to the southwest; it is an extensive form crossed by many transform faults running perpendicular to its north–south orientation, that is seismically active and susceptible to volcanism. Rift and fault geology The Terceira Rift is a system of fractures that extends from the Mid-Atlantic Ridge to the Glória Fault that represents the main frontier between the Eurasian and African Plates. It is defined by a line of submarine volcanoes and island mounts that extend northwest to southeast for about , from the area west of Graciosa until the islets of the Formigas, that includes the islands of Graciosa, Terceira and São Miguel. Its northwest limit connects to the Mid-Atlantic Ridge, while the southeast section intersects the Gloria Fault southeast of the island of Santa Maria. The Azores Fracture Zone extends from the Glória Fault and encompasses a relatively inactive area to the south of the islands of the Central and Eastern groups north to the Terceira Rift, along a 45° angle. The Glória Fault, for its part, extends along a linear line from the Azores to the Azores–Gibraltar Transform Fault. Volcanoes The island's volcanism is associated with the rifting along the Azores Triple Junction; the spread of the crust along the existing faults and fractures has produced many of the active volcanic and seismic events, while supported by buoyant upwelling in the deeper mantle, some associate with an Azores hotspot. Most of the volcanic activity has centered, primarily, along the Terceira Rift. From the beginning of the island's settlement, around the 15th century, there have been 28 registered volcanic eruptions (15 terrestrial and 13 submarine). The last significant volcanic eruption, the Capelinhos volcano (), occurred off the coast of the island of Faial in 1957; the most recent volcanic activity occurred in the seamounts and submarine volcanoes off the coast of Serreta and in the Pico-São Jorge Channel. The islands have many examples of volcano-built geomorphology including caves and lava tubes (such as the Gruta das Torres, Algar do Carvão, Gruta do Natal, Gruta das Cinco Ribeiras), the coastal lava fields (like the coast of Feteiras, Faial, the Mistério of Prainha or São João on Pico Island) in addition to the inactive cones in central São Miguel Island, the aforementioned Capelinhos on Faial, the volcanic complexes of Terceira or Plinian caldeira of Corvo Island. The islands of the archipelago were formed through volcanic and seismic activity during the Neogene Period;