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The fragmentation of highly viscous magma by rapid decompression is a young\ntechnique. For the first time an experimental tool permits the analysis of the influence\nof pressure, temperature and texture on the fragmentation of magma. The physical\nrange of the experiments is close to the natural conditions of dome collapse.\nThe experiments were performed at temperatures up to 950\xb0C. The initial pressure\ndifference in the range of 10 to 250bar is in good agreement to the natural conditions.\nIn addition to the analysis of the fragmentation threshold, the rapid decompression\nexperiments permit analysis of the primary particle distribution above the\nfragmentation level of an eruption. Further analyses were aimed at the influence of\ncrystals on the particle distribution.\nAn experimental set-up was used to investigate the speed of the propagating\nfragmentation wave, initiated by the rapid decompression of porous magma samples.\nThe fragmentation speed experiments were performed at ~20\xb0C using two dynamic\npressure transducers. A new technique was designed to extend the temperature\nrange of the fragmentation speed experiments up to 950\xb0C.\nNext to the fragmentation experiments a comparison of analytical methods for the\ncharacterisation of the experimental pyroclasts was necessary. The applicability of\nthe characterisation method to both experimental and fieldwork was of major interest.\nThe experiments were performed on Dacite samples form Mt. St. Helens\n(Washington, USA), Fugendake (Unzen volcano complex, Japan) and basaltic\nAndesites of the 1994 eruption of Merapi (Java, Indonesia).\nThe experimental investigation, the methodological and technical development are\nscope of the presented dissertation.