Abstract

Lahars are rapid flows composed of water and volcaniclastic sediments, which have the potential to impact residential buildings and critical infrastructure as well as to disrupt critical services, especially in the absence of hazard-based land-use planning. Their destructive power is mostly associated with their velocity (related to internal flow properties and topographic interactions) and to their ability to bury buildings and structures (due to deposit thickness). The distance reached by lahars depends on their volume, on sediments/water ratio, as well as on the geometrical properties of the topography where they propagate. Here we present the assessment of risk associated with lahar using Vulcano island (Italy) as a case study. First, we estimated an initial lahar source volume considering the remobilisation by intense rain events of the tephra fallout on the slopes of the La Fossa cone (the active system on the island), where the tephra fallout is associated with the most likely scenario (e.g. long-lasting Vulcanian cycle). Second, we modelled and identified the potential syn-eruptive lahar impact areas on the northern sector of Vulcano, where residential and touristic facilities are located. We tested a range of parameters (e.g., entrainment capability, consolidation of tephra fallout deposit, friction angle) that can influence lahar propagation output both in terms of intensity of the event and extent of the inundation area. Finally, exposure and vulnerability surveys were carried out in order to compile exposure and risk maps for lahar-flow front velocity (semi-quantitative indicator-based risk assessment) and final lahar-deposit thickness (qualitative exposure-based risk assessment). Main outcomes show that the syn-eruptive lahar scenario with medium entrainment capability produces the highest impact associated with building burial by the final lahar deposit. Nonetheless, the syn-eruptive lahar scenario with low entrainment capacity is associated with higher runout and results in the highest impact associated with lahar-flow velocities. Based on our simulations, two critical infrastructures (telecommunication and power plant), as well as the main road crossing the island are exposed to potential lahar impacts (either due to lahar-flow velocity or lahar-deposit thickness or both). These results show that a risk-based spatial planning of the island could represent a valuable strategy to reduce the volcanic risk in the long term.

Highlights

  • Volcanic eruptions are associated with a variety of primary hazards, such as tephra fallout, Pyroclastic Density Currents (PDCs), toxic gas emissions and lava flows, as well as secondary hazards such as landslides, tsunamis and lahars

  • Quantifying the hazard and the risk associated with lahar inundation is complex

  • Multiple generation mechanisms, interactions with other phenomena and evolving rheological behaviour resulting from interactions with surfaces and topography during the flow represent as many parameters that require to be parameterized as input to numerical models

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Summary

Introduction

Volcanic eruptions are associated with a variety of primary hazards, such as tephra fallout, Pyroclastic Density Currents (PDCs), toxic gas emissions and lava flows, as well as secondary hazards such as landslides, tsunamis and lahars. All these hazards can strike settled areas. Gattuso et al Journal of Applied Volcanology (2021) 10:9 nearby active and dormant volcanoes at different spatial and temporal scales In this framework, lahars represent one of the most impactful volcanic hazards that can potentially strike areas up to hundreds of kilometres from active volcanoes and cause a high number of fatalities as demonstrated by the event that occurred in 1985 at Nevado del Ruiz volcano (Colombia) (Lowe et al 1986). Lahars can be produced either during or short after an eruption (syn-eruptive) and for years to decades after an eruption (post-eruptive) and have the potential to cause significant damage to buildings, public facilities, critical infrastructures as well as losses of human life and disruption to critical services (e.g. Sulpizio et al 2006; Wilson et al 2014; Jenkins et al 2015; Mead et al 2017)

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