IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_4H-P2Date/Time: July 24 Poster

Quantifying the intensity of unrest: introducing the Volcanic Unrest Index (VUI)
Sally H Potter1 , Brad J Scott1 , Gill E Jolly1 , Vince E Neall2 , David M Johnston31GNS Science, 114 Karetoto Road, Wairakei, New Zealand, 2 Massey University, Private Bag 11 222,Palmerston North, New Zealand, 3 JCDR, Massey University, P.O. Box 756, Wellington, New ZealandE-mail: s.potter@gns.cri.nz

The observation and interpretation of volcanic unrest is a key element of eruption forecasting. Unrest is causedby the interaction of magma with surrounding rocks and fluids. This can result in detectable signals such as
seismicity, ground deformation and/or hydrothermal/geochemical changes. The integration and interpretation of
the multiple parameters is important for eruption forecasting and would enable the comparison of episodes, but isdifficult due to the inherent complexity of the system, multiple monitoring techniques and a variety of data formats.
No transferrable thresholds exist to divide the wide range of multivariate activity into "background" activity and"unrest", the terms commonly used in literature and Volcanic Alert Level (VAL) descriptions. To encapsulate thecomplete range of activity at a volcano during periods of quiescence (including background activity to heightenedunrest), the description Non-Eruptive Volcanic Activity (NEVA) is used.

A tool to quantify the overall intensity of NEVA is presented here, called the Volcanic Unrest Index (VUI).
Observations ranging from qualitative historical descriptions from past episodes to quantitative real-time monitoringdata can be applied to a framework. Thresholds on the framework are tailored to each volcano individually,providing a definition of "unrest". A simple calculation results in an index summarising the intensity of activity.
The creation of the VUI involved a wide literature search to ascertain the current state of knowledge of magmatic
systems and processes. Multiple iterations with volcanologists from a range of volcanic settings, institutions andcountries resulted in the tool presented here. The VUI• rates the intensity of historical unrest activity, enabling comparisons of episodes over time,• allows the rapid identification of activity reaching "unrest" status, therefore assisting with VAL changes,• prompts the early collection and analysis of historical observations to ascertain the range of NEVA intensity,
which feeds into eruption forecasting models, and• assists with the communication of multitudinous, complex information simply and rapidly to non-scientists.

A case study is presented for Taupo Caldera (New Zealand), a rhyolitic volcano which most recently erupted in 232
AD. A multi-parameter catalogue of unrest over the past 140 years at Taupo has recently been completed. The VUI
has been used to translate the complex information into an easily understood time-series plot, demonstrating thewide range of intensity of past activity at this volcano. This has helped communicate the history of NEVA at Taupo
Caldera to non-scientists from a multi-agency planning group for the mitigation of risks involved with caldera unrest(the Caldera Advisory Group). The information transfer enables the end-users to have an increased understandingof the range of past and potential future volcanic unrest episodes at Taupo.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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