How are abyssal hills formed by volcanism and block faulting?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

Abyssal hills are small, topographically distinct features found on the ocean floor, primarily formed through the interplay of volcanism and block faulting.1

The formation process typically occurs at spreading centres:

Volcanism: In the neovolcanic zone at the crest of a spreading centre, episodic volcanic activity initiates the construction of discrete volcanic hills.1
Block Faulting: As the oceanic crust moves away from the ridge, it undergoes tectonic modification. The zone of active faulting further shapes these features or creates them through the fracturing and displacement of the crustal blocks.1

The relative influence of these processes is often dictated by the spreading rate. At slower spreading rates, block faulting becomes the dominant factor, resulting in hills with greater relief. These hills are essentially the sediment-covered equivalents of the basaltic prominences found on the upper flanks of oceanic ridges, and they are believed to underlie the majority of the world's ocean floor.1