Communicating the status of volcanic activity in New Zealand, with specific application to caldera unrest

Abstract

Volcanic eruptions can negatively impact social, economic, built, and natural environments. Volcano Early Warning Systems (VEWSs) assist with mitigating the risk of eruptions. Volcanic Alert Level (VAL) systems are a component of VEWSs and are commonly used to communicate the status of volcanic activity. Volcanic unrest, which may consist of seismicity, deformation, degassing, and geothermal changes, is a status often used in communicating warnings as it is the key indicator of an impending eruption. However, it can be difficult to distinguish between ‘background’ activity and ‘unrest’. This research focuses on recognising changes at a caldera volcano when it begins to show signs of unrest, and the communication of this information using the VAL system.

New Zealand’s VEWS is summarised and the VAL system is explored. Influences on the determination of the VAL and potential foundations of VAL systems are identified. For the first time globally a qualitative ethnographic methodology is used to develop a new VAL system, involving interviews, observations over three years, and document analysis. To assist with distinguishing ‘unrest’ from ‘background’ activity at volcanoes, a new, innovative tool called the Volcanic Unrest Index (VUI) was developed. The VUI is a semi-quantitative tool that defines unrest and integrates multi-parameter qualitative and quantitative data, enabling a world-first comparison of the intensity of unrest. It provides a simple way to communicate the status of a volcano with non-scientists. A catalogue of historical caldera unrest was developed for Taupo Volcanic Centre (TVC), New Zealand. Through estimating the VUI, 16 episodes of unrest between 1872 and 2011 were identified, with a recurrence rate of one episode every nine years, and a median duration of slightly less than five months. Socio-economic impacts have resulted from many of these unrest episodes.

These findings suggest the VAL could have been raised during past unrest at TVC, including in 2008-10. However, influences on the decision to change the VAL, including potential socioeconomic impacts, may cause a delay in raising the VAL during future unrest. These findings contribute towards more effective communication of the status of volcanoes in New Zealand in the future, particularly at calderas.