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| Titel |
Cooling Rate Profile of a Lava Flow |
| VerfasserIn |
F. W. von Aulock, B. Cordonnier, A. Ferk, K.-U. Hess, D. B. Dingwell, D. Richard |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019698
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| Zusammenfassung |
| The physical properties of lava flows are strongly influenced by the cooling rate. During rapid
heat loss, the structure of a melt undergoes a transition to a brittle behavior, referred to as the
glass transition temperature (Tg). Tg is dependent on the cooling rate. Field observations
commonly reveal that the cooling of a lava flow occurs by heat loss from the top and bottom.
This results in the boundaries of the flow cooling to Tg rapidly while the core of the
lava flow remains ductile and deforms readily. Thus, the thermal history of the
lava flow is an important factor in its emplacement, and data of the cooling rate is
necessary in understanding and predicting the length of the flow path. In this study, we
investigate the vertical cooling profile of a phonolitic lava flow (Tabonal Negro) in
Tenerife, Spain via a series of calorimetric analyses. Differential Scanning calorimeter
(DSC) measurements were performed on 14 natural glass samples to characterize the
rate at which the glass transition range was crossed. Specifically, the heat capacity
(Cp) was measured for different heating/cooling cycles to obtain a set of kinetic
parameters that were used to fit an initial Cp curve. Cooling rates ranging from
0.05 to 10 Kmin-1, and Tg (peak) between 874 K and 934 K were obtained.
As hypothesized, a gradient in cooling rates were observed, with the high rates
occurring at the margins of the flow. This gradient is far from symmetric along the
vertical cooling profile and exhibits a minimum at ~ 2∕3 of the flow thickness, seen
from the top. In a simplistic 1-dimensional model the cooling rate distribution is
reproduced, and a few basic scenarios have been tested to understand the thermal
history of the lava flow. The results of this model emphasize the importance of the
insulating properties of crust growth in a lava flow and it supports the calorimetric data. |
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