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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Painéis ► em encontros internacionais

 

Referência Bibliográfica


KUEPPERS, U., DINGWELL, D.B. (2006) - The ejection speed of experimental pyroclasts. AGU Fall Metting, San Francisco, USA, 11 - 15 de Dezembro (Poster).

Resumo


The multiparametric monitoring of active volcanoes in unrest relies on an ever increasing repertoire of physico- chemical methods. Nevertheless, abrupt changes in the eruptive behaviour of explosive volcanoes is one of the greatest challenges to effective early warning One of the most deadly can be a vulcanian explosive generating significant volcanic hazard and risk from ballistic projectiles. These often come with little warning. Here, in order to investigate the relationship between explosion characteristics and the kinetics of pyroclast ejection, we performed a series of rapid decompression experiments at well-constrained and reproducible physical conditions. To do this, we adapted the low-pressure section of the "fragmentation bomb" and suited it with two pairs of a laser beam source and a receptor arranged horizontally in the path of the vertically ejected pyroclasts. From the known distance (0.76 and 1.76 m above the original sample surface) of the laser beams and the time delay between the pressure decay and the partial shadowing of the two laser beams, we calculated the ejection speed of the experimental pyroclasts. To the best of our knowledge, this is first experimental quantification of the ejection speed of pyroclasts from rapidly decompressed magma. The evaluated ejection speed values are in the range of up to 100s of meters per second. They reveal a clear influence of the physical properties of the samples and the applied pressure. The transfer of potential fragmentation energy into ejection velocity is being analysed. The ejection speed (together with the ejection angle) has a major influence on the potentially hazardous area around a volcano. In combination with systematic seismic monitoring and interpretation, these results may one day become the basis for a tool to determine the pressurisation state of a volcano in quasi-real-time using ballistic data.

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