Publication Date:
2020-11-17
Description:
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.
Description:
Published
Description:
441
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
JCR Journal
Description:
reserved
Keywords:
Fumarole
;
Vulcano
;
Thermal image
;
Infrared thermometer
;
Heat flux
;
04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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