Columnar jointing

Fig. 10.9) exhibits columnar jointing up to 1 m from the contact with a sill of the Ferrar Dolerite (50 m) which itself displays columnar jointing. This kind of jointing also occurs in a sandstone bed at the top of the Mackellar Formation (Permian) in theQueen Alexandra Range (Baiett et al. 1986). 

Thin lava flows are broken by joints that may run either at right angles or parallel to the direction of flow. Joints do occur with other orientations but are much less common. Those joints that are normal to the lava surface usually display a polygonal arrangement, but only rarely do they give rise to columnar jointing. These joints develop as the lava cools. First, primary joints form, from which secondary joints arise, and so it continues. 

Typical columnar jointing is developed in thick flows of basalt (Fig. 1.8). The columns in columnar jointing are interrupted by cross joints that may be either flat or saucer-shaped. The latter may be convex up or down. These are not to be confused with platy joints that are developed in lavas as they become more viscous on cooling, so that slight shearing occurs along flow planes. 

Columnar jointing in basalt, Giant s Causeway, Northern Ireland. 

Loess may exhibit sub-vertical columnar jointing. In addition, pipe systems may be developed in loess soils. Extensive pipe systems and sinkholes are present in some loess and have been referred to a loess karst. Pipes tend to develop by weathering and widening that takes place along the joint systems in loess. The depths to which pipes develop may be inhibited by changes in permeability associated with the occurrence of palaeosols. 

Students have seen how an understanding of localised rock mass structures (inclined columnar jointing) can he used to infer broader geological... 

Plate 8 Columnar jointed Basalt and Waterfall (Svartifoss, Iceland) 1996 SvartifossSummer by Andreas Tille. Svartifoss (Black Fall) is a waterfall Vatnajokull National Prack in Iceland. Basalt is the most common igneous rocks. The joint is perpendicular to the surface of the flow and is formed by the cooling of the flow (see Chap. 1)... 

It has also been shown in animal studies that joint deficiencies of iodine and vitamin A result in a significant enlargement of the thyroid which ultimately leads to disordered functions of the gland since vitamin A is required for the normal growth and metabolism of the columnar epithelial cells of the thyroid. 

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