A group of islands on the floodplain of the Okavango alluvial fan were studied to establish the processes which lead to the initiation and growth of islands. It was found that islands are initiated by the mound-building activities of the termite Macrotermis michaelseni. Shrubs and trees are able to colonize these mounds, which result in increased transpiration. As a result, precipitation of calcite and silica from the shallow ground water occurs preferentially beneath the mounds, resulting in vertical and especially lateral growth, causing island expansion.