Publication Date:
2023-01-16
Description:
The distribution of clasts deposited around a volcano
during an explosive eruption typically contoured by
isopleth maps provides important insights into the associated
plume height, wind speed and eruptive style. Nonetheless,
a wide range of strategies exists to determine the largest
clasts, which can lead to very different results with obvious
implications for the characterization of eruptive behaviour
of active volcanoes. The IAVCEI Commission on Tephra
Hazard Modelling has carried out a dedicated exercise to
assess the influence of various strategies on the determination
of the largest clasts. Suggestions on the selection of
sampling area, collection strategy, choice of clast typologies
and clast characterization (i.e. axis measurement and
averaging technique) are given, mostly based on a thorough
investigation of two outcrops of a Plinian tephra deposit from
Cotopaxi volcano (Ecuador) located at different distances
from the vent. These include: (1) sampling on a flat paleotopography
far from significant slopes to minimize remobilization
effects; (2) sampling on specified-horizontal-area sections
(with the statistically representative sampling area depending
on the outcrop grain size and lithic content); (3) clast characterization
based on the geometric mean of its three orthogonal
axes with the approximation of the minimum ellipsoid (lithic
fragments are better than pumice clasts when present); and
(4) use of the method of the 50th percentile of a sample of 20
clasts as the best way to assess the largest clasts. It is also
suggested that all data collected for the construction of
isopleth maps be made available to the community through
the use of a standardized data collection template, to assess the
applicability of the new proposed strategy on a large number
of deposits and to build a large dataset for the future development
and refinement of dispersal models.
Description:
Published
Description:
680
Description:
3V. Dinamiche e scenari eruttivi
Description:
JCR Journal
Description:
restricted
Keywords:
tephra deposit
;
field strategies
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
