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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Magma fragmentation speed: an experimental determination
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Magma fragmentation speed: an experimental determination

机译：岩浆破碎速度：实验确定

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The propagation speed of a fragmentation front, combined with the ascent velocity of magma is, in all likelihood, a controlling factor in the dynamics of explosive volcanic eruptions. Direct measurement of the 'fragmentation speed' in natural systems appears to be impossible at present. Fortunately, laboratory experiments can provide information on the propagation speed of the fragmentation front. Here we present the results of fragmentation speed determinations using a so-called 'fragmentation bomb'. These are, to the best of our knowledge, the first in situ fragmentation speed determinations performed on magma. Natural magma samples (Merapi basaltic andesite, Mount St. Helens dacite and Unzen dacite) have been investigated in the temperature range of 20-950℃ and at pressures up to 25 MPa. Two techniques have been employed. Firstly, in experiments at 20℃, dynamic pressure transducers were placed above and below the magma samples and the fragmentation speed of the magma sample was derived from an analysis of the decompression curves. Secondly, at elevated temperatures, an alternative technique was introduced and successfully employed. This involved the severing via fragmentation of conducting wires placed within the samples at various heights. Fragmentation speeds are very low, falling in the range of 2-70 m/s and increasing with an increase in the magnitude of the decompression step responsible for the fragmentation. The first high-temperature determination seems consistent with low-temperature results. Implications for explosive volcanism are discussed briefly.
机译：碎片锋面的传播速度，加上岩浆的上升速度，很可能是爆炸性火山爆发动力学的控制因素。目前似乎无法直接测量自然系统中的“碎片速度”。幸运的是，实验室实验可以提供有关碎片前沿传播速度的信息。在这里，我们介绍使用所谓的“碎片炸弹”确定碎片速度的结果。据我们所知，这是在岩浆上进行的第一个原位破碎速度测定。天然岩浆样品（Merapi玄武岩安山岩，圣海伦斯山辉晶岩和Unzen辉晶岩）已在20-950℃的温度范围内和最高25 MPa的压力下进行了研究。已经采用了两种技术。首先，在20℃的实验中，动压传感器分别置于岩浆样品的上方和下方，并通过对减压曲线的分析得出岩浆样品的破碎速度。其次，在升高的温度下，一种替代技术被引入并成功采用。这涉及通过以不同高度放置在样品内的导线的断裂来切断。碎裂速度非常低，落在2-70 m / s的范围内，并且随着负责碎裂的减压步骤大小的增加而增加。第一次高温测定似乎与低温结果一致。简要讨论了爆炸性火山作用的含义。

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