Sensitivity to volcanic field boundary

Abstract

Volcanic hazard analyses are desirable where there is potential for future volcanic activity to affect a proximal population. This is frequently the case for volcanic fields (regions of distributed volcanism) where low eruption rates, fertile soil, and attractive landscapes draw populations to live close by. Forecasting future activity in volcanic fields almost invariably uses spatial or spatio-temporal point processes with model selection and development based on exploratory analyses of previous eruption data. For identifiability reasons, spatio-temporal processes, and practically also spatial processes, the definition of a spatial region is required to which volcanism is confined. However, due to the complex and predominantly unknown sub-surface processes driving volcanic eruptions, definition of a region based solely on geological information is currently impossible. Thus, the current approach is to fit a shape to the known previous eruption sites. The class of boundary shape is an unavoidable subjective decision taken by the forecaster that is often overlooked during subsequent analysis of results. This study shows the substantial effect that this choice may have on even the simplest exploratory methods for hazard forecasting, illustrated using four commonly used exploratory statistical methods and two very different regions: the Auckland Volcanic Field, New Zealand, and Harrat Rahat, Kingdom of Saudi Arabia. For Harrat Rahat, sensitivity of results to boundary definition is substantial. For the Auckland Volcanic Field, the range of options resulted in similar shapes, nevertheless, some of the statistical tests still showed substantial variation in results. This work highlights the fact that when carrying out any hazard analysis on volcanic fields, it is vital to specify how the volcanic field boundary has been defined, assess the sensitivity of boundary choice, and to carry these assumptions and related uncertainties through to estimates of future activity and hazard analyses.

Fire From Volcanic Activity: Quantifying the threat from an understudied hazard

“…The field covers an area of 360 km 2 and has produced at least 53 separate vents over the course of its eruptive history, representing explosive (magmatic and phreatomagmatic) and effusive eruption styles (Hopkins et al, 2021). New activity is expected in the future, likely to take place from a new vent either on land or in the underwater areas that lie within the field (Runge et al 2015;Hopkins et al 2021). No spatiotemporal pattern has been detected among the 53 prior eruptive centres, rendering the location of a future eruption uncertain (Bebbington and Cronin, 2011;Hopkins et al 2021).…”

A New Inclusive Volcanic Risk Ranking, Part 1: Methodology

“…A few centimeters of tephra can already have an impact on transportation, electric power, and water supply, whilst 10 cm of tephra, particularly if wet, could trigger structural damage to buildings (Ewert et al, 2005). In the case of monogenetic volcanic fields (MVF), the analysis was carried out considering all the exposed elements within the MVF as well as considering buffer distance of 5, 10 and 30 km from the rim of the field, due the variation in the spatio-temporal behavior of volcanic fields (Runge et al, 2014;Runge et al, 2015).…”

“…The presence of any number of residential buildings, transportation, power, water, and telecommunication infrastructures, as well as critical facilities and economic activities (agriculture, livestock, forestry, fishing, mining, industry, tourism) was scored with values of 1, 2, 3 and 4 considering the first appearance in 100, 30, 10 and 5 km from a central volcano, respectively or in case of MVF from a buffer (as Runge et al (2014) and Runge et al (2015) suggest) of 30, 10, and 5 km or first appearance within field (Table 2).…”

Thermal impacts of basaltic lava flows to buried infrastructure: workflow to determine the hazard

“…This could result in the formation of a Fig. 2 Map of the Auckland Volcanic Field including all known eruptive vents and volcaniclastic deposits (after Kermode 1992), the volcanic field boundary (Runge et al 2015), and the location of the vent in the Birkenhead DEVORA scenario (Hayes et al 2018). Inset shows location of Auckland on the North Island of New Zealand lava delta (e.g., Skilling 2016) and/or explosions caused by lava-water interactions (e.g., Mattox and Mangan 1997;Hamilton et al 2010;Noguchi et al 2016).…”