Abstract The thermal properties of volcanic rocks are crucial to accurately model heat transfer in volcanoes and in geothermal systems located within volcanic deposits. Here we provide laboratory measurements of thermal conductivity and thermal diffusivity for variably porous andesites from Mt. Ruapehu (New Zealand) and variably altered basaltic-andesites from Merapi volcano (Indonesia) measured at ambient laboratory pressure and temperature using the transient hot-strip method. The specific heat capacity of each sample was then calculated using these measured values and the bulk sample density. Thermal conductivity and thermal diffusivity decrease as a function of increasing porosity, but specific heat capacity does not vary systematically with porosity. For a given porosity, saturation with water increases thermal conductivity and specific heat capacity, but decreases thermal diffusivity. Measurements on samples from Merapi volcano show that, compared to the unaltered samples from Mt. Ruapehu, hydrothermal alteration deceases thermal conductivity and thermal diffusivity, and increases specific heat capacity. We use an effective medium approach to parameterise these data, showing that when the porosity and pore-fluid properties are scaled for, the measured values agree well with theoretical predictions. We find that despite the microstructural complexity of the studied andesites, porosity is the principal parameter dictating their thermal properties. To understand whether the measured changes in thermal properties are sufficient to influence natural processes, we model heat transfer from magma to the surrounding host-rock by solving Fick's second law cast in 1D Cartesian (dyke geometry) and cylindrical (conduit geometry) coordinates. We provide models for different host-rock porosities (0–0.6), different initial magmatic temperatures (800–1200 °C), and different levels of host-rock alteration. Our modelling shows how the cooling of a dyke and conduit is slowed by a higher host-rock porosity and by increased hydrothermal alteration. The thermal properties provided herein can help improve modelling designed to inform on volcanic and geothermal processes.

中文翻译：

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多孔安山岩的热学性质

摘要 火山岩的热特性对于准确模拟火山和位于火山沉积物中的地热系统的热传递至关重要。在这里，我们提供了来自 Mt. 的可变多孔安山岩的热导率和热扩散率的实验室测量结果。Ruapehu（新西兰）和来自默拉皮火山（印度尼西亚）的变质玄武安山岩在实验室环境压力和温度下使用瞬态热带法测量。然后使用这些测量值和整体样品密度计算每个样品的比热容。热导率和热扩散率随着孔隙率的增加而降低，但比热容不会随孔隙率系统地变化。对于给定的孔隙率，与水饱和会增加热导率和比热容，但会降低热扩散率。对默拉皮火山样本的测量表明，与来自 Mt. 的未改变样本相比。Ruapehu，热液蚀变会降低热导率和热扩散率，并增加比热容。我们使用有效的介质方法来参数化这些数据，表明当孔隙度和孔隙流体特性按比例缩放时，测量值与理论预测非常吻合。我们发现，尽管所研究的安山岩的微观结构很复杂，但孔隙度是决定其热性能的主要参数。要了解测得的热特性变化是否足以影响自然过程，我们通过求解一维笛卡尔（堤坝几何）和圆柱（管道几何）坐标中的 Fick 第二定律来模拟从岩浆到周围主岩的热传递。我们提供了不同主岩孔隙度 (0-0.6)、不同初始岩浆温度 (800-1200 °C) 和不同程度的主岩蚀变的模型。我们的模型显示了更高的主岩孔隙度和增加的热液蚀变如何减缓堤坝和管道的冷却。此处提供的热特性有助于改进旨在为火山和地热过程提供信息的建模。以及不同程度的母岩蚀变。我们的模型显示了更高的主岩孔隙度和增加的热液蚀变如何减缓堤坝和管道的冷却。此处提供的热特性有助于改进旨在为火山和地热过程提供信息的建模。以及不同程度的母岩蚀变。我们的模型显示了更高的主岩孔隙度和增加的热液蚀变如何减缓堤坝和管道的冷却。此处提供的热特性有助于改进旨在为火山和地热过程提供信息的建模。