Experimental Rheology of Magmatic Emulsions and Foams: Effects of Composition, Temperature, Shear Rate and Bubble Content

含泡岩浆的流变性既有基本原因，也有实际原因。因为气泡是可变形的，所以气泡的形状在流动过程中会发生变化，这就产生了乳状液(熔体+蒸汽)的剪切速率相关的粘度。在低剪切速率下，气泡保持以表面张力为主的球形，乳液粘度与无气泡熔体粘度之比随着气泡含量的增加而增大。在高剪切速率下，情况正好相反；随着气泡含量的增加，乳液相对于熔体的粘度降低。因为少量的挥发性成分，如H2O和CO2在岩浆中普遍存在，而且这些化合物很少能溶解，所以几乎所有的岩浆在低压和喷发时都会变得挥发饱和(因此是气泡的)。使用专门为此而制造的高扭矩精密同心圆筒粘度计对岩浆乳状液和泡沫的流变性随温度、剪切速率、气泡含量和熔体组成的函数进行量化，将提供有关气泡形成的岩浆的流变性的基本信息。这些流变学数据将通过发展可用于物理火山学模型研究的本构关系来总结，并将填补我们对岩浆粘性性质知识的重要空白。

9972922SperaThe rheological properties of bubble-bearing magmas are of interest for fundamental as well as practical reasons. Because bubbles are deformable, bubble shapes change during flow and this gives rise to a shear-rate dependent viscosity for the emulsion (melt + vapor). At low shear rate, bubbles retain a surface tension -dominated spherical shape and the ratio of the emulsion viscosity to the bubble-free melt viscosity increases as the bubble content increases. At high rates of shear just the opposite occurs; the viscosity of the emulsion decreases relative to the melt as the bubble content increases. Because small amounts of volatile components such as H2O and CO2 are ubiquitous in magmas and because these compounds are sparingly soluble, virtually all magmas become volatile-saturated (hence bubbly) at low pressure and upon eruption. Quantification of the rheological properties of magma emulsions and froths as a function of temperature, shear rate, bubble-content and melt composition using a high torque precision concentric cylinder viscometer specifically fabricated for this purpose will provide basic information concerning the rheological properties of bubble-beraing magmas. These rheological data will be summarized by developing constitutive relations that can be used in physical volcanological modelling studies and will fillan important gap in our knowledge regarding the viscometric properties of magma.