The world’s widest river

“The misnamed Rio Plata (silver river) occupies what was once a broad river valley that was drowned by rising seas during the melting at the end of the last ice age. The Spanish colonists hoped to find another Potosi inland, and gave it its name in the hope that tonnes more silver would flow down it to enrich Spain. It is about 290Km long, and starts at the confluence of the Rio Parana/Paraguay delta (that flows over Iguazu falls many miles to the north) and the Rio Uruguay. Its funnel starts two Km wide, opening out to about 220 at the Atlantic coast, making it the world’s widest river (some dispute this, considering it a marine gulf). It now forms the border between Argentina and Uruguay, flowing above the Precambrian Rio de la Plata craton, and was the site of a major naval encounter in the last world war.

The drainage basin that feeds it is the second largest on the continent, after the Amazon, covering about a quarter of the landmass, starting far to the north in southern Brazil and Paraguay. The sediments on both sides of the river are very different. In Montevideo one has lush golden sandy beaches, at Buenos Aires and its delta suburb of Tigre lush treescapes growing in fine dark mud. This is due to the sediment loads of the different rivers as they pass over different lithologies on their meandering journeys, picking up different types of rock particle along the way. The Parana, in the upper left of the image carries muddy silt, and the Uruguay to the right fine sands. A submerged shoal divides it into freshwater and estuarine brackish water. ”


Image credit of the river at sunset: Karen Nyberg.

via [The Earth Story]

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