Which geological feature is formed as a result of subduction?

Subduction occurs when one tectonic plate moves underneath another and sinks into the mantle due to gravity. This geological process often results in the formation of deep ocean trenches. The Mariana Trench is the most well-known example of such a trench, located in the western Pacific Ocean. It represents the deepest part of the world's oceans and is formed specifically at the convergent boundary where an oceanic plate is subducting beneath another oceanic plate.

In contrast, the Great Barrier Reef is a coral reef system built by coral polyps, which is not related to subduction. The Appalachian Mountains were formed mainly by ancient tectonic events that involved the collision and folding of continental plates, not subduction. The Sahara Desert, being a vast arid region, is shaped by climate and sedimentary processes, rather than tectonic activities like subduction. Thus, the Mariana Trench is the geological feature directly associated with the subduction process.