Abyssal plains are some of the flattest and smoothest regions on Earth, found at depths between 3,000 and 6,000 meters (9,800 to 19,700 feet) below the ocean surface. They are formed primarily through the processes of sedimentation and tectonic activity.
The formation begins at mid-ocean ridges, where tectonic plates diverge, and magma rises to create new oceanic crust. As this crust moves away from the ridges, it cools and sinks, contributing to the formation of deep ocean basins.
Over time, fine particles and sediments, including clay, silt, and the remains of marine organisms, accumulate on the ocean floor, filling in any irregularities. The continuous process of sedimentation results in the gradual leveling out of the ocean floor. Additionally, volcanic activity and the erosion of underwater features also contribute to the smoothness of abyssal plains.
In essence, the combination of tectonic movements that create oceanic crust, alongside the persistent layering of sediment, results in the development of these expansive, flat sea floors, known as abyssal plains.