Publication Date:
2017-04-04
Description:
Many volcanic edifices are subject to flank failure, usually produced by a combination of events, rather than
any single process. From a dynamic point of view, the cause of collapse can be divided into factors that
contribute to an increase in shear stress, and factors that contribute to the reduction in the friction coefficient
μ of a potential basal failure plane. We study the potential for flank failure at Mount Etna considering a
schematic section of the eastern flank, approximated by a wedge-like block. For such geometry, we perform a
(steady state) limit equilibrium analysis: the resolution of the forces parallel to the possible basal failure plane
allows us to determine the total force acting on the potentially unstable wedge. An estimate of the relative
strength of these forces suggests that, in first approximation, the stability is controlled primarily by the
balance between block weight, lithostatic load and magmatic forces. Any other force (sea load, hydrostatic
uplift, and the uplift due to mechanical and thermal pore-fluid pressure) may be considered of second order.
To study the model sensitivity, we let the inferred slope α of the basal surface failure vary between −10° and
10°, and consider three possible scenarios: no magma loading, magmastatic load, and magmastatic load with
magma overpressure. We use error propagation to include in our analysis the uncertainties in the estimates of
the mechanics and geometrical parameters controlling the block equilibrium. When there is no magma
loading, the ratio between destabilizing and stabilizing forces is usually smaller than the coefficient of friction
of the basal failure plane. In the absence of an initiating mechanism, and with the nominal values of the
coefficient of friction μ=0.7±0.1 proposed, the representative wedge will remain stable or continue to move
at constant speed. In presence of magmastatic forces, the influence of the lateral restraint decreases. If we
consider the magmastatic load only, the block will remain stable (or continue to move at constant speed),
unless the transient mechanical and thermal pressurization significantly decrease the friction coefficient,
increasing the instability of the flank wedge for αN5° (seaward dipping decollement). When the magma
overpressure contribution is included in the equilibrium analysis, the ratio between destabilizing and
stabilizing forces is of the same order or larger than the coefficient of friction of the basal failure plane, and the
block will become unstable (or accelerate), especially in the case of the reduction in friction coefficient.
Finally, our work suggests that the major challenge in studying flank instability at Mount Etna is not the lack of
an appropriate physical model, but the limited knowledge of the mechanical and geometrical parameters
describing the block equilibrium.
Description:
This work was funded by Istituto Nazionale di
Geofisica e Vulcanologia (INGV) and the Italian Dipartimento per la
Protezione Civile (DPC) (DPC-INGV project V4 “Flank”).
Description:
In press
Description:
1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
Description:
3.2. Tettonica attiva
Description:
3.6. Fisica del vulcanismo
Description:
4.3. TTC - Scenari di pericolosità vulcanica
Description:
JCR Journal
Description:
reserved
Keywords:
Etna
;
dike intrusion
;
flank instability
;
poro-elasticity
;
analytical modelling
;
04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
;
04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
;
04. Solid Earth::04.04. Geology::04.04.09. Structural geology
;
04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous
;
04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
;
04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
;
04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
;
05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous
;
05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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