Publication Date:
2017-04-04
Description:
To visualize the behavior of erupting magma in volcanic conduits, we performed shock tube experiments on the ductile–brittle
response of a viscoelastic medium to diffusion-driven bubble expansion. A sample of shear-thinning magma analogue is saturated by
gas Ar under high pressure. On rapid decompression, Ar supersaturation causes bubbles to nucleate, grow, and coalesce in the sample,
forcing it to expand, flow, and fracture. Experimental variables include saturation pressure and duration, and shape and lubrication of
the flow path. Bubble growth in the experiments controls both flow and fracturing, and is consistent with physical models of magma
vesiculation. Two types of fractures are observed: i) sharp fractures along the uppermost rim of the sample, and ii) fractures pervasively
diffused throughout the sample. Rim fractures open when shear stress accumulates and strain rate is highest at the margin of the flow (a
process already inferred from observations and models to occur in magma). Pervasive fractures originate when wall-friction retards
expansion of the sample, causing pressure to build-up in the bubbles. When bubble pressure overcomes wall-friction and the tensile
strength of the porous sample, fractures open with a range of morphologies. Both types of fracture open normally to flow direction, and
both may heal as the flow proceeds. These experiments also illustrate how the development of pervasive fractures allows exsolving gas
to escape from the sample before the generation of a permeable network via other processes, e.g., bubble coalescence. This is an
observation that potentially impact the degassing of magma and the transition between explosive and effusive eruptions.
Description:
Published
Description:
771-785
Description:
JCR Journal
Description:
reserved
Keywords:
volcanic conduit
;
analogue experiment
;
vesiculation
;
fragmentation
;
degassing
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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