Reference Work Entry

Beaches and Coastal Geology

Part of the series Encyclopedia of Earth Science pp 48-49


  • Robert T. Siegfried

Aquafacts are wave-faceted rocks found on beaches. Although their occurrences are not rare, little attention has been given them. The characteristics of the features are similar to those of ventifacts, which owe their origin to wind action and abrasion (Keunen, 1947).

The requirements for the formation of aquafacts include: a sand supply sufficient to cause abrasion (pebbles tend to destroy the faceted surface); a boulder that is firmly wedged in place, a small projection of a rocky subsurface, or, most commonly, a rock large enough not to be moved by wave action.

Abrasion occurs on the seaward side of the rock. Sand-sized particles, brought up the beach by swash action, strike the rock, gradually producing the smooth, faceted surface. Backwash is not strong enough to cause abrasion on the leeward side. As the facet is cut into the original surface, a distinct ridge, perpendicular to the onrushing swash, is produced across the crest of the rock.

Aquafacts are not likely to fo ...

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