Sunday 23 October 2016
Thursday 13 October 2016
Hoodoos and ironstone rocks - Writing on Stone Provincial Park, AB
A hoodoo is a rock formation which is caused by differential resistance to erosion. This means that some parts of the hoodoo are harder than others and these hard parts last longer. In the hoodoos below, the tops are the hardest part and they protect the soft rock below from wearing away.
The hoodoos in the Milk River valley are made of sandstone which is sand-sized particles cemented together by calcite, silica, or an iron oxide. Some sandstone is quite hard, but sandstone can be so soft that it brushes away when you touch it.
Ironstones are reddish-brown rocks that are very hard. When the sand was being deposited on the ancient beach, living organisms became trapped in the sand. This organic material slowly attracts molecules of iron mineral around it. Slowly, over millions and millions of years, layer upon layer of iron, an ironstone concretion is formed. Ironstones are so hard that when they are exposed on a hoodoo, the soft sandstone around them is eroded away and the ironstone falls out, leaving a hole. The holes in the hoodoos can result in very exotic and curious forms.
Source:http://www.uleth.ca/vft/milkriver/hoodoos.html
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