How the Delta Formed

The modern Mississippi River Delta formed over the last 7,000 years in a dynamic process known as the delta cycle. Each delta cycle results in a new delta lobe, created over a period of around 1,000-2,000 years as the river carries sediments from the interior of the continent and deposits them near its mouth in the warm waters of the Gulf of Mexico. When enough sediment stacks up underwater, plants begin to grow, and even more sediment and organic materials accumulate as plant communities thrive and develop.

As the delta lobe continues to build, the river's path to the Gulf becomes longer and more difficult. In response, the river finally changes course, abandoning the older lobe and cutting a shorter route to the Gulf, starting the process again.

Coastal Louisiana's historic delta lobes

These abandoned lobes gradually sink and erode, forming extremely productive estuaries and leaving barrier island arcs behind to mark their former extent. New lobes form with the river's new route, building up new land for marsh plants and trees to take hold. This constant ebb and flow creates a dynamic and ever-changing mosaic of habitats and natural resources. A natural delta exists in a state of constant change.

By the time of European settlement, the Mississippi River Delta Plain stretched across a remarkable 7,000 square miles, making it one of the largest river deltas in the world. At this time, the river was active in the Balize delta lobe, an area now often called the birdsfoot delta. Because the end of this lobe lies near the continental shelf and thus deep water, it provided tremendous opportunities for waterborne commerce and transportation, leading to the rise of New Orleans and other port cities and trade routes.

Satellite view of the Mississippi River Delta (NASA)

But by the 20th century, the birdsfoot had grown old for a delta lobe, and the Mississippi River had begun taking a more direct path to the sea. By the mid-20th century, scientists and engineers knew that the Atchafalaya River, a distributary more than 100 miles west of the birdsfoot, was capturing more and more of the river's flow. If the river were allowed to change course as it naturally would, the ports of Baton Rouge and New Orleans would be cut off. To combat this, the U.S. Army Corps of Engineers installed a series of large water control structures — the Old River Control Structure complex — to freeze time and keep the river from changing course.

Today, the delta’s natural cycles of change and rebirth have been ground almost to a halt by human activities, laying the groundwork for today's ecological collapse. Read more about what went wrong.