simple facts
Where is it? Baltica, Guyana [6.4073096658, -58.62373473]
What is in the photo? Three channels converge to form the impressive “Half-and-Half” river
Which satellite took the photo? Landsat 8
When was the photo taken? August 16, 2023
This striking satellite photo shows the contrasting colors of the confluence of Guyana’s three rivers. The colorful waterways are the result of the country’s unique geology as well as increasingly destructive human factors.
This unique hydrology is associated with the Guiana Shield, a 1.7 billion-year-old geological formation that covers Guyana and parts of Venezuela, Brazil, Suriname, and French Guiana. This shield contains a hard, crystalline bedrock made of rocks such as gneiss and granite that is not easily eroded by anything other than running water, which has carved many routes through the region.
In this photo, two small rivers, the Cuyuni River (left) and the Mazaruni River (center left), converge just before joining the Essequibo River (center right) to form one of Guyana’s largest waterways.
The town of Baltica, with a population of about 15,000, is located on land that juts out into the water at the site of the secondary amalgamation. From there, the expanded Essequibo River flows north for approximately 30 miles (50 km) before emptying into the Atlantic Ocean.
Before the merger, the Mazaruni and Essequibo rivers are dark brown, probably due to the effects of tannins (chemicals released by rotting plants). A process similar to brewing tea pollutes waterways.. According to the Earth Observatory, Cuyuni has a light brown color due to high concentrations of suspended sediment in its water.
When rivers converge, light and dark water do not mix easily because changes in sediment levels create differences in density.
The presence of tannins is a natural phenomenon caused by flooding, while the high levels of sediment are the result of mining waste dumped in Mazaruni.
“This image is from a rainy period when all three rivers were swollen and carrying large amounts of sediment.” Evan Detiera hydrologist at Colby College in Maine, told the Earth Observatory. “However, Cuyuni is a clear outlier, and this can be attributed to the intensity of mining upstream.”
Guyana is a mining hotspot primarily due to its vast deposits of gold, diamonds and bauxite, as well as lithium, copper and nickel associated with the Guiana Shield. US Department of Commerce.
Mining in the country began in earnest in the mid-2000s, and since then, the concentration of sediment in the Cuyuni River has probably increased tenfold, Dethier said. Similar changes have been recorded in rivers around the world.
a 2022 survey Dethier and his team found that sediment concentrations in rivers in the Southern Hemisphere have increased by about 40%, largely due to mining and deforestation. However, the opposite is true in the Northern Hemisphere, where the construction of large dams has blocked about half of the flow of sediment.
Changes in global sediment flows may also be affecting the marine environment, the study warns, as the input of sediment in most of the world’s oceans has changed significantly, but it is still too early to know what long-term effects this will have.
Astronaut photos from 2023 showed the Alabama River momentarily transforming into a undulating golden serpent, resembling a Chinese dragon.