Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK.
Department of Earth- and Environmental Science, Ludwig-Maximilians-Universitat, Theresienstr. 41, 80333, Munich, Germany.
Nat Commun. 2018 Nov 8;9(1):4696. doi: 10.1038/s41467-018-07187-w.
Magma is a viscoelastic fluid that can support fracture propagation when local shear stresses are high, or relax and flow when shear stresses are low. Here we present experiments to confirm this using synthetic and natural magmatic liquids across eruptive conditions and use Maxwell's linear viscoelasticity to parameterize our results and predict the maximum stresses that can be supported during flow. This model proves universal across a large range of liquid compositions, temperatures, crystallinity and rates of strain relevant to shallow crustal magma ascent. Our results predict that the 2008 Volcán Chaitén eruption resided in the viscous field at the onset of magma ascent, but transitioned to a mixed viscous-brittle regime during degassing, coincident with the observed combined effusive-explosive behaviour during dome extrusion. Taking a realistic maximum effusive ascent rate, we propose that silicic eruptions on Earth may straddle the viscous-to-brittle transition by the time they reach the surface.
岩浆是一种黏弹性流体，当局部剪切应力较高时，可以支持断裂扩展，当剪切应力较低时可以松弛和流动。在这里，我们通过使用合成和天然岩浆液体在喷发条件下进行实验来证实这一点，并使用麦克斯韦线性黏弹性来参数化我们的结果并预测在流动过程中可以承受的最大应力。该模型在与浅层地壳岩浆上升相关的大范围液体组成、温度、结晶度和应变率下具有通用性。我们的结果预测，2008 年柴坦火山喷发在岩浆上升开始时处于粘性场，但在脱气过程中过渡到粘性-脆性混合状态，与观察到的穹顶挤压过程中同时存在的爆发性喷发行为一致。考虑到实际的最大喷发上升速度，我们提出地球上火山喷发可能在到达地表之前就跨越了黏性到脆性的转变。
