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|Authors: ||Harris, A. J. L.*|
|Title: ||Heat loss measured at a lava channel and its implications for down-channel cooling and rheology|
|Issue Date: ||2005|
|Keywords: ||lava channel|
|Abstract: ||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 profi les 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 (δT/δx) of ~110 K/km. However, cooling
rate per unit distance also depends on fl ow conditions, where we distinguished:
(1) unimpeded, high-velocity (~0.2 m/s) fl ow with low δT/δx (0.3 K/m); (2) unimpeded,
low-velocity (~0.1 m/s) fl ow with higher δT/δx (0.5 K/m); (3) waning, insulated fl ow at
low velocity (~0.1 m/s) with low δT/δx (0.3 K/m); and (4) impeded fl ow at low velocity
(<0.1 m/s) with higher δT/δx (0.4 K/m).
Our data allow us to defi ne three thermal states of fl ow 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 δT/δx can be tied to mean velocity (Vmean) by δT/δx = aVmean
–b. In the protected
case, deeper, narrow channels present a thermally effi cient channel, where δT/δx can
be assessed using the ratio of channel width (w) to depth (d) in w/d = aδT/δx–b.|
|Appears in Collections:||Book chapters|
04.08.06. Volcano monitoring
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