What geological process causes the mid-oceanic ridge to form?

The formation of mid-oceanic ridges is primarily attributed to the activity of plate tectonics, specifically the process of tectonic plates pulling apart, also known as divergent plate boundaries. As these plates separate, magma from the mantle rises to fill the gap, leading to the creation of new oceanic crust. This volcanic activity is a part of the process but is a result of the tectonic plates being pulled apart rather than the initiating factor. The continuous movement of these plates not only creates the ridge itself but also facilitates the ongoing volcanic activity that forms new geological features.

In this context, while volcanic activity can be associated with mid-ocean ridges, it is not the fundamental cause of their formation; rather, it is a consequence of the tectonic movements that create the ridges. Other options, such as coral reef accretion and earthquake activity, do relate to geological processes but do not play a pivotal role in the formation of mid-ocean ridges specifically.