The viscosity of volcanic melts is a dominant factor in controlling the fluid dynamics of magmas and thereby eruption style. It can vary by several orders of magnitude, depending on temperature, chemical composition and water content. The experimentally accessible temperature range is restricted by melt crystallisation and gas exsolution. Therefore, modelling viscosity as a function of temperature and water content is central to physical volcanology. We present a model that describes these dependencies by combining a physically motivated equation for temperature dependence of viscosity and a glass transition temperature () model for the effects of water. The equation uses the viscosity at infinite temperature , and the steepness factor as fitting parameters. We investigate the effect of leaving free as a fitting parameter and fixing its value, by fitting anhydrous viscosity data of 45 volcanic melts using the temperature dependent model. Both approaches describe experimental data well. Using a constant therefore provides a viable route for extrapolating viscosity from data restricted to small temperature intervals. Our model describes hydrous data over a wide compositional range of terrestrial magmas (26 data sets) with comparable or better quality than literature fits. With constrained, we apply our model to viscosities derived by differential scanning calorimetry and find – by comparing to viscometry based data and models – that this approach can be used to reliably describe the dependence of viscosity on temperature and water content. This introduces important implications for modelling the effects of nanostructure formation on viscosity.

中文翻译：

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模拟无水和含水火山熔体的粘度

火山熔体的粘度是控制岩浆流体动力学和喷发方式的主要因素。它可以有几个数量级的变化，具体取决于温度、化学成分和水含量。实验上可达到的温度范围受熔体结晶和气体析出的限制。因此，将粘度建模为温度和水含量的函数是物理火山学的核心。我们提出了一个模型，该模型通过结合用于粘度的温度依赖性的物理驱动方程和用于水影响的玻璃化转变温度 ( ) 模型来描述这些依赖性。的等式使用在无限温度下的粘度，和陡度因子作为拟合参数。我们通过使用温度相关模型拟合 45 种火山熔体的无水粘度数据，研究将free 作为拟合参数并固定其值的影响。这两种方法都很好地描述了实验数据。因此，使用常数提供了一种可行的途径，用于从仅限于小温度间隔的数据外推粘度。我们的模型描述了广泛组成范围的陆地岩浆（26 个数据集）的含水数据，其质量与文献拟合相当或更好。和受约束，我们将我们的模型应用于差示扫描量热法得出的粘度，并通过与基于粘度测定法的数据和模型进行比较，发现这种方法可用于可靠地描述粘度对温度和水含量的依赖性。这对模拟纳米结构形成对粘度的影响具有重要意义。