Fractured

The rocks at the Tessellated Pavement are Permian ( Malbina Formation) with beds which vary in thickness and composition ( some are mudstones, some are sandstones, all are poorly sorted and pebbly, and were formed during the Permian glacial period). The deposits have been compacted and deeply buried and are, only now, being exposed to erosion. The modern pavements at about mean sea level, reflect the erosion which has taken place since sea levels stabilised about 6,000 years ago. The cliffs have retreated since that time and continue to collapse in an irregular, fairly unpredictable way.
These rocks have been compacted and loaded by up to 3 km of other rocks since their formation. They were also deposited across an old escarpment formed along the early north-south boundary of a granite intrusion. The variations in thickness of the sequence and its compaction have produced a rock mass which has been pre-stressed with a variation in load stresses from west to east.When the load is released, by uplift and erosion, it tends to break north-south preferentially.
Also, the rocks, as they are exposed are attacked by the elements and the presence of salt is a key factor. Chemical processes may change the composition and lead to expansion of the rock, and it cracks. These minor cracks tend to have preferred orientations determined by the pre-stressing, or they trend toward those preferred orientations. Also, as the salt crystals form in each tidal cycle as the water on the surface evaporates, they expand and stress the rock surface.. The pores are enlarged and the rock is slowly blown apart, grain by grain.
The incipient joints link and grow with time and, if the beds are nearly horizontal and of the right composition and thickness, yield a regular pattern ultimately determined by the pre-stressing factors. The joints tend to straighten as they are widened by weathering and the patterns grow downward from the surface demonstrating their weathering-stress release origin. Patterns vary from bed to bed since bed properties are crucial. The complete combination of characters is rare and hence "tessellated" patterns are not common.
Nikon D700, Nikkor 17-35 mm @ 17 mm,
8.0 s @ f/18, ISO 100,
Singh Ray GND's

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