Lahar risk assessment from source identification to potential impact analysis: the case of Vulcano Island, Italy

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.

­­Dynamics of rain-triggered lahars and destructive power inferred from seismo-acoustic arrays and time-lapse camera correlation at Volcán de Fuego, Guatemala.

“…Due to the complexity and variability of flow behaviors, lahars are challenging to model. Diverse modeling approaches, from empirical to physics-based, have been used to determine lahar flow behaviors (e.g., Manville et al 2013;Córdoba et al 2015;Jones et al 2015;Dille et al 2020), however, even many of the probabilistic models have several limitations, as the importance of damaging components of lahar flows (e.g., velocity, depth and density) can vary wildly between lahar flows Gattuso et al 2021). Therefore, deterministic parameters continue to be useful in facilitating our understanding of internal flow dynamics and the overall required inputs for more robust and accurate probabilistic models.…”

Assessing the effectiveness and the economic impact of evacuation: the case of the island of Vulcano, Italy

“…exponential hazard function (Ho, 1992;Cornelius and Voight, 1994;Chastin and Main, 2003;Connor et al, 2003;De la Cruz-Reyna and Reyes-Dávila, 2001). The spatial exposure of evacuees can also be determined based on the probability of being impacted by an eruption using the models of Aucker et al ( 2013) and Brown et al (2017) as well as hazard analyses of Vulcano (Dellino et al, 2011;Biass et al, 2016a, b;Bonadonna et al, 2021;Gattuso et al, 2021). The probability of being impacted by various volcanic hazards depends on eruption dynamics (i.e.…”

“…wind speed and direction). Hazard maps for Vulcano exist that describe the potential extent and intensity of tephra fallout and ballistic projectiles (Biass et al, 2016a, b), PDCs (Dellino et al, 2011) and lahars (Gattuso et al, 2021). However, given that before the actual eruption (phreatic or magmatic) takes place, the extent and intensity of the associated hazards are not known, we consider here the evacuation of certain areas to be based on the worst-case scenario, e.g.…”

Modelling Erosion and Floods in Volcanic Environment: The Case Study of the Island of Vulcano (Aeolian Archipelago, Italy)

“…These events have been described by Ferrucci et al [14] as erosion-dominated events, with the generation of small volume debris flows that transfer loose material downslope, producing a denudation of the substratum upslope (made up of Varicoloured Tuffs), on which a stable rill network develops. Recently, the works of Baumann et al [35] and Gattuso et al [36] have focused on the characterization of materials and on hazard assessment related to syn-and post-eruptive debris flows. These works take into consideration the triggering and transport of material deriving from future eruptions, taking into account short and long-lasting eruptive scenarios deriving from Biass et al [37], but do not consider the phenomena of erosion and flooding that occur during inter-eruptive periods, such as that post-1890.…”