Thermal characterization of the Vulcano fumarole field |
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Authors: | Andrew J L Harris Luigi Lodato Jonathan Dehn Letizia Spampinato |
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Institution: | (1) HIGP/SOEST, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, USA;(2) Istituto Nazionale di Geofisica e Vulcanologia—Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy;(3) University of Alaska Fairbanks, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 9775–7320, USA |
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Abstract: | Ground-based thermal infrared surveys can contribute to complete heat budget inventories for fumarole fields. However, variations
in atmospheric conditions, plume condensation and mixed-pixel effects can complicate vent area and temperature measurements.
Analysis of vent temperature frequency distributions can be used, however, to characterise and quantify thermal regions within
a field. We examine this using four thermal infrared thermometer and thermal image surveys of the Vulcano Fossa fumarole field
(Italy) during June 2004 and July 2005. These surveys show that regions occupied by low temperature vents are characterised
by distributions that are tightly clustered around the mean (i.e., the standard deviation is low), highly peaked (positive
kurtosis) and skewed in the low temperature direction (negative skewness). This population is associated with wet fumaroles,
where boiling controls maximum temperature to cause a narrow distribution with a mode at 90–100°C. In contrast, high temperature
vent regions have distributions that are widely spread about the mean (i.e., the standard deviation is high), relatively flat
(negative kurtosis) and skewed in the high temperature direction (positive skewness). In this dry case, fumaroles are water-free
so that maximum temperatures are not fixed by boiling. As a result greater temperature variation is possible. We use these
results to define two vent types at Vulcano on the basis of their thermal characteristics: (1) concentrated (localized) regions
of high temperature vents, and (2) dispersed low temperature vents. These occur within a much larger region of diffuse heat
emission across which surfaces are heated by steam condensation, the heat from which causes elevated surface temperatures.
For Vulcano's lower fumarole zone, high and low temperature vents occupied total areas of 3 and 6 m2, respectively, and occurred within a larger (430 m2) vent-free zone of diffuse heat emission. For this lower zone, we estimate that 21–43 × 103 W of heat was lost by diffuse heat emission. A further 4.5 × 103 W was lost by radiation from high temperature vents, and 6.5 × 103 W from low temperature vents. Thus, radiative heat losses from high and low temperature vents within Vulcano's lower fumarole
zone respectively account for 10% and 15% of the total heat lost from this zone. This shows that radiation from open vents
can account for a non-trivial portion of the total fumarole field heat budget. |
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Keywords: | Fumarole Vulcano Thermal image Infrared thermometer Heat flux |
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