In “jökulhlaups”, that are common in the Skeiðará glacial river, large icebergs are brought down on the sandur plain. Some of these get stuck there and root deeply into the sand. Gradually they melt down and deep holes or depressions form into which material accumulates from the surrounding. These circular depressions are referred to as ice kettles. Some times a layer of sand covers the surface of these depressions but underneath water, mud or ice may still be present. Accidents have happened and men riding on horses are known to have sunk into such holes and drowned.
In the big 1996 jökulhlaup from Skeiðará river a large number of icebergs were broken up from Skeiðarárjökull and laid to rest on Skeiðarársandur. Once there they began to melt down during the following summer. Such icebergs tend to be deeply rooted and may last for many years in the sand, sometimes not visible because a blanket of sand covers the depression surface.
The aerial photograph below, that was taken on August 29th, 1988, a multitude of ice kettles can be seen in the area south of the where the Skeiðará river comes from beneath the glacier.