Lava domes form when highly viscous magmas erupt on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma. Here, we develop a 2-D axisymmetric model of magma extrusion on the surface and lava dome evolution and analyse the dome morphology using a finite-volume method implemented in Ansys Fluent software. The magma/lava viscosity depends on the volume fraction of crystals and temperature. We show that the morphology of domes is influenced by two parameters: the characteristic time of crystal content growth (CCGT) and the discharge rate (DR). At smaller values of the CCGTs, that is, at rapid lava crystallization, obelisk-shaped structures develop at low DRs and pancake-shaped structures at high DRs; at longer CCGTs, lava domes feature lobe- to pancake-shaped structures. A thick carapace of about 70 per cent crystal content evolves at smaller CCGTs. We demonstrate that cooling does not play the essential role during a lava dome emplacement, because the thermal thickness of the evolving carapace remains small in comparison with the dome's height. A transition from the endogenic to exogenic regime of the lava dome growth occurs after a rapid increase in the DR. A strain-rate-dependent lava viscosity leads to a more confined dome, but the influence of this viscosity on the dome morphology is not well pronounced. The model results can be used in assessments of the rates of magma extrusion, the lava viscosity and the morphology of active lava domes..

中文翻译：

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数值模拟推断的熔岩穹顶形态

当高粘性岩浆在表面喷发时，形成熔岩穹顶。根据岩浆的流速和流变学，可以区分几种类型的熔岩穹顶形态。在这里，我们开发了岩浆挤压在表面和熔岩穹顶演化的二维轴对称模型，并使用在Ansys Fluent软件中实现的有限体积方法分析了穹顶形态。岩浆/熔岩的粘度取决于晶体的体积分数和温度。我们表明圆顶的形态受两个参数的影响：晶体含量增长的特征时间（CCGT）和放电速率（DR）。当CCGTs值较小时，即熔岩快速结晶，在低DRs下形成方尖碑形结构，在高DRs下形成薄饼形结构。在较长的CCGT中，熔岩穹顶具有叶状至薄饼状的结构。较小的CCGT会演化出约70％晶体含量的厚甲壳。我们证明，在熔岩穹顶安置期间，冷却作用并不重要，因为与穹顶的高度相比，不断发展的甲壳的热厚度仍然很小。熔岩穹顶生长从内源性向外源性转变的过程是在DR迅速增加后发生的。应变率相关的熔岩粘度导致穹顶更加封闭，但是这种粘度对穹顶形态的影响并不十分明显。该模型结果可用于评估岩浆挤出速率，熔岩粘度和活性熔岩穹顶的形态。因为进化的甲壳的热厚度与圆顶的高度相比仍然很小。熔岩穹顶生长从内源性向外源性转变的过程是在DR迅速增加后发生的。应变率相关的熔岩粘度导致穹顶更加狭窄，但是这种粘度对穹顶形态的影响并不十分明显。该模型结果可用于评估岩浆挤出速率，熔岩粘度和活性熔岩穹顶的形态。因为进化的甲壳的热厚度与圆顶的高度相比仍然很小。熔岩穹顶生长从内源性向外源性转变的过程是在DR迅速增加后发生的。应变率相关的熔岩粘度导致穹顶更加封闭，但是这种粘度对穹顶形态的影响并不十分明显。该模型结果可用于评估岩浆挤出速率，熔岩粘度和活性熔岩穹顶的形态。但是这种粘度对圆顶形貌的影响并不十分明显。该模型结果可用于评估岩浆挤出速率，熔岩粘度和活性熔岩穹顶的形态。但是这种粘度对圆顶形貌的影响并不十分明显。该模型结果可用于评估岩浆挤出速率，熔岩粘度和活性熔岩穹顶的形态。