An ash plume extended up to 7 km high following the eruption, with up to 5 cm of ash settling near Mt. Tongariro. Both State Highway 46 and the Desert Road have been closed due to poor visibility. Volcanic ash dispersion is especially disruptive to air traffic; in addition to the dangers of lightning and reduced visibility within ash clouds, abrasive ash particles can damage aircraft engines, instruments and windscreens. Ingestion of ash into jet turbine engines can result in melting of the particles, which can then re-solidify and accumulate on the turbines, potentially causing engine stall.

So far, relatively minor air traffic delays are being reported by Auckland International Airport, with most international flights operating as scheduled. However, there are some delays and cancellations to domestic flights, particularly those from the eastern-southeastern North Island, where the ash cloud is having the most impact (e.g. Napier, Gisborne, Palmerston North). Civil Defence is cautioning people affected by the ash cloud to remain indoors and close all windows and doors.

No ash has yet been reported on the Whakapapa or Turoa ski fields, which are open for business as usual today.

A time lapse sequence of images from GNS’s Tongariro volcano camera is available at geonet.org.nz; the images do not appear to capture the actual eruption, likely because cloud cover had obscured the mountain.

Stay tuned for further developments.

Mount Tongariro prior to the eruption. GNS.