Abanico del Pilcomayo y Estero Patiño

The Pilcomayo rises in the Bolivian Andes and runs about 1,100 km to the Paraguay River. In the Chaco it loses gradient, overflows and drops so much fine sand that it shifts course again and again, a process geologists call avulsion. According to an academic study, over the centuries this built South America’s largest functioning alluvial fan, about 210,000 km², with many abandoned channels, and the river is one of the most sediment-laden on Earth, at about 140 million tonnes a year (figures from that source).

Estero Patiño, a wetland of about 1,500 km² on the Pilcomayo’s course in Presidente Hayes, vanished in the early 21st century because of the river’s sedimentation and course change, which gave rise to the La Estrella wetland in Argentina.