Volcanic edifice weakening via devolatilization reactions

Edifice instability, that can result in catastrophic flank collapse, is a fundamental volcanic
hazard. The subvolcanic basement can encourage such instability, especially if it is susceptible
to mechanical weakening by devolatilization reactions near magmatic temperatures. For this
reason, understanding how the physical and chemical properties of representative lithologies
deteriorate at high temperatures is potentially highly relevant for volcanic hazard mitigation.
This is particularly true for sedimentary rock, commonly found underlying volcanic edifices
worldwide, that undergo rapid deterioration even under modest temperatures.
Therefore, here we present the first experimental study of devolatilization reactions, induced
by magmatic temperatures, on sedimentary rock comprising a subvolcanic basement.
Our results show that, for a marly limestone representative of the basement at Mt Etna, devolatilization
reactions, namely the dehydroxylation of clay minerals and the decarbonation
of calcium carbonate, result in a dramatic reduction of mechanical strength and seismic velocities.
These temperature-driven reactions can promote volcanic instability at stresses much
lower than previously estimated.

Allard, P. et al., 2006. Mount Etna 1993–2005: anatomy of an evolving
eruptive cycle, Earth Sci. Rev., 78, 85–114.
Battaglia, M. et al., 2010. Dike emplacement and flank instability at Mount
Etna: constraints from a poro-elastic-model of flank collapse, J. Volc.
Geotherm. Res., 199, 153–164.
Bonaccorso, A. et al., 2010. Dike deflection modelling for inferring magma
pressure andwithdrawal, with application to Etna 2001 case, Earth planet.
Sci. Lett., 293, 121–129.
Borgia, A., Ferrari, L. & Pasquar`e G., 1992. Importance of gravitational
spreading in the tectonic and volcanic evolution of Mount Etna, Nature,
357, 231–235.
Borgia, A., Delaney, P.T. & Denlinger, R.P., 2000. Spreading volcanoes,
Annu. Rev. Earth planet. Sci., 28, 539–570.
Catalano, S., Torrisi, S. & Ferlito C., 2004. The relationship between late
Quaternary deformation and volcanism of Mt. Etna (eastern Sicily): new
evidence from the sedimentary substratum in the Catania region, J. Volc.
Geotherm. Res., 132, 311–334.
Civetta, L. et al., 2004. Thermal and geochemical constraints on the ‘deep’
magmatic structure of Mt. Vesuvius, J. Volc. Geotherm. Res., 133, 1–12.
Del Gaudio P. et al., 2010. Cooling rate-induced differentiation in anhydrous
and hydrous basalts at 500 MPa: implications for the storage and transport
of magmas in dikes, Chem. Geol., 270, 164–178.
Del Negro, C., Currenti, G. & Scandura, D., 2009. Temperature-dependent
viscoelastic modeling of ground deformation: application to Etna volcano
during the 1993–1997 inflation period, Phys. Earth planet. Inter., 172,
299–309.
Girard, J.-P. & Savin, S.M., 1996. Intracrystalline fractionation of oxygen
isotopes between hydroxyl and non hydroxyl sites in kaolinite measured
by thermal dehydroxylation and partial fluorination, Geochim. cosmochim.
Acta., 60, 469–486.
Heap,M.J., Vinciguerra, S. &Meredith, P.G., 2009. The evolution of elastic
moduli with increasing crack damage during cyclic stressing of a basalt
from Mt. Etna, Tectonophysics, 471, 153–160.
Heap, M.J. et al., 2011. Brittle creep in basalt and its application to timedependent
volcano deformation, Earth planet. Sci. Lett., 307, 71–82,
doi:10.1016/j.epsl.2011.04.035.
Lundgren, P. et al., 2004. Gravity and magma induced spreading of Mount
Etna volcano revealed by satellite radar interferometry, Geophys. Res.
Lett., 31, L04602, doi:10.1029/2003GL018736.
Merle, O., Barde-Cabusson, S.&vanWyk de Vries, B., 2010. Hydrothermal
calderas, Bull. Volcanol., 72, 131–147.
Molina, I. et al., 2005. Three-dimensional P-wave velocity structure of
Tungurahua Volcano, Ecuador, J. Volc. Geotherm. Res., 147, 144–156.
Mollo, S. et al., 2010a. Carbonate assimilation in magmas: a reappraisal
based on experimental petrology, Lithos, 114, 503–514.
Mollo S. et al., 2010b. Dependence of clinopyroxene composition on cooling
rate in basaltic magmas: implications for thermobarometry, Lithos, 118,
302–312.
Mollo, S. et al., 2011. Plagioclase-melt (dis)equilibrium due to cooling dynamics:
implications for thermometry, barometry and hygrometry, Lithos,
125, 221–235, doi:10.1016/j.lithos.2011.02.008.
Palchik, V., 1999. Influence of porosity and elastic modulus on uniaxial
compressive strength in soft brittle porous sandstones, Rock Mech. Rock
Eng., 32, 303–309.Palchik, V. & Hatzor, Y.H., 2004. The influence of porosity on tensile
and compressive strength of porous chalks, Rock Mech. Rock Eng., 37,
331–341.
Patan`e, D. et al., 2006. Time-resolved seismic tomography detects magma
intrusions at Mount Etna, Science, 313, 821–823.
Sack, R.O. & Ghiorso, M.S., 1994. Thermodynamics of multicomponent
pyroxenes: I. Formulation of a general model, Contrib. Mineral. Petrol.,
116, 277–286.
Samtani, M., Dollimore, D. & Alexander, K.S., 2002. Comparison of
dolomite decomposition kinetics with related carbonates and the effect
of procedural variables on its kinetic parameters, Thermochim Acta,
392–393, 135–145, doi:10.1016/S0040-6031(02)00094-1.
Siebert, L., 1992. Volcano hazards-threats from debris avalanches, Nature,
356, 658–659.
Siniscalchi, A. et al. 2010. Insights into fluid circulation across the Pernicana
Fault (Mt. Enta, Italy) and implications for flank instability, J. Volc.
Geotherm. Res., 193, 137–142.
Tibaldi, A.&Groppelli, G., 2002. Volcano-tectonic activity along structures
of the unstable NE flank of Mt. Etna (Italy) and their possible origin,
J. Volcanol. Geotherm. Res., 115, 277–302.
Tschegg, C., Ntaflos, T. & Hein I., 2009. Thermally triggered two-stage
reaction of carbonates and clay during ceramic firing: a case study on
Bronze Age Cypriot ceramics, Appl. Clay Sci., 43, 69–78.
Vinciguerra, S. et al., 2005. Relating seismic velocities, thermal cracking
and permeability in Mt. Etna and Iceland basalts, Int. J. Rock Mech. Min.
Sci., 42, 900–910.
van Wyk de Vries, B. & Borgia A., 1996. The role of basement in volcano
deformation, Geol. Soc. London Spec. Pub., 110, 95–110.
van Wyk de Vries, B. & Francis P.W., 1997. Catastrophic collapse at stratovolcanoes
induced by gradual volcano spreading, Nature, 387, 387–
390.
Wohletz, K., Civetta, L. & Orsi, G., 1999. Thermal evolution of the Phlegraean
magmatic system, J. Volc. Geotherm. Res., 91, 381–414.
Yavuz, H., Demirdag S. & Caran, S., 2010. Thermal effect on the physical
properties of carbonate rocks, Int. J. Rock Mech. Min. Sci., 47, 94–103.