MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY MICHAEL SZOENYI / SCIENCE PHOTO LIBRARY
Eroded sandstone. This is part of Uluru (Ayers Rock), in Australia's Northern Territory. The type of erosion that has taken place here, tafoni (or cavernous) erosion, takes place where there are high temperature and humidity differences. It is a combination of physical and chemical weathering processes, and starts when water brings dissolved minerals to the rock surface. When the water dries, the minerals form crystals that force small particles to flake off the rock. Eventually, large cavities such as these form, having a cavernous and honeycombed shape because the surface layer of rock is harder than the interior.
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