Reference work entry
The gas in a volcanic lava flow will diffuse upwards while flowing and leave holes in the lava after cooling; this is called a vesicular structure. Its shape can be round, elliptical, cloud-shaped, or tube-shaped. The shape of the hole and the array orientation usually indicates the lava flow direction. Vesicular structures are common in China’s geoparks that are composed of basalt (Fig. 4).
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