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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Rheological control on the radiant density of active lava flows and domes
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Rheological control on the radiant density of active lava flows and domes

机译：活性熔岩流和穹顶辐射密度的流变控制

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During an effusive-extrusive eruption, the capability of an active lava body (flow or dome) to radiate thermal energy depends on how the lava discharge rate is accommodated by the expansion of the magma body and by the cooling of its surface. This feature can be described by a single empirical parameter, defined "radiant density" (crad; in J m~(-3)) that, for a given discharge rate, expresses the efficiency of the lava body to change its area and/or to insulate its inner core, thus modulating the heat radiated from the active surface. By comparing the Volcanic Radiative Energy (VRE; in J), detected by MODIS during 28 eruptions at 18 active volcanoes, with their erupted lava volumes (Vol; in m~3), we show that the radiant density (c_(rad)=VRE/Vol) is inversely proportional to the silica content of the erupted lava. Basic lavas (45-52 wt.% SiO_2) have the highest observed radiant density (1 to 4 × 10~8 J m~(-3)) while intermediate (52-63 wt.% SiO_2) and acidic (>63 wt.% SiO2) lavas show a gradually lower radiant densities (1.5 to 9 × 10~7 J m~(-3) and 0.2 to 1 × 10~7 J m~(-3) for intermediate and acidic composition, respectively). We regard this correlation as the result of the control that the rheology of lavas exerts on cooling and spreading processes of related bodies. In particular, we found that for any given compositional group the radiant density is essentially related to a "characteristic thickness" of active lavas, at the time of a satellite acquisition. We suggest that the radiant density of effusive/extrusive lava bodies can be predicted (± 50%) by means of an empirical relationship based on the SiO_2 content of the erupted lava. This makes this parameter very useful in observing volcanic activity, especially in remote regions where access may not be possible. By measuring the energy radiated during an eruption and by assuming a lava composition (based on the tectonic setting or magmatic province), we suggest that the radiant density can be used to estimate lava discharge rates and erupted volumes for volcanoes characterised by effusive or extrusive activity.
机译：在喷发性喷发期间，活跃的熔岩体（流动或穹顶）辐射热能的能力取决于熔岩体的膨胀和其表面的冷却如何适应熔岩的排放速率。这个特征可以用一个单一的经验参数来描述，定义为“辐射密度”（crad；在J m〜（-3）中），对于给定的排放速率，该参数表示熔岩体改变其面积和/或效率的效率。使其内芯绝缘，从而调节从活动表面辐射的热量。通过比较MODIS在18个活火山的28次喷发期间检测到的火山辐射能（VRE; in J）与火山喷发量（Vol; in m〜3），我们得出辐射密度（c_（rad）= VRE / Vol）与喷出的熔岩的二氧化硅含量成反比。碱性熔岩（45-52 wt。％SiO_2）具有最高的观测辐射密度（1至4×10〜8 J m〜（-3）），而中间熔岩（52-63 wt。％SiO_2）和酸性（> 63 wt％ ％的SiO2）熔岩显示出逐渐降低的辐射密度（中间和酸性成分分别为1.5至9×10〜7J m〜（-3）和0.2至1×10〜7Jm〜（-3）。我们认为这种相关性是控制熔岩流变作用于相关物体的冷却和扩散过程的结果。尤其是，我们发现，对于任何给定的成分组，在获取卫星时，辐射密度与活性熔岩的“特征厚度”基本相关。我们建议可以通过基于喷发熔岩的SiO_2含量的经验关系来预测喷出/喷出熔岩体的辐射密度（±50％）。这使该参数在观察火山活动时非常有用，尤其是在无法访问的偏远地区。通过测量喷发过程中辐射的能量并假设熔岩成分（基于构造背景或岩浆区），我们建议辐射密度可用于估计火山喷发率和火山喷发量，这些火山的特征是喷发或挤压活动。

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