BEADED STREAM, MACKENZIE DELTA, CANADA :: Sometimes in the summer months, small pools occur at the polygon`s corners of the patterned permafrost ground. These little lakes could become up to 3 m deep and 30 m in diameter. Driven by gravity, water flows along the polygon`s rims from one pool to the other, so that the pools get connected by a stream. Scientists call it beaded drainage. This phenomenon is typical for thawing permafrost.