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| Titel |
Modelling unsteady volcanic eruption columns and vulcanian eruption columns |
| VerfasserIn |
Matthew Scase, Peter Holland, Jeremy Phillips |
| 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 |
250047583
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| Zusammenfassung |
| The well-known steady model that describes the structure and composition of a volcanic
eruption column, due to Woods[1], has been coupled with the unsteady plume model of Scase
et al.[2] to produce a simple model capable of predicting the temporal evolution of unsteady
volcanic eruption columns[3]. The model is presented and is verified by comparison with data
taken from observations from one of the 7th February 2009 eruptions of Santiaguito (Caliente
Vent).
A steady model cannot be used to model a volcanic eruption whose conditions at the vent
have changed during the course of the eruption. That is to say that if the conditions that
produced the upper section of a volcanic eruption column no longer persist, no steady model
will be able to represent the eruption column – a full unsteady model is required. There
are numerous reasons why conditions at a volcanic vent may change during an
eruption, examples include; depletion of gas supply, caldera formation due to a
magma chamber collapse, compositional changes during the eruption, change in
height of the fragmentation level, erosion of the conduit on eruption time scales
etc.
One natural application for an unsteady eruption column model is to model vulcanian
eruptions. Typically these short-lived and often periodic eruptions peak in discharge
approximately 10–30 s after eruption, followed by a period of declining discharge. Flow rates
typically fall to negligible values within a time scale of hundreds of seconds from peak
discharge. The observed eruption of Santiaguito (Caliente Vent) on 7th Feb 2009 produced
such a vulcanian plume.
Field measurements were taken from the Santiaguito Volcano Observatory 6.3 km SSW of the
active Caliente dome. Simultaneous time series measurements of the gas and ash mass fluxes
were taken using a filtered UV camera[4]. Using these measurements as boundary condition
inputs for the unsteady eruption column model, along with standard values for atmospheric
and volcanic gas properties, the front position was predicted. The predicted position of the
front was compared with the observed position and the agreement was seen to be
good.
REFERENCES
[1]WOODS, A. W. 1988 The fluid dynamics and thermodynamics of eruption columns, Bull.
Volcanol., 50, 169—193.
[2]SCASE, M. M. 2009 Evolution of volcanic eruption columns, J. Geophys. Res. 114,
F04003.
[3]SCASE, M. M. et al. 2006 Time-dependent plumes and jets, J. Fluid Mech., 563,
443—461.
[4]YAMAMOTO, H., WATSON, I. W., PHILLIPS, J. C. & BLUTH, G. J. 2008 Rise dynamics
and relative ash distribution in vulcanian eruption plumes at Santiaguito Volcano,
Guatemala, revealed using an ultraviolet imaging camera, Geophys. Res. Lett., 35,
L08314. |
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