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| Titel |
Monitoring for volcano-hydrothermal activity using continuous gravity and local ground acceleration measurements: New deployments at Inferno Crater, Waimangu and White Island, New Zealand |
| VerfasserIn |
Arthur Jolly, Nico Fournier, Jeremy Cole-Baker, Craig Miller |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250032838
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| Zusammenfassung |
| Volcanoes with crater lakes are often characterised by shallow hydrothermal systems which
display cyclic behaviour (temperature, lake level, chemistry, etc.) and shallow seismic tremor.
Present monitoring programmes in New Zealand include routine collection of these
observables, but the associated shallow sub-surface processes are still inadequately modelled
and poorly understood. Models would be better constrained with the incorporation of
additional geophysical parameters. To this end, we have established a new test
programme to continuously monitor for micro-gravity variations at New Zealand
volcanoes. We utilise a Micro-g-LaCoste gPhone relative gravity meter having 1
Hz sample rate and a measurement precision of 1 microgal to test the viability of
gravity monitoring for volcano-hydrothermal systems. We have initially tested the
new sensor in a short term deployment (~2 months) at Inferno Crater, Waimangu,
New Zealand. Inferno shows dramatic variations in crater lake level (> 7 m range),
temperature (>40o C range) and hydrothermally derived tremor, all over a period of ~5
weeks. The amplitude and period of these observables are ideal for testing gravity
variations associated with a cycling hydrothermal system because several cycles can
be obtained in a relatively short campaign. We have deployed the gravity sensor
into a buried vault having a stable concrete base to minimise local environmental
influences. This vault is located ~20 meters from Inferno Lake edge (at high stand)
and offers sufficient noise reduction to measure the gravitational effects associated
with lake level changes. We will show results for the new gravity meter including
raw relative gravity measurements and first order corrections (earth-tide, ocean
loading, sensor level, temperature, and barometric pressure) to obtain both residual
gravity and overprinted local ground accelerations (earthquakes and local tremor).
To examine the effects of local ground vibrations on the gravity meter, we have
co-located a broadband seismometer (100 Hz sample rate). Of particular interest in this
analysis is the separation of any microgravity changes from the hydrothermal tremor
signature. Future modelling of the Inferno Crater lake will incorporate gravity, lake
level and temperature changes into a multi-phase spatio-temporal model of the
subsurface. We anticipate that separation of the gravity and seismic signals may allow
future constraint of the sub-surface hydrothermal processes which control cyclic
behaviour. We also will show results of a planned deployment of the new gravity
meter to White Island volcano, New Zealand which will occur in March 2010.
Lessons learned from the Waimangu deployment will be incorporated to understand
the long-term variations of White Islands’ hydrothermal and magmatic system. |
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