Publication Date:
2020-01-08
Description:
For an improvement in the quality of conduit flow and dome-related explosive eruption models, knowledge of the
preeruption or precollapse density of the rocks involved is necessary. As close investigation is impossible during eruption, the
best substitute comes from quantitative investigation of the eruption deposits. The porosity of volcanic rocks is of primary
importance for the eruptive behaviour and, accordingly, a key-parameter for realistic models of dome stability and conduit flow.
Fortunately, this physical property may be accurately determined via density measurements.
We developed a robust, battery-powered device for rapid and reliable density measurements of dry rock samples in the
field. The density of the samples (sealed in plastic bags at 250 mbar) is determined using the Archimedean principle. We
have tested the device on the deposits of the 1990–1995 eruption of Unzen volcano, Japan. Short setup and operation
times allow up to 60 measurements per day under fieldwork conditions. The rapid accumulation of correspondingly large
data sets has allowed us to acquire the first statistically significant data set of clast density distribution in block-and-ash
flow deposits.
More than 1100 samples with a total weight of 2.2 tons were measured. The data set demonstrates that the deposits of the last
eruptive episode at Unzen display a bimodal density distribution, with peaks at 2.0F0.1 and 2.3F0.1 g/cm3, corresponding to
open porosity values of 20 and 8 vol.%, respectively. We use this data set to link the results of laboratory-based fragmentation
experiments to field studies at recently active lava domes.
Description:
Published
Description:
65-75
Description:
partially_open
Keywords:
field-based density measurements
;
dome
;
Unzen volcano
;
explosive eruption
;
block-and-ash flow
;
fragmentation behaviour
;
volcanology
;
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
710471 bytes
Format:
application/pdf
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