HR: 17:15h
AN: V24A-06    [Abstracts]
TI: Plume Ascent Velocities Measured During Explosive Eruptions Using Thermal Infrared Thermometers
AU: * Harris, A
EM: harris@higp.hawaii.edu
AF: HIGP/SOEST, Univesity of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Ripepe, M
EM: mripepe@steno.geo.unifi.it
AF: DST, Universita di Firenze, via La Pira 4, Firenze, 50121 Italy
AU: Sahetapy-Engel, S
EM: sahetapy@soest.hawaii.edu
AF: HIGP/SOEST, Univesity of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Marchetti, E
EM: marchetti@geo.unifi.it
AF: DST, Universita di Firenze, via La Pira 4, Firenze, 50121 Italy
AU: Patrick, M
EM: patrick@higp.hawaii.edu
AF: HIGP/SOEST, Univesity of Hawaii, 1680 East-West Road, Honolulu, HI 96822 United States
AB: Emission and ascent velocities of plumes emitted during explosive volcanic events are important parameters for tracking, monitoring and modeling explosive eruptions. Such ascent velocities can be efficiently and routinely measured using thermal infrared thermometers in two ways. The first method uses two instruments targeted in sequence at fixed positions above the vent. Ascent velocity can then be obtained from the delay in response between the two instruments as the plume rises first through the lower field of view (FOV) and then through the higher FOV. The second uses a single instrument and uses the time taken for the signal to rise from background to maximum. Assuming that this represents the time (t) that the plume leading edge takes to rise through a FOV of known height (h), then velocity is obtained simply from h/t. Using data collected at Stromboli (Italy) and Santiaguito (Guatemala) during 2002-2003 we compare the thermally-derived ascent velocities with independently (e.g. video) derived velocities. We find that the second approach is easier to set-up, and less prone to error. During normal strombolian at Stromboli, we obtain (at-vent) ascent velocities of 3-100 m/s, with a mean of around 20 m/s. We obtain a similar range for ash-dominated emissions ascending to around 1 km at Santiaguito, where ascent velocities of around 20 m/s are typical. Highest velocities were obtained during the 5 April 2003 paroxysm at Stromboli where a thermally derived maximum ejection velocity of 320 m/s compares with the velocity of 310 m/s required to explain the travel time for a block that landed very close to one of our seismic stations.
DE: 8400 VOLCANOLOGY
DE: 8428 Explosive volcanism
DE: 8485 Remote sensing of volcanoes
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005