Articles | Volume 8, issue 3
Solid Earth, 8, 697–719, 2017
Solid Earth, 8, 697–719, 2017

Research article 23 Jun 2017

Research article | 23 Jun 2017

Dynamics and style transition of a moderate, Vulcanian-driven eruption at Tungurahua (Ecuador) in February 2014: pyroclastic deposits and hazard considerations

Jorge Eduardo Romero1, Guilhem Amin Douillet2, Silvia Vallejo Vargas3, Jorge Bustillos4, Liliana Troncoso4, Juan Díaz Alvarado1, and Patricio Ramón3 Jorge Eduardo Romero et al.
  • 1Departamento de Geología, Universidad de Atacama, Copiapó, Chile
  • 2Earth and Environmental Sciences, Ludwig-Maximilians-Universität, Munich, Germany
  • 3Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador
  • 4Escuela de Geología, Facultad de Geología, Minas, Petróleos y Ambiental (FIGEMPA), Universidad Central del Ecuador, Quito, Ecuador

Abstract. The ongoing eruptive cycle of Tungurahua volcano (Ecuador) since 1999 has been characterised by over 15 paroxysmal phases interrupted by periods of relative calm. Those phases included one Subplinian as well as several Strombolian and Vulcanian eruptions and they generated tephra fallouts, pyroclastic density currents (PDCs) and lava flows. The 1 February 2014 eruption occurred after 75 days of quiescence and only 2 days of pre-eruptive seismic crisis. Two short-lived Vulcanian explosions marked the onset of the paroxysmal phase, characterised by a 13.4 km eruptive column and the trigger of PDCs. After 40 min of paroxysm, the activity evolved into sporadic Strombolian explosions with discrete ash emissions and continued for several weeks.

Both tephra fall and PDCs were studied for their dispersal, sedimentology, volume and eruption source parameters. At large scale, the tephra cloud dispersed toward the SSW. Based on the field data, two dispersal scenarios were developed forming either elliptical isopachs or proximally PDC-influenced isopachs. The minimum bulk tephra volumes are estimated to 4.55 × 106 m3, for an eruption size estimated at volcanic explosivity index (VEI) 2–3. PDCs, although of small volume, descended by nine ravines of the NNW flanks down to the base of the edifice. The 1 February 2014 eruptions show a similar size to the late 1999 and August 2001 events, but with a higher intensity (I 9–10) and shorter duration. The Vulcanian eruptive mechanism is interpreted to be related to a steady magma ascent and the rise in over-pressure in a blocked conduit (plug) and/or a depressurised solidification front. The transition to Strombolian style is well documented from the tephra fall componentry. In any of the interpretative scenarios, the short-lived precursors for such a major event as well as the unusual tephra dispersion pattern urge for renewed hazard considerations at Tungurahua.

Short summary
The 1 February 2014 eruption of the Tungurahua volcano (Ecuador) was the second largest one since the re-awakening in 1999. The eruption showed precursory signs only 48 h before the eruption. The main explosions produced a 13 km eruptive column and pyroclastic density currents that reached the base of the volcano. Here we document the deposits related to the eruption and infer eruption mechanisms and transport processes.