What is the main cause of oceanic trench formation?

Oceanic trench formation is primarily caused by the subduction of tectonic plates. This process occurs when one tectonic plate, usually an oceanic plate, is forced beneath another plate, which can be either oceanic or continental. As the subducting plate sinks into the Earth's mantle, it leads to the creation of deep, narrow trenches in the ocean floor, which are among the deepest parts of the ocean.

The immense pressure and heat generated during this subduction process not only create these structures but also contribute to geological activity, such as volcanic eruptions and earthquakes along subduction zones. This relationship between plate tectonics and the oceanic trenches highlights the dynamic nature of the Earth's crust and the significance of tectonic processes in shaping underwater geological features.

In contrast to the other choices: river erosion primarily affects land formations and does not lead to the creation of oceanic trenches; meteor impacts do not consistently lead to the formation of trenches but can create craters; and glacial activity influences coastal landforms and can reshape continental areas rather than the deep-sea trenches associated with plate tectonics. Therefore, subduction remains the primary and most relevant cause for the development of oceanic trenches.