Global tectonics, eastern Pacific Plate. Satellite-based artwork of an Earth globe showing the tectonic boundaries (yellow lines) in the eastern Pacific Ocean. Seven primary tectonic plates make up the Earth's crust. Phenomena observed at the plate boundaries include earthquakes, volcanic activity, mountain-building, and oceanic trench formation. The particularly active Pacific Plate boundary forms the 'Ring of Fire'. At right are the North American Plate, the South American Plate and the Nazca Plate. The movement of the tectonic plates over the millions of years of geologic time drives the creation, destruction and drifting of the continents. The movement of the tectonic plates is thought to be driven by convection currents in the underlying mantle.