NEWS RELEASE, 28 FEBRUARY 2000
NEW TECHNIQUE OPENS WINDOW ON VOLCANIC AREA
New Zealand and Japanese scientists are using revolutionary
electromagnetic technology to gain a better understanding of what
drives the volcanoes and geothermal systems in the central North Island.
The subsurface processes that characterise the volcanic plateau,
caldera volcanism in particular, have been a challenge for scientists
to understand. The volcanic plateau is recognised internationally
as one of the largest and most frequently active volcanic systems
on earth.
For decades scientists have speculated about the size and location
of magma bodies (huge volumes of molten rock) that lie under what
they call the Taupo Volcanic Zone (TVZ). The TVZ is a broad belt of
volcanism and geothermal activity that extends northeast from Mt Ruapehu
to White Island. Finding a way to successfully identify and image
the magma has eluded scientists.
There are problems in using conventional seismic reflection
techniques for imaging the earth’s interior in volcanic areas.
Seismic signals, so useful for finding oil and gas in non-volcanic
areas, are difficult to interpret because of "noise" and
reverberation in the TVZ.
So scientists from the Institute of Geological &
Nuclear Sciences Limited (GNS) have turned to electromagnetic techniques
that measure the conductivity of structures within the earth’s
crust and upper mantle. One of these techniques is magnetotellurics,
which uses low frequency electromagnetic waves to measure electrical
conductivity of rocks within the earth.
By making measurements at a number of places, scientists can build
up a picture of rock formations. Geothermal fluid, clay, and magma
are good conductors of electricity and are relatively easy to identify
using this technique.
Using state-of-the-art equipment supplied by the Geological Survey
of Japan, GNS and Japanese scientists recently took magnetotelluric
measurements at a number of sites northeast of Taupo.
The data has shown several features in the crust and upper mantle.
Most intriguing is an electical conductor 10 to 12km beneath the
TVZ which scientists believe may be magma. Further measurements
will map the extent of this feature and confirm its identity.
GNS geophysicist and project leader Hugh Bibby emphasises that the
research is still in its early stages, but he believes the potential
of this technique is considerable. When magma can be identified
with confidence, it will open the door to research that has not
been possible until now.
" Identifying magma with this technique will help define new
research targets that will lead to a greatly improved understanding
of how these magmatic systems work," Dr Bibby says.
" One of the outcomes will be improved
monitoring of volcanic areas in the central North Island."
When it last erupted in 181AD, Taupo threw out 40 cubic kilometres
of volcanic material which covered parts of the central North Island
in several metres of ash and pumice. It produced a violent blast
of ground-hugging molten material that destroyed almost everything
in its path to a distance of about 90km from Taupo. It also erupted
a 50km-high ash column that affected visibility in both hemispheres.
" Prior to such big eruptions, a huge volume of magma needs
to accumulate at shallow depth. By identifying the magma we will
be able to determine if there are any changes in the rate at which
it is accumulating. Ultimately we want to find out what makes it
suddenly become unstable and produce an eruption."
Answers to these question should not only help forecast eruptions,
but will also help researchers understand the heat transfer mechanisms
occurring in the TVZ – one of the largest and youngest accumulations
of acidic volcanic rocks in the world.
Dr Bibby’s work is funded by the Foundation for Research Science
and Technology with the Japanese Government contributing additional
funds because of the relevance of the research to Japan and other
volcanic areas worldwide.
Dr Bibby has won international acclaim for his trailblazing work
in the use of electrical techniques to understand the subterranean
workings of geothermal and volcanic areas. His success at obtaining
meaningful results from large-scale field projects has seen magnetotellurics
develop into a valuable method for improving the knowledge of New
Zealand’s unique caldera volcanism.
- Caldera volcanoes usually erupt
so violently that they leave a depression in the ground.
For more information contact:
Hugh Bibby
Institute of Geological & Nuclear Sciences Ltd,
Ph: 04-570-4803 (reception), 04-570-4804 (direct)
or John Callan
Institute of Geological & Nuclear Sciences Ltd,
Ph: 04-570-1444 (w), 04-389-1245 (h),
mobile 025-402-571
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