CONSTRAINING VOLCANIC ERUPTION DYNAMICS BY MAGMA FRAGMENTATION EXPERIMENTS

Driven by the rising importance of hazard and risk management that demands reliable and quantitative predictions of volcanic processes, the investigation of volcanic eruptions is becoming systematic, quantitative and rigorous. The scientific study of volcanic phenomena cannot rely solely on field data, as direct observations of eruption processes in the field are limited by the very nature of the events. Thus innovative laboratory experiments play an increasingly important role in volcano research, to explore novel phenomena and to perform systematic investigations of volcanic processes.

Magma fragmentation is one of the key processes of explosive volcanism, and can be studied by laboratory experiments using varying analogue materials and natural magma.

We have performed rapid decompression experiments on a broad range of natural magmas. The experiments were carried out with a shock-tube like apparatus (20-900°C, 0.1-40 MPa) designed by Alidibirov and Dingwell (1996) and subsequently modified to tackle a variety of open questions (e.g. Scheu et al. 2008). We could determine the threshold pressure required to achieve fragmentation as inversely proportional to the pore fraction (Spieler, et al., 2004). Further we gained information on the speed of fragmentation (Scheu, et al., 2006), the permeability of eruptive products (Mueller, et al., 2005), and the influence of permeability on fragmentation (Mueller et al. 2008) as well as the efficiency of fragmentation (Kueppers, et al., 2006). Recently a transparent autoclave and ejection chamber enabled us to monitor the fragmentation process and particle ejection with high-speed videos (Alatorre et al. 2011).

This enhanced understanding of the mechanisms of magmatic fragmentation and their underlying physics allow insights into processes during explosive volcanism and their characteristic size distribution of the ejected tephra.