1:45 PM - 3:15 PM
[O07-P03] Observation of Columnar Joints and Research on its Origin
Keywords:Columnar Joints, Izu Peninsula
It is widely known that hexagonal columnar joints is more than others. From our previous studies which use data from the Izu Peninsula and overseas columnar joints, it is known that ‘The complicated shapes of columnar joints mean the magma solidified quickly, and the more simple the shapes are, the slower the magma sets’. There is a positive correlation between the rapidity of magma’s solidification and the complexity of columnar joints’ shapes.
We conducted an analysis which investigated discovers this relationship in terms of circularity. Using the standard deviation of circularity and the kurtosis of heptagonal number distribution, we made one graph of columnar joints and distinguished it into three areas: upper left, lower left, and lower right. In this graph, the vertical axis is ‘deviation of circularity’ and the horizontal axis is ‘kurtosis of heptagonal number distribution’.The upper left’s rock was made in a thin dyke and the cooling was heterogeneous. As for the lower right, the magma was solidified underground, and the other’s magma was so thick that it set slowly. This magma’s cooling was homogeneneous under natural conditions. This history and the feature of this graph are similar, so according to this graph and circumstances, the kurtosis of circularity decreases, as the homogeneity of cooling magma increases and vice versa.
We pictured the procedure of forming starch columnar joints every three minutes. We finally found that cracks occur from one point and continuously, and columnar joints which stick to the container were larger than those which lie in the center. From this observation, we established a hypothesis that natural columnar joints which were made of magma adjacent to rock are relatively larger.
We once tried to make rock columnar joints, using an electric furnace(AS ONE HTR-1010). This purpose was to make the model of occuring columnar joints. As a result, there were quenching edges on the surface and irregular joints inside, however we weren’t able to make ‘columnar’ joints. We believe this was because the time of cooling was very short and that the experiment was small, compared to natural formations.
We conducted an analysis which investigated discovers this relationship in terms of circularity. Using the standard deviation of circularity and the kurtosis of heptagonal number distribution, we made one graph of columnar joints and distinguished it into three areas: upper left, lower left, and lower right. In this graph, the vertical axis is ‘deviation of circularity’ and the horizontal axis is ‘kurtosis of heptagonal number distribution’.The upper left’s rock was made in a thin dyke and the cooling was heterogeneous. As for the lower right, the magma was solidified underground, and the other’s magma was so thick that it set slowly. This magma’s cooling was homogeneneous under natural conditions. This history and the feature of this graph are similar, so according to this graph and circumstances, the kurtosis of circularity decreases, as the homogeneity of cooling magma increases and vice versa.
We pictured the procedure of forming starch columnar joints every three minutes. We finally found that cracks occur from one point and continuously, and columnar joints which stick to the container were larger than those which lie in the center. From this observation, we established a hypothesis that natural columnar joints which were made of magma adjacent to rock are relatively larger.
We once tried to make rock columnar joints, using an electric furnace(AS ONE HTR-1010). This purpose was to make the model of occuring columnar joints. As a result, there were quenching edges on the surface and irregular joints inside, however we weren’t able to make ‘columnar’ joints. We believe this was because the time of cooling was very short and that the experiment was small, compared to natural formations.