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How do abyssal plains form on the deep ocean floor?

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Map graphic showing the boundaries of the five oceans-Pacific, Atlantic, Indian, Arctic, and Southern-using color-coded regions. Four different map projections are included: North Pole view, South Pole view, International Date Line view, and Greenwich Meridian view, each displaying the oceans' extents around the continents. — ocean Earth's oceans and their marginal seas cover nearly 71 percent of the planet's surface.

Abyssal plains are vast, flat regions of the deep ocean floor that form through the accumulation of land-derived sediment in abyssal depressions. This process effectively smooths out preexisting irregular or hilly topography, resulting in surfaces that vary only slightly in depth over large distances.1

The primary mechanism for this sediment transport is the turbidity current—a dense, sediment-laden slurry triggered by the slumping of coarse material from continental slopes. As these currents flow down the slopes due to gravity, they deposit layers of sand, silt, and gravel across the abyssal floor. These deposits, known as turbidites, are often interbedded with fine-grained clay and the microscopic remains of marine organisms that settle slowly through the water column between turbidity-current events.12

In some areas, incomplete burial of the original seafloor may leave isolated volcanic hills rising above the otherwise flat plain. These plains are most common in the Atlantic Ocean, where they can extend from the base of a continent to the Mid-Atlantic Ridge.12