Bruno Faria

Multiparameter monitoring of Fogo Island, Cape Verde, for volcanic risk mitigation

Fogo Island in the Cape Verde Archipelago (North Atlantic) is a stratovolcano of nearly conical shape that rises 2829 m above sea level and V6000 m above the surrounding seafloor. With a population of 40 000, the island has known intense historical volcanic activity since AD 1500, with an average interval between eruptions of the order of 20 years. Twentieth-century rates were more subdued, with only two flank eruptions in 1951 and 1995. Following the 1995 eruption, increased awareness of the volcanic hazard affecting the population of the island led to the deployment of the permanent VIGIL Network. Seismographic stations (both broadband and short-period), tiltmeters and a CO2 sensor where installed in Fogo, together with a telemetry infrastructure to allow remote real-time monitoring. A broadband seismographic station was installed in neighbour Brava Island. The operation of the network was complemented by the introduction of routine geodetic and microgravity surveying and the operation of an automatic meteorological station. In this paper, we describe the methodology adopted to monitor the volcanic activity, combining real-time data analysis (volcanotectonic and volcanic earthquakes, volcanic tremor and tilt) with repeated surveying at intervals of several months (GPS, microgravity). Examples of data from the first years of operation are presented. In particular, the data pertaining to a period of anomalous activity in September^October 2000 are discussed, in the context of the risk mitigation strategy currently being developed.

Damage from lava flows: insights from the 2014–2015 eruption of Fogo, Cape Verde

Fast-moving lava flows during the 2014–2015 eruption of Fogo volcano in Cape Verde engulfed 75% (n = 260) of buildings within three villages in the Chã das Caldeiras area, as well as 25% of cultivable agricultural land, water storage facilities and the only road into the area. The eruption had a catastrophic impact for the close-knit communities of Chã, destroying much of their property, land and livelihoods. Volcanic risk assessment typically assumes that any object - be it a building, infrastructure or agriculture - in the path of a lava flow will be completely destroyed. Vulnerability or fragility functions for areas impacted by lava flows are thus binary: no damage in the absence of lava and complete destruction in the presence of lava. A pre-eruption field assessment of the vulnerability of buildings, infrastructure and agriculture on Fogo to the range of volcanic hazards was carried out in 2010. Many of the areas assessed were subsequently impacted by the 2014–2015 eruption and, shortly after the eruption ended, we carried out a post-eruption field assessment of the damage caused by the lava flows. In this paper, we present our findings from the damage assessment in the context of building and infrastructural vulnerability to lava flows. We found that a binary vulnerability function for lava flow impact was appropriate for most combinations of lava flow hazard and asset characteristics but that building and infrastructure type, and the flow thickness, affected the level of impact. Drawing on these observations, we have considered potential strategies for reducing physical vulnerability to lava flow impact, with a focus on buildings housing critical infrastructure. Damage assessments for lava flows are rare, and the findings and analysis presented here are important for understanding future hazard and reconstruction on Fogo and elsewhere.

Atomistic Simulations of Carbon Nanotubes: Stiffness, Strength, and Toughness of Locally Buckled CNTs

Abstract In this chapter, the atomistic simulation of carbon nanotubes (CNTs) is presented and their behavior (stiffness, strength, and toughness) under local deformation is investigated by taking into account the contributions of the authors to the current state of the art. First, the atomistic modeling of CNTs is described and the three most adopted methods are briefly addressed. One of these, molecular dynamics (MD), is then explained in more detail (the selection of potentials and time integration scheme). After that, three main topics are addressed: (1) the suitability of continuum shell models to simulate the nanotube behavior (in comparison with MD), (2) the influence of combined shortening–twisting on the local buckling behavior of nanotubes, and (3) the chirality and anisotropic effects in nanotubes. Several illustrative examples are shown and attention is focused on the MD results, namely, the nanotube stiffness, strength, and toughness. Then, some final remarks and future developments are drawn.

Influence of Bond Kinematics on the Rupture of Non-Chiral CNTs under Stretching–Twisting

This chapter focuses on the role played by bond kinematics in the collapse behaviour of armchair and zig-zag CNTs under combined stretching-twisting. The analyses are performed through MD simulations, using LAMMPS code with the built-in potential AIREBO for C–C bonds. Incremental combinations of stretching displacements and twisting rotations are imposed to the CNT end atoms. The results are first analyzed in the form of diagrams of energy at rupture versus the twisting-to-stretching rate and diagrams of interaction between the axial stretching displacement at rupture and the angle of twist at rupture. A detailed study on the variation of bond length and angle amplitude with the imposed stretching and twisting deformations is shown. The case of pure stretching is first described, as a reference case. Two combined twisting-stretching cases and the pure twisting case are dealt with separately for zig-zag and armchair CNTs. It is concluded that two kinematic mechanisms influence the rupture of CNTs: one is the bond elongation for low twisting-to-stretching rate and other is the hexagonal cell distortion for moderate to high twisting-to-stretching rate.