Volcanoes - Ministry of Civil Defence and Emergency Management

comprehensive diagnostic set of information for
predicting changes in volcanic activity, and assessing
volcanic hazard.
EVENT RESPONSE
Preparing to collect water samples from Mt. Ruapehu's Crater Lake.
Photo: GNS.
a gradual increase in the magnesium to chloride
(Mg/Cl) ratio in lake waters which suggests that there
was interaction between lake waters and fresh magma
during this period.
THERMAL AND MAGNETIC MONITORING
Any eruption is likely to be preceded by increases
in the underground temperature, but heat moves slowly,
so eruptions often occur before any surface temperature
changes are observed. Fumarole temperatures, or
analysis of the heating of crater lakes, can give an
indication of the temperature at depth. Another
technique is to use the fact that volcanic rocks become
demagnetised at temperatures of about 500 ºC. This
means that increases in the underground temperature
are likely to produce decreases in the total magnetic field
at the surface. White Island volcano has been found to
produce large magnetic changes as a result of changing
underground temperatures.
All of the above techniques, coupled with
changes in deformation and seismicity provide a
The natural response of a volcanologist to an
eruption (or a seismologist to an earthquake) is to head
towards its source. This used to be the only possible
response, as the monitoring instruments we had were
not connected to data centres and data had to be
retrieved on site. In 1993 the seismometers monitoring
the Tongariro National Park volcanoes and the Rotorua/
Taupo area were connected by leased telephone lines
to the GNS Wairakei Research Centre near Taupo, so
they could be recorded there. However they were only
properly monitored if someone watched the recording
drums, so during volcanic crises it was necessary to have
staff in the office 24 hours/day for this purpose.
The new GeoNet response system is based on
duplicated data centres, at the GNS Gracefield (Lower
Hutt) and Wairakei sites, with data paths arranged so
that all data is available at either centre, even if the
other centre is out of action. By then putting processed
data on web servers, it can be accessed by staff from any
Internet connection. Two Geohazards Duty Officers
are on duty at any time, one in the Wellington area
and one in the Central North Island. They are alerted
by pager when seismicity levels increase at any of the
active volcanoes, as well as by significant earthquakes
anywhere in New Zealand. With Broadband internet
connections to the Duty Officers' homes, and laptops
equipped with high speed data modems, they can readily
check the condition of the volcanoes and the monitoring
equipment at any time, and provide responding agencies
with information to assist decision-making.
Another aid to the Duty Officers are the volcano
cameras which have been installed since 2000. Their
pictures have become one of the most visited parts
of the GeoNet website at http://www.geonet.org/
volcanocam.htm. They normally take photos every 30
minutes at five sites, giving general views of Ruapehu,
Ngauruhoe, White Island and Mt. Taranaki volcanoes,
together with a view within the White Island crater.
This last view requires a short radio link to a ridge above
the crater, and then an 80 km radio link, to provide
communication between the camera and a computer in
the Whakatane office of Environment Bay of Plenty. In
times of high volcanic activity, the time between pictures
can be reduced to a few minutes. If bandwidth is
available, we are hoping to move towards some kind of
video system to supplement or replace these cameras.
GNS allocates an Alert Level to each of the
recently active volcanoes, depending on their level
of activity. In normal situations, changes in the Alert
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TEPHRA
June 2004