Wet Tafoni

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Wet Tafoni
Wet Tafoni

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Just south of Pescadero, CA, is a small beach locally known as Pebble Beach. Instead of sand it is covered with pebbles that have eroded out of poorly consolidated marine terrace sedimentary deposits in the face of the short bluff at the top of the beach. The rocks that surround and underlie the pebbles are sedimentary rocks. Many of them have this wonderful pattern on them.

This is a weathering pattern known as tafoni. It is likely caused by repeated soaking of porous rock during which small amounts of the rock material dissolves and migrate in solution to the surface of the rock. This results in a gradual weakening of the inner portions of the rock's structure.

Then, as water evaporates from the surface of the rock the dissolved materials remineralize, creating a harder crust-like surface. Eventually that outer crust remains as the inner structure weathers, then erodes away leaving the tafoni structure.

If the new cavities are oriented properly they can capture pebbles that then rattle around in the cavity as waves pass, causing the cavities to grow. But many of these tafoni pockets are not oriented in a direction that would capture pebbles, so that process would not fully explain the pattern.

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Taken on: June 5, 2016
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Camera: Nikon D200, f/4.0, 1/500 sec, 50mm (=75mm), ISO 100 (more info) (hide info)
Camera: Nikon D200
Lens: AF Nikkor 50mm f/1.4D
Aperture: f/4.0
Exposure Time: 0.002 sec (1/500)
Focal Length: 50mm (35mm equivalent: 75mm)
ISO: 100
Exposure Bias: -1/3 EV
Flash: No Flash
Exposure Program: Manual
Exposure Mode: Manual
Metering Mode: Spot
White Balance: Manual
Light Source: Fine Weather
Saturation: High
Sharpness: Hard
Color Space: sRGB
Software: Ver.2.01
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