Physical Feature: Spur and groove reefs

Gledstanes shipwreck at Kure Atoll hidden in a spur-and-groove reef. Photo Credit: Tane Casserly

One of the effects of large waves on reefs is the formation of spur-and-groove topography. On windward facing reefs, where most of the large waves impact, deep furrows are carved into the reef. These furrows, or grooves, provide channels for water and sediment to be carried off the reef after the large waves impact. This topography is similar to the channels carved by rivers that etch valleys, but is more uniform. On some of the northern atolls the depth of these grooves can approach twenty feet, appearing like underwater slot canyons. Large predators use these unique formations for hunting and ambushing of prey, and maritime archaeologists have found long lost shiprwreck artifacts hidden in these underwater canyons.

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