Island-encapsulating aeolian sedimentary systems of the Canary and Cape Verde Archipelagos

Aeolian dunes are generally absent or poorly developed on oceanic islands. Yet, large-scale aeolian sedimentary systems characterize the oceanic islands of the Canary and Cape Verde archipelagos. These island-encapsulating sedimentary systems extend around or across entire islands and comprise upwind source areas, aeolian transport corridors and downwind sediment depocentres, each of which is characterised by distinctive dune forms. Upwind beaches are denuded of sand, while downwind locations exhibit progressive shoreline accretion. Cross-island transport corridors developed in topographic lows on the island surface are characterised by a variety of landforms including sandsheets, barchanoid dunes and transverse dunefields, depending on topography and local sediment volume and supply. Circum-island transport corridors develop when the island topography is high and sediment transport takes place on the island margins, alternating between headland-bypass dunes and longshore transport in the littoral zone in the intervening embayments. Depocentres comprise extensive aeolian dunefields, prograding beaches or beach ridges depending on local topography. Recognition of the interconnected nature of the components of these contemporary systems has important management implications.The presence of these sedimentary systems in the Canary and Cape Verde chains can be attributed to a particular combination of geological and geographical factors. The thick lithosphere in which the island chains occur slows subsidence rates and creates long-lived oceanic islands that are exposed to weathering and erosion for several million years during which terrestrial denudation and biogenic sediment production creates a sufficient volume of littoral sediment. From a geographical perspective, these islands are in arid or semi-arid environments with unidirectional or strongly asymmetrical transport-capable winds (i.e. Trade Winds).