In early November, 2012, thick tan sediment discolored the Guadalquivir River and spilled into the Golfo de Cádiz (Gulf of Cádiz) along Spain’s southwestern coast. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this true-color image on November 12.
The sediment plume pours from the river in to the Gulf, and forms a convoluted semi-circle, illustrating the complicated currents which washed that area of the Gulf on that day. Because the river is tan, most of the sediment likely comes from the river itself, washed from rains along the shores upstream, or high volume flows in the river. However, the Guadalquivir River prodelta – the submerged portion of the delta that lies beyond the delta front – is rich in fine-grained mud. High flow from the river into the prodelta can raise the mud from the bottom, increasing the turbidity in the Gulf.
The sediments from the Guadalquivir River have attracted ongoing attention from scientists, and not just when they are visible in satellite images. On April 25, 1998, a tailings dam for a pyrite mine burst along the Guadiamar River, a tributary of the Guadalquivir. The accident released 4 million cubic meters of acidic water and 2 million cubic meters of mud, which spread downstream. Threats to water quality and wildlife health have therefore been an ongoing area of research.