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Heat loss measured at a lava channel and its implications for down-channel cooling and rheology

By
Andrew Harris
Andrew Harris
1
Hawaii Institute of Geophysics and Planetology (HIGP)–School of Ocean and Earth Science and Technology (SOEST), University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822, USA, and Instituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy
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John Bailey
John Bailey
2
Hawaii Institute of Geophysics and Planetology (HIGP)–School of Ocean and Earth Science and Technology (SOEST), University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822, USA
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Sonia Calvari
Sonia Calvari
3
Instituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy
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Jon Dehn
Jon Dehn
4
Alaska Volcano Observatory, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, Alaska 99775-7320, USA
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Published:
January 01, 2005

During May 2001 we acquired 2016 thermal images over an ∼8-h-long period for a section of active lava channel on Mount Etna (Italy). We used these to extract surface temperature and heat-loss profiles and thereby calculate core cooling rates. Flow surface temperatures declined from ∼1070 K at the vent to ∼930 K at 70 m. Heat losses were dominated by radiation (5 × 104 W m2) and convection (∼104 W/m2). These compare with a heat gain from crystallization of 6 × 103 W/m2. The imbalance between sinks and sources gives core cooling (δTx) of ∼110 K/km. However, cooling rate per unit distance also depends on flow conditions, where we distinguished: (1) unimpeded, high-velocity (∼0.2 m/s) flow with low δTx (0.3 K/m); (2) unimpeded, low-velocity (∼0.1 m/s) flow with higher δTx (0.5 K/m); (3) waning, insulated flow at low velocity (∼0.1 m/s) with low δTx (0.3 K/m); and (4) impeded flow at low velocity (<0.1 m/s) with higher δTx (0.4 K/m).

Our data allow us to define three thermal states of flow emplacement: insulated, rapid, and protected. Insulated is promoted by the formation of hanging blockages and coherent roofs. During rapid emplacement, higher velocities suppress cooling rates, and δTx can be tied to mean velocity (V mean) by δTx = a V mean −b. In the protected case, deeper, narrow channels present a thermally efficient channel, where δTx can be assessed using the ratio of channel width (w) to depth (d) in w/d = aδTx −b.

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GSA Special Papers

Kinematics and dynamics of lava flows

Michael Manga
Michael Manga
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Guido Ventura
Guido Ventura
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Geological Society of America
Volume
396
ISBN print:
9780813723969
Publication date:
January 01, 2005

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