Publication Date:
2017-04-03
Description:
Rapid mass movements of rock fragments are among the most hazardous natural phenomena.
The ability to foresee their mobility is important when assessing natural hazards in
volcanic regions. The dynamics of granular flows is however a challenging multivariate
problem. Among the variables that affect their mobility we can include grain size and
flow volume. Unfortunately, there are no generally accepted scaling laws describing these
phenomena with the certainty to have taken into consideration all important aspects of
nature. There are also different ways to assess mobility. Some authors, for example,
adopt the distance travelled by the flow front or other arbitrary distances which are
inappropriate for energy budget considerations because these flows deform during motion
and deposition. Because of the difficulties inherent in direct field observations of
these catastrophic events, we resort to laboratory experiments where granular material is
released down a chute whose shape is similar to the profile of Mayon Volcano in the
Philippines. Our experiments show that in flows of angular rock fragments, the smaller
the grain size (all the other things equal), the larger is mobility. Importantly, this mobility is
assessed measuring the distance travelled by centres of mass. Particle image
velocimetry analysis of high speed video camera images shows also that the smaller the
grain size, the smaller is the agitation of the fragments. This can explain the increase
of runout distance as grain size decreases because fragments that are less agitated
dissipate less energy. This should also explain why larger flow volumes are known to
be more mobile. The larger the volume, the relatively smaller is the mass of a
fragment with respect to the total mass of the flow so that fragments of larger flows are
less agitated and for this reason dissipate less energy.
Description:
Published
Description:
Tenerife, Spain
Description:
3.6. Fisica del vulcanismo
Description:
open
Keywords:
pyroclastic flows
;
mobility
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Poster session
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