Improving volcanic ash fragility functions through laboratory studies: example of surface transportation networks

Abstract

Surface transportation networks are critical infrastructure that are frequently affected by volcanic ash fall. Disruption to surface transportation from volcanic ash is often complex with the severity of impacts influenced by a vast array of parameters including, among others, ash properties such as particle size and deposit thickness, meteorological conditions, pavement characteristics, and mitigation actions. Fragility functions are used in volcanic risk assessments to express the conditional probability that an impact or loss state will be reached or exceeded for a given hazard intensity. Most existing fragility functions for volcanic ash adopt ash thickness as the sole hazard intensity metric that determines thresholds for functional loss. However, the selection of appropriate hazard intensity metrics has been highlighted as a crucial factor for fragility function development and recent empirical evidence suggests that ash thickness is not always the most appropriate metric. We review thresholds of functional loss for existing published surface transportation (i.e. road rail, maritime and airport) fragility functions that use ash thickness. We then refine these existing functions through the application of results from a series of recent laboratory experiments, which investigate the impacts of volcanic ash on surface transportation. We also establish new fragility thresholds and functions, which applies ash-settling rate as a hazard intensity metric. The relative importance of alternative hazard intensity metrics to surface transportation disruption is assessed with a suggested approach to account for these in existing fragility functions. Our work demonstrates the importance of considering ash-settling rate, in addition to ash thickness, as critical hazard intensity metrics for surface transportation, but highlights that other metrics, especially particle size, are also important for transportation. Empirical datasets, obtained from both post-eruption field studies and additional laboratory experimentation, will provide future opportunities to refine fragility functions. Our findings also justify the need for rapid and active monitoring and modelling of various ash characteristics (i.e. not ash thickness alone) during volcanic eruptions, particularly as potential disruption to surface transportation can occur with only~0.1 mm of ash accumulation.

Agriculture and forestry impact assessment for tephra fall hazard

“…However, with the data currently available, it is not possible to robustly account for these factors in the proposed functions. This is noted in the development of tephra fall fragility functions for infrastructure and the built environment, where tephra thickness or load (kg m −3 ) are the selected HIMs [Wardman et al 2010;Jenkins et al 2014b;Blake et al 2017].…”

“…This is a limitation of both the development of fragility functions, but also a known constraint of temporal hazard layers across the eruption sequence, and as a result the subsequent risk assessments [e.g. Blake et al 2017;Wilson et al 2017;Juniper 2018;Wild et al 2019]. These temporal factors may dramatically decrease the maximum damage/production loss received by farmers after an event, as some of the initial impact could be mitigated (e.g.…”

Integrating criticality concepts into road network disruption assessments for volcanic eruptions

“…The impact severity defines the level of service loss for a road segment. This is important because volcanic eruptions can affect road networks in different ways with different levels of severity (Wilson et al 2014;Blake et al 2017c). For example, some segments may only require speed restrictions, whilst others may require complete closure (Blake et al 2017c).…”

“…This is important because volcanic eruptions can affect road networks in different ways with different levels of severity (Wilson et al 2014;Blake et al 2017c). For example, some segments may only require speed restrictions, whilst others may require complete closure (Blake et al 2017c). Finally, the length of road affected was used to provide an indication of the spatial extent of disruption and the level of resources and/or time required to restore functionality.…”

“…Cracks and fissures in roads can also occur due to thermal effects from the flows or from ground deformation associated with volcanism (Blong 1984;Wilson et al 2014), whilst ballistic impacts can cause irregular depressions in the road surface (Blong 1984;Wilson et al 2014;Blake et al 2015). The impacts from tephra fall on roads are not typically destructive, but are disruptive and widespread, even at relatively modest thicknesses of a few millimetres (Blong 1984;Wilson et al 2012;Blake et al 2017c). Visibility can be severely reduced during tephra fall or as a consequence of remobilisation of tephra (Blake et al 2018).…”