Publication Date:
2017-04-04
Description:
An open channel lava flow on Mt. Etna (Sicily)
was observed during May 30–31, 2001. Data collected using
a forward looking infrared (FLIR) thermal camera and
a Minolta-Land Cyclops 300 thermal infrared thermometer
showed that the bulk volume flux of lava flowing in
the channel varied greatly over time. Cyclic changes in the
channel’s volumetric flow rate occurred over several hours,
with cycle durations of 113–190 min, and discharges peaking
at 0.7 m3 s−1 and waning to 0.1 m3 s−1. Each cycle
was characterized by a relatively short, high-volume flux
phase during which a pulse of lava,with awell-defined flow
front, would propagate down-channel, followed by a period
of waning flow during which volume flux lowered. Pulses
involved lava moving at relatively high velocities (up to
0.29 m s−1) and were related to some change in the flow
conditions occurring up-channel, possibly at the vent. They
implied either a change in the dense rock effusion rate at the
source vent and/or cyclic-variation in the vesicle content of
the lava changing its bulk volume flux. Pulses would generally
overspill the channel to emplace p¯ahoehoe overflows. During periods of waning flow, velocities fell to 0.05 m
s–1. Blockages forming during such phases caused lava to
back up. Occasionally backup resulted in overflows of slow
moving ‘a‘¯a that would advance a few tens of meters down
the levee flank. Compound levees were thus a symptom
of unsteady flow, where overflow levees were emplaced
as relatively fast moving p¯ahoehoe sheets during pulses,
and as slow-moving ‘a‘¯a units during backup. Small, localized
fluctuations in channel volume flux also occurred
on timescales of minutes. Volumes of lava backed up behind
blockages that formed at constrictions in the channel.
Blockage collapse and/or enhanced flow under/around the
blockage would then feed short-lived, wave-like, downchannel
surges. Real fluctuations in channel volume flux,
due to pulses and surges, can lead to significant errors in
effusion rate calculations.
Description:
Published
Description:
497-515
Description:
reserved
Keywords:
Etna
;
FLIR
;
Lava channel
;
a‘a
;
Thermal
;
Unsteady flow
;
Morphology
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
1750933 bytes
Format:
application/pdf
Permalink
