HR: 0800h
AN: V31E-0718    [Abstracts]
TI: The Dynamics of Explosions at Santiagutio Volcano, Guatemala
AU: Scharff, L
EM: lea.scharff@zmaw.de
AF: Inst.\ of Geophysics, University of Hamburg, Bundesstr.\ 55, Hamburg, HH 20146, Germany
AU: Gerst, A
EM: alexander.gerst@zmaw.de
AF: Inst.\ of Geophysics, University of Hamburg, Bundesstr.\ 55, Hamburg, HH 20146, Germany
AU: * Hort, M
EM: matthias.hort@zmaw.de
AF: Inst.\ of Geophysics, University of Hamburg, Bundesstr.\ 55, Hamburg, HH 20146, Germany
AU: Johnson, J B
EM: jeff.johnson@ees.nmt.edu
AF: Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorrow, NM 87801, United States
AB: Dynamic processes and explosive activity at dacitic volcanoes that are erupting viscous magma is still a matter of intense research, not the least because such volcanoes produce violent explosions. Here we present Doppler radar observations recorded between Jan.\ 8 and Jan.\ 13 2007 during a multidisciplinary experiment at Santiaguito volcano, Guatemala. The experiment comprised velocities and density of the erupted material (Doppler radar, Univ.\ Hamburg), infrasound and high speed video data (Univ.\ of New Hampshire), seismic recordings (Univ. of New Hampshire and Univ.\ of North Carolina), and temperatures of the dome and eruption column (infrared camera, Univ.\ de Colima). The instruments, operating on a direct line of sight (video, thermal imager, and Doppler radar), were installed on the top of Santa Maria volcano, and were pointed down (inclination 27°) towards the active Caliente lava dome 1200 m below and 2600 m distant. During the observational period we recorded a total of 142 explosions from the dome with the Doppler radar. Here we focus on the Doppler radar data to characterize the different types of explosions. The radar transmits 50mW of power at a frequency of 24GHz enabling us to see particles down to a size of mm even at low concentrations. The data are processed such that we get information on the amount of energy reflected by the particles in the radar beam as a function of the velocity. Because the approximate field of view of the radar beam is 1.6 deg (70m width at the target distance) and covers only a portion of the 200 m wide dome, the orientation of the beam was changed several times during the experiment to observe different portions of the dome exhibiting different eruptive processes. Many of the pyroclastic explosions appeared to emanate from concentric ring shaped fractures comprising an inner and/or an outer ring on the dome. While focused on the center of the dome, we find that the explosions start with very low velocities (\<4m/s), indicating a slow uplift proceeding the main part of an explosion by up to 25s, and before activity can be detected by eye. This slow movement appears to be corroborated by examining high resolution video images of the dome just prior to pyroclastic emissions. Significantly higher velocities (~60m/s) mark the onset of the main phase of the explosion. Most of the explosions are very gas rich, and carry only small amounts of ash. This is deduced from the relatively low reflected energy when targeting the rising eruption clouds above the dome. Another type of explosion is observed when pointing the radar at the outer ring of the dome. Here we find that some of the explosions show two explosions following each other within 30 to 50s. Similar eruption characteristics were observed with the other observation methods, where especially high speed video footage proved as a valuable complement to the radar data.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8428 Explosive volcanism
DE: 8485 Remote sensing of volcanoes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting