Pyroclastic currents and deposits: state of the art and perspectives

 

Lecturer:

Dr. Domenico d'Oronzo, ICTJA-CSIC

Date:

Apr, 21, 2017 12:00 am

Venue:

Sala d'Actes del Institut de Ciències de la Terra Jaume Almera (ICTJA-CSIC)

Location:

C/ Solé i Sabarís s/n, Barcelona

Further information

Dr. Adelina Geyer

 

Abstract

Pyroclastic currents are gravity flows that vary between two end members, concentrated and dilute. They are the most hazardous events of explosive volcanism, particularly due to transformations of one end member into the other. When a pyroclastic current interacts with complex topographies or inhabited areas, the flow velocity and density can strongly change at its base, and this in turns affects both the pyroclastic deposits and the flow behaviour and impact. Here, a step-by-step integrated approach, from numerical to experimental through field observations, is presented to assess what happens during these interactions.

(1) 3D Eulerian-Lagrangian numerical simulations of volcanic column collapse (Vulcanian and Plinian) were performed at the scale of tens of meters. The simulations solved for the associated flow velocity and density, hence for the dynamic pressure (one of the impact parameters of pyroclastic currents);

(2) large-scale experiments of the simulated events were carried out, and the dynamic pressure was measured in order to validate the numerical model. The modelled pressures agree with the experimental ones, and both agree with values calculated from the experimental pyroclastic deposits;

(3) the simulations were extended to a natural case-study, the Island of Vulcano in Italy, in order to reproduce the 3D interactions between small-to-intermediate volume pyroclastic currents and the actual topography. The dynamic pressures agree with the ones extracted from the deposits at Vulcano;

(4) 2D simulations over simpler morphologies showed that massive deposits can form from a velocity- and density-stratified pyroclastic current against hills and inside valleys, whereas finely laminated deposits can form after flow-topography interaction, and this agrees with the field evidences at Vulcano;

(5) flow-morphology interactions were zoomed in the scale of buildings showing that vertical dynamic pressures also exist in the interaction zone, in agreement with other geophysical flows like dust shear flows and hurricanes in the environment.
Main reference for this contribution on pyroclastic currents is the following review paper:

R, S., D. P, D. D.M, and S. D (2014), Pyroclastic density currents: state of the art and perspectives, Journal of Volcanology and Geothermal Research, 283, 36-65, doi: http://dx.doi.org/10.1016/j.jvolgeores.2014.06.014.

 

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