Abstract
Volcano Alert Levels (VALs) are used by volcanologists to quickly and simply inform local populations and government authorities of the level of volcanic unrest and eruption likelihood. Most VALs do not explicitly forecast volcanic activity but, in many instances they play an important role in informing decisions: defining exclusion zones and issuing evacuation alerts. We have performed an analysis on VALs (194 eruptions, 60 volcanoes) to assess how well they reflect unrest before eruption and what other variables might control them. We have also looked at VALs in cases where there was an increase in alert level but no eruption, these we term 'Unrest without eruption' (UwE). We have analyzed our results in the context of eruption and volcano type, instrumentation, eruption recurrence, and the population within 30 km. We found that, 19% of the VALs issued between 1990 and 2013 for events that ended with eruption accurately reflect the hazard before eruption. This increases to ~30% if we only consider eruptions with a VEI ≥ 3. VALs of eruptions from closed-vent volcanoes are more appropriately issued than those from open-vents. These two observations likely reflect the longer and stronger unrest signals associated with large eruptions from closed vents. More appropriate VAL issuance is also found in volcanoes with monitoring networks that are moderately-well equipped (3-4 seismometers, GPS and gas monitoring). There is also a better correlation between VALs and eruptions with higher population density. We see over time (1990 to 2013) that there was an increase in the proportion of `UwE’ alerts to other alerts, suggesting increasing willingness to use VALs well before an eruption is certain. The number of accurate VALs increases from 19% to 55% if we consider all UwE alerts to be appropriate. This higher `success’ rate for all alerts (with or without eruption) is improving over time, but still not optimal. We suggest that the low global accuracy of the issuance of VALs could be improved by having more monitoring networks equipped to a medium level, but also by using probabilistic hazard management during volcanic crisis.
Highlights
Mitigation of volcano hazards relies on the correct identification of unrest signals (Marzocchi et al 2012; Sparks et al 2012), and good monitoring networks and complete knowledge of the system
For example: are Volcano Alert Levels (VALs) issued in a timelier manner at volcanoes where there is a denser monitoring network? Are the unrest signals easier to interpret at some types of volcanoes than at others, leading to more appropriate VALs? Do more frequent eruptions at a volcano lead to more training of staff and more appropriate VALs? We investigate how the issuance of VALs varies with the volcanic system as well as with some technical and social factors
How well do VALs reflect the state of a volcano? We consider three more specific, component questions: 1) What percentage of eruptions was anticipated by appropriate alert levels? This is an eruption-centric evaluation of VALs
Summary
Mitigation of volcano hazards relies on the correct identification of unrest signals (Marzocchi et al 2012; Sparks et al 2012), and good monitoring networks and complete knowledge of the system. This allows scientists to assess the probability of an unrest episode leading to an eruption or of a return to background levels (Newhall and Hoblitt 2002; Marzocchi and Woo 2009; Lindsay et al 2010; Woo 2011; Marzocchi et al 2012; Sparks et al 2012). We discuss the role of the scientific decision-maker on the appropriate issuance of VALs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
