Exploring separated gas-magma flows in basaltic volcanoes using analogue experiments at a range of scales
Abstract
The decoupling of magmatic gas from magma during transport to the surface may result in cyclical and unsteady flow of magma within basaltic conduits. These flows are characterized by low-intensity, impulsive explosions which may recur rhythmically for long periods of time. We present the results of scaled analogue experiments which elucidate the separated flow processes which underpin such eruptions. Experiments are conducted in liquid-filled vertical pipes ranging from 0.02 to 0.2 m in diameter, and 2 to 12 m in height, allowing us to investigate Reynolds numbers 10-3 < Re < 105, encompassing the natural range for volcanoes. The chief novelty of this study is that we explore the role played by the boundary conditions at the top and at the bottom of the pipe: i) the top of the conduit is either plugged, rheologically impeded, or open; ii) the base of the conduit is either closed (zero flux) or held at constant pressure. This latter condition mimics the presence of a magma chamber at the lower end of the conduit. Our study combines the direct observation of in-conduit fluid dynamic processes with measured pressure variations inside and outside the pipe. Our results illustrate that changing boundary conditions dramatically affects the degree of overpressure acquired by the decoupled gas phase during ascent and, consequently, the explosivity of the eruption. We place our results in the context of field observations and data from Stromboli, and discuss the insights afforded by our experiments into the shallow expansion/explosion dynamics and the interpretation of seismo-acoustic signals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V14A..07D
- Keywords:
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- 8414 VOLCANOLOGY / Eruption mechanisms and flow emplacement;
- 8445 VOLCANOLOGY / Experimental volcanism