Explosion mechanisms at Arenal volcano, Costa Rica: An interpretation from integration of seismic and Doppler radar data

Abstract

[1] We execute an integrated analysis of broadband seismic and Doppler radar data to gain insights into the subsurface mechanisms that drive repetitive, mildly explosive activity of Arenal volcano (Costa Rica). We find large variability of both seismic and radar waveforms, and nonsystematic relationships between the two. Seismic recordings display long-lasting tremor sequences and numerous explosion quakes. Radar measurements show that tephra emissions are poorly correlated, in both time and energy, to the seismic activity. Tephra emissions were found in association with explosion quakes but also during episodes of tremor and seismic quiescence. Moreover, the exit velocity, mass loading, and kinetic energy of the emissions show no clear relationship with the coeval seismic amplitude and frequency content. We propose a conceptual source model whereby degasing is controlled by opening and closing of fractures that crosscut a rigid cap atop the conduit. When the fracture's strength is overcome by the gas pressure building up below, it suddenly opens and high-velocity gas escapes, producing high-frequency elastic waves typical of explosion quakes. Gas release also occurs in relation to periodic opening and closure of the fractures to produce repetitive pressure pulses, this being the source of tremor. In both cases, varying quantities of fragmented material may be carried by the gas, which can be detected by the radar if their concentration is high enough. Moreover, the highly variable, constantly changing state of lava cap (e.g., thickness, fracture network and gas permeability) results in nonrepeatable source conditions and explains the complex relationship between tephra emissions and associated seismic signals.

Array analysis of the seismic wavefield of long‐period events and volcanic tremor at Arenal volcano, Costa Rica

“…This conclusion agrees with most studies of LP events at Arenal volcano that hint to a shallow source located a few hundred meters below the summit craters [ Alvarado et al , ; Hagerty et al , ; Lesage et al , ; Davi et al , ; Valade et al , ]. Explosion quakes with acoustic phases are assumed to be very shallow, while LP events are slightly deeper [ Valade et al , ].…”

Quantifying unsteadiness and dynamics of pulsatory volcanic activity

“…Data acquisition uncertainty considered as the absolute error. References: (1) Hill et al (1998), (2) INGV (2012), (3) Ripepe et al (2013), (4) Sahetapy-Engel et al (2008), (5) Iguchi (2013), (6) Druitt et al (2002), (7) Ruiz et al (2005), (8) Varley et al (2006), (9) Webb et al (2014), (10) Watt et al (2007), (11) Dirksen et al (2006), (12) Valade et al (2012), (13) Ripepe et al (2008 Unfortunately, this complexity is not encompassed by current classification schemes as they are mostly based on deposit properties, e.g. tephra dispersal, grainsize and/or erupted volume, with the assumption of steady-state conditions (e.g.…”

Pulsed Vulcanian explosions: A characterization of eruption dynamics using Doppler radar

“…Pulsed release of tephra and gas has been observed at volcanoes like Etna (Italy; pulse periods of 1.8 s [Tazieff, 1970] and 3.8-5.5 s [Dubosclard et al, 2004]), Stromboli (Italy; Scharff et al, 2008; 0.2-3 s [Taddeucci et al, 2012]), Yasur (Vanuatu; 0.5-3 s [Gaudin et al, 2014]), and Arenal volcano (Costa Rica; 3 s [Donnadieu, 2012;Valade et al, 2012]). Pulses have also been observed during Vulcanian eruptions at Galeras (Colombia; Stix et al, 1997) and Cordón Caulle (Chile; Schipper et al, 2013), yet a systematic study of the timing of such pulses has not been carried out.…”