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| Titel |
Modelling the 1982 and 2000 channelised lava flows at Mt Cameroon Volcano using FLOWGO thermo-rheological model |
| VerfasserIn |
M. Wantim, M. Kervyn, G. G. J. Ernst, C. E. Suh, P. Jacobs, M.-A. del Marmol |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060253
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| Zusammenfassung |
| Like many other effusive volcanoes, Mount Cameroon is a volcano for which only limited
information exist on the properties and emplacement dynamics of recent lava flows. Limited
accessibility of remote eruption sites together with the lack of monitoring equipment make it
difficult to carry out on-site rheologic measurements during eruptions. This study is
based on field documentation of the morphometry of historical lava flows at Mt
Cameroon, e.g. channel geometry (width and depth), levee and background slope, in
order to derive the lava yield strength, velocity and effusion rate. Lava density and
viscosity were calculated from compositional data and using laboratory methods.
This first phase enabled us to constrain quantitatively the rheological and dynamic
characteristics of lava flow effusion for the 1982 and 2000 Mt Cameroon eruptions. These
parameters served as input to calibrate the FLOWGO thermo-rheological model. This 1D
physical model is aimed at modelling the down-flow evolution of the temperature,
geometry and rheology of channel-contained cooling limited lava flows. To account for
the uncertainty in the input rheological and geometrical data, three end-member
scenarios were used to bracket the potential range in lava channel initial dimension,
initial lava temperature and phenocryst content. For each of these scenarios, two
crustal growth models were used one assuming a strong insulation due to lava flow
surface crusting, the other a much lower rate of lava surface crusting. A total of 12
simulations were made per flow and the results were compared against the channel
geometry, microlite content and yield strength and viscosity estimates at different
distance from the vent derived from field and laboratory analyses. Best-fit models
where obtained for both the 1982 and 2000 lava flows using a low rate of surface
crusting, a high initial temperature and a low phenocryst content. Model-predicted
lengths were within 95% of the actual lengths. Both modelled viscosity (102 –
104 Pa s) and yield strength (103 – 104 Pa) increased down flow consistently with
morphometry-based estimates. Modelled mean effusion rates for the 1982 (52 - 64 m3 s-1)
and 2000 (10 m3 s-1) flows closely matched field calculations (30-70 and 17.5 m3s-1
respectively). Heat loss due to radiation (Qrad;105 – 107 Wm-1) was the dominant heat
loss process. FLOWGO model was however unable to reproduce the near-vent
increase in microlite content, probably related to lava temperature decrease caused
by rapid flow degassing after extrusion. Sensitivity analyses using the 1982 lava
flow showed that flow length is greatly sensitive to input channel dimension and
initial volume fraction of phenocrysts. The volume fraction of phenocrysts was
observed to have an effect on velocity, flow length and effusion rate producing
shorter flows as the percentage of phenocrysts increased. The calibration of the
FLOWGO model is a first step towards a lava flow hazard assessment at Mt Cameroon. |
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