Island-encapsulating eolian sedimentary systems of the Canary and Cape Verde archipelagos

Abstract

Eolian dunes are generally absent or poorly developed on oceanic islands. Yet, large-scale eolian 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, eolian transport corridors, and downwind sediment depocenters, each of which is characterized 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 characterized 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 headlandbypass dunes and longshore transport in the littoral zone in the intervening embayments. Depocenters comprise extensive eolian 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 semiarid environments with unidirectional or strongly asymmetrical transport-capable winds (i. e., trade winds).