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A window above us.
An arch forms when the elements carve out a hole – known as a “window” – into a rock formation. It usually begins when water seeps into small crevices in the stone. When trapped water freezes, it expands, widening the crevice. This allows more water to settle in these openings and for wind to assault more of the stone’s surface.
In JTNP they began forming between 135-155 million years ago when magma pushed up into the overlying rock then cooled and hardened. Since then, the overlying rock has eroded away, exposing the granite. Once above ground, rain and wind eroded a hole within the rock slab while rounding its top, resulting in an arch.
Just consider that Arches’ formations are carved out of soft sandstone while those at Joshua Tree were whittled out of hard granite. It’s a testament to Mother Nature’s patience…wind, rain, and the freeze-thaw cycle always win out.
An arch forms when the elements carve out a hole – known as a “window” – into a rock formation. It usually begins when water seeps into small crevices in the stone. When trapped water freezes, it expands, widening the crevice. This allows more water to settle in these openings and for wind to assault more of the stone’s surface.
In JTNP they began forming between 135-155 million years ago when magma pushed up into the overlying rock then cooled and hardened. Since then, the overlying rock has eroded away, exposing the granite. Once above ground, rain and wind eroded a hole within the rock slab while rounding its top, resulting in an arch.
Just consider that Arches’ formations are carved out of soft sandstone while those at Joshua Tree were whittled out of hard granite. It’s a testament to Mother Nature’s patience…wind, rain, and the freeze-thaw cycle always win out.