Focus on Taupo

People interested in activity at Taupo volcano are in for a bit of a feast at the moment. GeoNet has released an article describing their monitoring at the massive caldera volcano, and Radio New Zealand National is featuring Taupo in this week’s edition of “Earthworks”.

GeoNet released an article on monitoring activity at Taupo on Friday the 12th of December 2008. The article reminds us that the caldera volcano known as Taupo has had an impressive history of explosive and voluminous eruptions.

The gigantic Oruanui eruption, which occurred about 26,000 years ago, is the largest eruption known during the history of the area which has been active for about 300,000 years. Writing in “Awesome Forces” Bruce Houghton and David Johnston tell us that a staggering 800 cubic kilometres of pumice and ash were ejected, covering parts of the central North Island to depths of up to 200 metres. This is the equivalent of three Ruapehu-sized cones being erupted over a period of days or weeks.

Investigation of the seafloor south of the Chatham Islands has found a layer of ash from the Oruanui eruption up to 6 cm thick on the ocean floor. About 30 different eruptions from Taupo since Oruanui have been identified, including the large eruption of 181 A.D. During this event, about 45 cubic km of material was ejected, dwarfing the Mt. St. Helens eruption in the U.S.A. in 1980 and Mt. Pinatubo in the Philippines in 1991.

So Taupo, which currently hides underneath New Zealand’s largest lake, is clearly a volcano to keep an eye on.

Taupo last erupted in 181 A.D. but it is by no means extinct. There is vigorous thermal activity in the area, and the land around the lake deforms with changing pressures underneath.

During the last hundred years, there have been notable bursts of activity in and about the lake. In 1895 a swarm of earthquakes followed a series of sharp earthquakes that began with a quake estimated at magnitude 6 which struck at 6:27 on the evening of Saturday August 17th. The quake is thought to have been shallow and located to the north of Lake Taupo.

According to the Hawke’s Bay Herald of Tuesday the 20th of August 1895, Mr W. Park, postmaster at Taupo reported to the Secretary-General of the Post Office, “All the chimneys here are down except mine and two at the Lake Hotel. My battery jars are half-emptied, and in a great mess. All the residents here are camping out. The roads where cuttings exist are blocked by large slips, which have occurred all round the lake. We can see hundreds as far as the eye can reach.” Over the next few days, the postmaster continued to report strong or sharp quakes, and explosions like heavy artillery were heard. The subsequent swarm of tremors continued for about 6 weeks.

In 1922 earthquakes were felt in the Taupo area over a period of 7 months, and 2-3 metres of deformation was noted to the north of the lake. In 1964 and 1965 more than 1100 earthquakes greater than magnitude 2.7 were recorded in two months. In 1983 earthquake swarms of 10-30 events per day accompanied 50 mm of uplift over 3 months. Between 1996 and 1999 the centre of the lake rose 40 mm.

As mentioned in an earlier article on Wild Land, swarms of earthquakes have been detected beneath Lake Taupo this year. This is not unusual and smaller swarms were recorded at Taupo in 2004 and 2005.

However, the establishment of the GeoNet project has dramatically improved monitoring at Taupo and other locations. The installation of additional seismic instruments near the lake has improved the detection and location of earthquakes and detection of deformation of the land surface has been improved by the installation of continuous Global Positioning Stations.

Not only is more data being gathered, but it is being processed more quickly. The article Monitoring Activity at Taupo” includes maps of the earthquake activity at Lake Taupo between April and October this year, and reports what is suspected to be an “inflating shallow source” under the lake.

With up to 100 earthquakes per month having been recorded at Taupo between April and October, the GeoNet article notes, “…it appears that the recent activity is similar, but slightly higher than pulses of activity over the past 10 years. This style of activity may indeed be commonplace.” The enhanced monitoring by GeoNet is detecting earthquakes of lower magnitude and smaller offsets in land deformation than previously possible.

Coincidental with GeoNet’s report is one of a series of programmes on Radio New Zealand National called “Earthworks”. This Sunday’s edition, which airs after the news at 4 in the afternoon (on Sunday 14th December 2008) will focus on the Taupo volcano.

The series is somewhat quirky, showing that science can be fun as well as informative. In recent weeks presenter Howard Lukefahr has entertained us with his journey as a water droplet from high over the Southern Alps through a thousands-of-years trip through the Canterbury aquifers only to end up in the ocean after a very brief plunge through the Christchurch sewers.

The series is a mix of science and ecology, explaining such diverse topics as how the sun operates and affects our environment, the Earth’s atmosphere and weather, and the water cycle; and includes some of the scientists active in these fields of study.

This link provides access to past editions of “Earthworks”.

With GeoNet having neglected to tell us what might be inside their inflated shallow source, perhaps it is appropriate that part 5 of “Earthworks” is entitled “In the Belly of the Beast.”

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST. Other sources: Newspaper items sourced from the National Library of New Zealand “Papers Past” website. “Awesome Forces,” Te Papa Press, Wellington, 1999. ]

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