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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Bubble plumes generated during recharge of basaltic magma reservoirs
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Bubble plumes generated during recharge of basaltic magma reservoirs

机译：玄武岩浆储层补给过程中产生的气泡羽

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摘要

CO_2 is relatively insoluble in basaltic magma at low crustal pressures. It therefore exists as a gas phase in the form of bubbles in shallow crustal reservoirs. Over time these bubbles may separate gravitationally from the magma in the chamber. As a result, any new magma which recharges the chamber from deeper in the crust may be more bubble-rich and hence of lower density than the magma in the chamber. Using scaling arguments, we show that for typical recharge fluxes, such a source of low-viscosity, bubble-rich basalt may generate a turbulent bubble plume within the chamber. We also show that the bubbles are typically sufficiently small to have a low Reynolds number and to remain in the flow. We then present a series of analogue laboratory experiments which identify that the motion of such as turbulent bubble-driven line plume is well described by the classical theory of buoyant plumes. Using the classical plume theory we then examine the effect of the return flow associated with such bubble plumes on the mixing and redistribution of bubbles within the chamber. Using this model, we show that a relatively deep bubbly layer of magma may form below a thin foam layer at the roof. If, as an eruption proceeds, there is a continuing influx at the base of the chamber, then our model suggests that the bubble content of the bubbly layer may gradually increase. This may lead to a transition from lava flow activity to more explosive fire-fountaining activity. The foam layer at the top of the chamber may provide a flux for the continual outgassing from the flanks of the volcano [Ryan, Am. Geophys. Union Geophys. Monogr. 91 (1990)] and if it deepens sufficiently it may contribute to the eruptive activity [Vergniolle and Jaupart, J. Geophys. Res. 95 (1990) 2793-3001].
机译：在低地壳压力下，CO_2相对不溶于玄武岩浆。因此，它以气相形式以气泡形式存在于浅层地壳储层中。随着时间的流逝，这些气泡可能在重力作用下与室内的岩浆分离。结果，比腔室中的岩浆更深地填充壳的任何新的岩浆可能更富含气泡，因此密度更低。使用比例论证，我们表明，对于典型的补给通量，这种低粘度，富含气泡的玄武岩源可能会在室内产生湍流的气泡羽流。我们还表明，气泡通常足够小以具有低的雷诺数并保留在流中。然后，我们提出了一系列模拟实验室实验，这些实验确定了经典的浮力羽流理论很好地描述了诸如湍流气泡驱动的线羽流的运动。然后，使用经典羽流理论，我们研究了与此类气泡羽流相关的回流对室内气泡混合和重新分布的影响。使用该模型，我们表明岩浆的相对较深的气泡层可能在屋顶的薄泡沫层下方形成。如果随着喷发的进行，腔室底部不断涌入，则我们的模型表明气泡层的气泡含量可能会逐渐增加。这可能导致从熔岩流活动过渡到更具爆炸性的灭火活动。腔室顶部的泡沫层可提供助焊剂，以使火山的侧面不断脱气[Ryan，Am。地理学。联合地球物理。 Monogr。 91（1990）]，如果深度足够深，则可能有助于爆发活动[Vergniolle and Jaupart，J. Geophys。 Res。 95（1990）2793-3001]。

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