These hoodoos are formed in banks of fluvio-glacial alluvium that was deposited on mountainsides during the last glaciations in the Alps. As this glacial clay was eroded by rain and snow melt over thousands of years some rocks protected the clays beneath them. There are two main hypotheses as to why the clay beneath the cap rock becomes harder and more resistant but the outcome is that the loose surrounding clays are washed away and the columns erode at a much slower rate. When the cap rock eventually slips off, the column becomes pointed as the top erodes faster. The formations change at quite quickly and this column has eroded to a thin wall with pinnacles. Photographed in Theus, Alpes-Haute Provence, France.