Failure of volcano slopes

Abstract

Magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse. Their role is twofold, involving both driving and resisting forces. First, flank stability is diminished by magmastatic and magma overpressures, and steepened slopes, that accompany intrusion. Second, excess pore pressures in potential failure zones can be generated as a result of intrusion-related mechanical or thermal straining of the rock-fluid medium, pressurized retrograde boiling in high level magma chambers, or hydrothermal fluid circulation. Also, earthquakes may aid collapse through inertial forces and shaking-induced pore pressure generation. These excess pore pressures reduce the sliding resistance, as shown for wedge-shaped slide blocks for selected cases. The destabilizing influence of mechanically induced pore pressures is maximized as the intruded width, or corresponding overpressure, of the intrusion is increased. The destabilizing influence of thermally induced pore pressures is conditioned by the severity of thermal forcing, ratios of thermal and hydraulic diffusivities, and the time required for the fluid pressure disturbance to propagate outwards from the intrusion. Retrograde boiling and hydrothermal circulation overpressure mechanisms may be evaluated by similar models. Failure initiation does not imply sustained failure; in some cases, enhancement of pore pressures through deviatoric shearing, frictional heating, or runout over compressible saturated alluvium or marine sediments may be necessary following slide initiation to maintain the impetus of flank failure for long runout. Models are examined for oceanic volcanoes of shallow flank inclination and for terrestrial composite volcanoes with considerably steeper flanks. Les intrusions magmatiques peuvent provoquer et entretenir l'effondrement massif et catastro-phique d'un volcan. Elles le font en faisant intervenir à la fois des forces d'entraînement et des forces de résistance. Pour commencer, les surpressions magmastatiques et magmatiques et l'accentuation des pentes qui accompagnent l'intrusion réduisent la stabilitè des versants. Deuxièmement, la pression des pores pent devenir excessive dans les zones d'effondrement potentiel sous l'effet des contraintes mécaniques ou thermiques imposées au milieu roche-fluide par l'intrusion, du bouillonnement rétrograde sous pression dans les réservoirs de magma de haut niveau, ou de la circulation du liquide hydrothermal. Les séismes peuvent, eux aussi, contribuer à l'effondrement en produisant des forces d'inerde et des secousses qui font augmenter la pression des pores. L'excès de pression réduit la résistance au glissement, comme le montrent les exemples de blocs de glissement en coin illustrés dans Particle. Plus l'intrusion est large ou plus la surpression correspondante est forte, plus Paugmentation mécanique de la pression des pores a un effet déstabilisant. L'effet déstabilisant de Paugmentation thermique de la pression des pores dépend de l'importance du refoulement thermique, des ratios de diffusivité thermique et hydraulique, et du temps de propagation de Paugmentation de pression. On pent utiliser des modéles semblables pour évaluer le bouillonnement rétrograde et les mécanismes de surpression de la circulation hydrothermale. L'amorce d'un effondrement n'est pas nécessairement suivie d'un effondrement entretenu: dans certains cas, Peffondrement des versants, une foisamorcé, ne pent se poursuivre que si la pression des pores augmente sous Peffet d'un cisaillement déviateur, d'un réchauffement produit par frottement, ou d'un écoulement sur des alluvions ou des sédiments marins saturés et compressibles. Let auteurs examinent des modèles pour des volcans océaniques à pentes faibles et pour des volcans terrestres composites à versants bien plus raides.

Multiple edifice failures, debris avalanches and associated eruptions in the Holocene history of Shiveluch volcano, Kamchatka, Russia

“…Structural factors, such as steep dip slopes with interbedded fractured lava flows and unconsolidated pyroclastic materials, high water tables, extensive hydrothermal alteration in areas surrounding the central conduit, and abnormal pore-fluid pressures, are recognised as significant factors (Voight et al 1981(Voight et al , 1983Siebert 1984Siebert , 1996Voight and Elsworth 1997). Most high volcanic edifices appear relatively weak in general, but relative weakness alone is insufficient for large-scale failure.…”

“…Failures of Shiveluch and of other volcanoes show that many collapse events are strongly correlated with magmatic eruptions (Siebert 1984(Siebert , 1996Belousov and Belousova 1996;Voight and Elsworth 1997). Thus, disturbance of the edifice by some process that accompanies the magmatic eruption is a primary reason for most large-scale edifice failures.…”

Relating seismic velocities, thermal cracking and permeability in Mt. Etna and Iceland basalts

“…The high level of mechanical and thermal stresses acting in volcanic areas, along with circulation of fluids at high temperatures, are believed to enhance mechanical damage of the host rocks to cyclic magmatic pressurisations, leading to the failure of rocks over extended periods of time at stresses far below their short-term failure stress, through mechanisms such as stress corrosion crack growth [2]. The physical state of the host rock has been recognised as crucial in determining preferential penetration of magma or steam in local fractures [3], hydrofracturing by magma injection, development of shear zones during indentation [4], and the response to the pressurization of fluids within the rock matrix [5,6]. Magmatic pressure distributions and edifice failure episodes will then depend on a high number of variables, given by the size, orientation, degree of alignment, aspect ratio and, importantly, fluid content; and from the micro to the macro scale.…”

Alteration, slope-classified alteration, and potential lahar inundation maps of volcanoes for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Volcano Archive

“…Internal stressors such as pore fluid pressure and magmatic intrusions such as cryptodomes and (or) accompanying eruptions of overlying lava flows and pyroclastic deposits need to be considered as well (Voight and Elsworth, 1997;van Wyck de Vries and Francis, 1997;van Wyck de Vries and others, 2000;others, 2000, 2006). Wedge collapse models such as SCOOPS have been used to determine volumes of flank collapse materials using the parameters described above (Reid and others, 2000;Reid and others 2006).…”