Wednesday, July 25, 2012

Famed Mount Tongariro in New Zealand Shows Spike In Seismicity

The volcano made famous in New Zealand (for something other than erupting) by the movie franchise "The Lord of the Rings", as a stand in for "Mount Doom" is showing signs of increased seimicity and gas levels. The Smithsonian GVP's report today had this to say about Tongariro:

"TONGARIRO North Island (New Zealand) 39.13°S, 175.642°E; summit elev. 1978 m

A sequence of small volcanic earthquakes beneath Tongariro was detected by a few of the seismometers in the permanent network. Earthquakes with magnitudes less than 2.5 were clustered between Emerald Crater (E of the summit) and the Te Mari craters (2 km E east of Ketetahi hot springs on the N flank) at 2-7 km depth. The sequence started on 13 July, soon declined, and then again increased during 18-20 July. The Alert Level was raised to 1 (on a scale of 0-5) and the Aviation Colour Code was raised to Yellow (on a four-color scale) on 20 July.In response to the increased seismicity, GeoNet installed four portable seismographs and conducted gas and spring sampling. During 21-22 July seismicity declined; one event was detected on 23 July.

Provisional analysis of the gas samples collected during 21-22 July indicated a marked increase in the volcanic gas component of the typical mix of volcanic and hydrothermal gases. Residents reported a gas odor.Geologic Summary.

Tongariro is a large andesitic volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu volcano) to Te Mari crater (including vents at the present-day location of Ngauruhoe) were active during a several hundred year long period around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. The youngest cone of the complex, Ngauruhoe, has grown to become the highest peak of the massif since its birth about 2500 years ago. The symmetrical, steep-sided Ngauruhoe, along with its neighbor Ruapehu to the south, have been New Zealand's most active volcanoes during historical time."

Tongariro's last known eruptive period was from 1974-1977 according to the Smithsonian GVP. The eruptions have been mostly pyroclastic in nature, with a history of phreatic eruptions and cone building events. The volcano has remained relatively quiet since 1977, and contains a crater lake at the NE summit, as well as a few smaller ones called 'The Emerald Lakes'. Plenty of fumerolic activity occurs near the lakes, which were apparently a nice place until recently to take a dip.

An eruption at Tongariro today has the potential to disrupt air travel for New Zealand and Australia, and older lava flows (not historical) cover farmlands to the NE of the summit. 

1 comment:

  1. Very informative post! Thanks for bringing latest updates about Tongariro and the volcanic eruption underneath of the summit. I hope major eruption will not cause again after 1974-1977. This type of eruption proves very deadly for us and wild animals. Thanks.
    famous volcanoes

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