The anatomy of a pyroclastic density current: the 10 July 2015 event at Volcan de Colima (Mexico)
Por:
Capra, L., Sulpizio, R., Marquez-Ramirez, V. H., Coviello, V., Doronzo, D. M., Arambula-Mendoza, R., Cruz, S.
Publicada:
1 abr 2018
Categoría:
Geochemistry and petrology
Resumen:
Pyroclastic density currents (PDCs) represent one of the most dangerous
phenomena occurring in explosive volcanic eruptions, and any advance in
the physical understanding of their transport and sedimentation
processes can contribute to improving their hazard assessment. The 10-11
July 2015 eruption at Volcan de Colima provided a unique opportunity to
better understand the internal behaviour of PDCs based on seismic
monitoring data. On 10 July 2015, the summit dome collapsed, producing
concentrated PDCs that filled the main channel of the Montegrande
ravine. A lahar monitoring station installed 6 km from the volcano
summit recorded a PDC before being completely destroyed. Real-time data
acquisition from a camcorder and a geophone that were part of the
station, along with field observations and grain-size data of the
pyroclastic deposits, are used here to interpret the internal flow
structure and time-variant transport dynamics of low-volume,
valley-confined concentrated PDCs. The PDC that reached the monitoring
station moved at a velocity of similar to 7 m/s and filled a 12-m-deep
channel. The outcrops show massive, block-and-ash flow deposits with
trains of coarse clasts in the middle and towards the top of the
depositional units. The seismic record gathered with the geophone was
analysed for the time window when the flow travelled past the sensor.
The geophone record was also compared with the recordings of a broadband
seismic station located nearby. Two main frequency ranges were
recognised which could be correlated with the basal frictional forces
exerted by the flow on the channel bed (10-20 Hz) and a collisional
regime (20-40 Hz) interpreted to be associated with a clast segregation
process (i.e. kinematic squeezing). This latter regime promoted the
upward migration of large blocks, which subsequently deviated towards
the margin of the flow where they interacted with the sidewall of the
main channel. The energy calculated for both seismic components shows
that the collisional regime represents 30% of the total energy
including an important sidewall-stress component. These results,
gathered directly from a moving flow, contribute to unravelling the
internal behaviour of concentrated PDCs providing information on energy
partitioning and particle-particle interactions. This confirms previous
assumptions inferred from field observations, and tested by analogue or
numerical modelling. The nature of the contact between grains is still
poorly documented in natural PDCs, and there is still much uncertainty
and discussion about dominant forces in such currents. Data reported
here may thus be useful to better constrain the physics of low-volume,
valley-confined concentrated PDCs and our findings need to be considered
in theoretical models. In parallel, this study shows how geophones can
provide a cheap alternative for PDC detection.
Filiaciones:
Capra, L.:
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro 76230, Mexico
Sulpizio, R.:
Dipartimento di Scienze della Terra e Geoambientali, via Orabona 4, Bari, Italy
IDPA-CNR, via Mario Bianco 9, Milan, Italy
Dipartimento Sci Terra & Geoambientali, Via Orabona 4, I-70125 Bari, Italy
CNR, IDPA, Via Mario Bianco 9, Milan, Italy
Marquez-Ramirez, V. H.:
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro 76230, Mexico
Coviello, V.:
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro 76230, Mexico
Doronzo, D. M.:
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico
Institute of Earth Sciences Jaume Almera, ICTJA, CSIC, Group of Volcanology, SIMGEO UB-CSIC, Lluis Sole i Sabaris s/n, Barcelona, Spain
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro 76230, Mexico
Inst Earth Sci Jaume Almera, CSIC, ICTJA, Grp Volcanol,SIMGEO UB, Lluis Sole & Sabaris S-N, Barcelona 08028, Spain
Arambula-Mendoza, R.:
Centro Universitario de Estudios e Investigaciones en Vulcanología (CUEIV), Universidad de Colima, Colima, Mexico
Univ Colima, CUEIV, Colima, Mexico
Cruz, S.:
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, Mexico
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro 76230, Mexico
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