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| Titel |
Volcanic edifice weakening via thermal reactions |
| VerfasserIn |
Sergio Vinciguerra, Michael Heap, Silvio Mollo, Yan Lavallée, Kai Hess, Donald Dingwell, Gianluca Iezzi, Patrick Baud |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051922
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| Zusammenfassung |
| Edifice instability, that can result in catastrophic flank collapse, is a fundamental volcanic
hazard. The sub-volcanic basement can encourage such instability, especially if it is
susceptible to reactions generating thermal decomposition near magmatic temperatures. For
this reason, understanding how the physical and chemical properties of sub-volcanic
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. Here we present the first experimental study of thermo-chemical reactions,
induced by magmatic temperatures, on a range of sedimentary rocks from a sub-volcanic
basement.
Here we present the results of an experimental study on three different limestones found
within the subvolcanic basement at Mt. Etna, Italy. The three limestones are (1) Thala
limestone (19% porosity, 73-22 calcite-dolomite ratio), (2) Mt. Climiti limestone (32%
porosity, 100% calcite) and (3) a marly limestone (6.5% porosity, 75% calcite, 15% quartz
and 10% kaolinite). Our study demonstrates that, at temperatures of 800Ë C, the carbonate in
the samples is completely dissociated, resulting in a loss of about 45% mass (for the two
purer limestones) and about 35% for the marly limestone. Secondary phases, such as
portlandite, lime and periclase, form at these high temperatures. These debilitating chemical
changes have a dramatic influence on the physical properties of the investigated
limestones. Porosity, dynamic Poisson’s ratio and theV p-V s ratio all show a substantial
increase, whilst P- and S-wave velocities and dynamic Young’s modulus all show a
substantial decrease. Although total changes in physical properties are less for the marly
limestone, likely to be the result of its lower carbonate content, it shows greater
physical property degradation at lower temperatures, due to the dehydroxylation of
kaolinite.
We suggest that these changes in physical properties can help explain (1) the
increased edifice instability seen to follow magmatic events, (2) the anomalously low
seismic velocity zone present within the sub-volcanic sedimentary basement, (3) the
anomalously high CO2 degassing and the conflict between the calculated magma volume
at depth (using CO2 emissions) and the volume of erupted magma, and (4) the
anomalously high V p-V s ratios and the rapid migration of fluids. The data also
suggest that care must be taken when selecting elastic parameters (1) to model ground
deformation at an edifice, (2) for the calibration of damage mechanics criteria,
and (3) when applying simple failure criteria to studies of volcano flank stability. |
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