They're called 'braided river' systems, as they often resemble an intricate jumble of patterns, intertwining in an almost inexplicable fashion. These networks of river channels flow from the glaciers toward the sea, carrying vital nutrients for the ecosystem along the way, in the form of sediment. When the flow of the rivers decreases, the sediment gets deposited on the river bed, leaving behind small temporary islands of dark volcanic sand that cause the channels of the rivers to split.