Abstract We conduct analogue experiments using starch and water mixture to understand the key factors controlling morphological transitions from colonnade to entablature of columnar joints. Columnar joints are formed by volume contraction during cooling. The isotherms are assumed to be perpendicular to the direction of the columns. However, observations of the morphological transition between colonnade and entablature and morphology in the entablature part are complex; it is expected that their formations are caused by a change in the distribution of the isotherms. Analogue experiments using starch and water mixtures have been conducted to reproduce the formation of colonnade (straight columns) but not for curved structures. We conduct experiments to reproduce the curved structures and investigate the process of crack propagation from two non-parallel drying surfaces and the relationship between the water distribution and crack development in the starch and water mixture by observing X-ray computed tomography (CT) images over time. In addition, the numbers of columns and cross-sectional areas are measured to interpret the column nucleation, which causes a decrease in the average column width. Based on analytical and numerical solutions of a simple diffusion equation, we examine the effect of critical temperature for crack initiation on curved structures, with a discussion comparing experimental results. The results and discussions suggest that 1) the curvature in crack development is likely controlled not only by the isotherm but also by the temperature at crack initiation and 2) an instantaneous increase in the cooling rate induces the column nucleation at the crack front. Finally, we propose a scenario of morphological transition from colonnade to entablature at Shakushiiwa, Aso-4 welded tuff, in Japan, which shows a threefold structure (upper colonnade – entablature – lower colonnade) based on our experimental results. We introduce two modes of heat transfers: vertical heat transfer Qd within intact rocks by thermal diffusion toward the upper cooling surface and horizontal heat transfer Qv through the cracks. The transition between the modes induces a drastic change in the shape of the isotherm at the crack front, resulting in the morphological transition from colonnade to entablature.

中文翻译：

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柱状节理柱廊向柱状节理形态转变的类比试验

摘要 我们使用淀粉和水的混合物进行模拟实验，以了解控制柱状节理从柱廊到柱状节理形态转变的关键因素。柱状节理是由冷却过程中的体积收缩形成的。假设等温线垂直于柱的方向。然而，观察柱廊和柱状体之间的形态转变以及柱状体部分的形态是复杂的；预计它们的形成是由等温线分布的变化引起的。已经进行了使用淀粉和水混合物的类似实验来重现柱廊（直柱）的形成，但不适用于弯曲结构。我们进行实验以重现弯曲结构，并通过观察 X 射线计算机断层扫描 (CT) 图像来研究两个不平行干燥表面的裂纹扩展过程以及淀粉和水混合物中水分分布与裂纹发展之间的关系。时间。此外，通过测量柱数和横截面积来解释柱形核，这会导致平均柱宽减小。基于简单扩散方程的解析解和数值解，我们研究了临界温度对弯曲结构裂纹萌生的影响，并讨论了比较实验结果。结果和讨论表明：1) 裂纹发展的曲率可能不仅受等温线控制，而且受裂纹萌生温度的控制；2) 冷却速度的瞬时增加导致裂纹前沿处的柱形核形成。最后，我们提出了日本 Aso-4 焊接凝灰岩 Shakushiiwa 从柱廊到柱廊的形态转变方案，该方案根据我们的实验结果显示了三重结构（上柱廊 - 柱廊 - 下柱廊）。我们介绍了两种传热模式：完整岩石内通过向上冷却表面热扩散的垂直传热 Qd 和通过裂缝的水平传热 Qv。模式之间的转变引起裂纹前沿等温线形状的急剧变化，