NASA Satellite Image Reveals How a Meandering River Shaped Congaree's Ancient Forest

A new satellite image from NASA's Earth Observatory shows how the meandering Congaree River has shaped Congaree National Park in South Carolina, where about 80% of the park lies within the river's floodplain. The image, captured by the Operational Land Imager (OLI) on the Landsat 9 satellite, shows curving bands of green tracing old channels, ridges and swales left behind as the river gradually shifted across the flat, low-lying terrain.

On flat terrain, water flows faster on the outside of a river bend, eroding the outer bank, while it flows slower on the inside, depositing sediment to build sandy features called point bars. Over time this process can cut off a bend from the main channel, forming U-shaped oxbow lakes. The park's Weston Lake, about 1.2 miles (1.9 kilometers) from the visitor center, is one of its most permanent oxbow lakes, while Bates Old River, roughly 4 miles long, is one of the longest oxbow lakes in South Carolina. As abandoned channels and oxbow lakes slowly fill with sediment, some become shallow wetlands called sloughs, where flood-tolerant cypress-tupelo forests grow.

The Congaree River overflows its banks several times a year, mostly in winter and early spring but also after summer and fall hurricanes, spreading nutrient-rich silt across the floodplain that helps nourish the forest's unusually large trees. Loggers targeted the area's forests in the 1880s, but frequent flooding, muddy roads and mosquitoes meant most of the floodplain forest escaped the widespread logging that transformed other parts of the southeastern United States.

By the 1950s, conservationists had recognized how rare old-growth forests of this type had become in the region. Congress designated the area a national monument in 1976, and it became a national park in 2003. Congaree trees such as the possumhaw, water hickory, loblolly pine, laurel oak, swamp tupelo and sweetgum have at times held national or state size records for their species.