The breakup of Pangea began with the formation of the Tethys Sea during the Triassic and continued with the opening of the Atlantic during the Jurassic. The latter began about 150 million years ago and continues today, pushing the North and South American Plates to the west. The Caribbean Plate, once part of the Pacific, wedged between the two American Plates as they moved westward and began to override them.
Along the eastern edge of the Caribbean Plate, the American Plates are subducting; as these plate margins are forced downward toward the Earth's mantle, they begin to melt, producing volcanism to the west of the subduction zone. This has led to a volcanic island arc (part of the Lesser Antilles), from the Virgin Islands on the north to Grenada on the south; today, 17 active volcanoes dot this island chain. Mt. Pelee, on Martinique, erupted in 1902, killing more than 30,000 people; most recently, the Soufriere Hills Volcano, on Montserrat, has been erupting intermittently since 1995, devastating much of the island and forcing most of its population to leave.
At the west edge of the Caribbean Plate, which includes the Central American countries south of Mexico, the Cocos Plate, a remnant of the Farallon Oceanic Plate, is subducting beneath the west edge of El Salvador, Honduras and Guatemala, producing the volcanic chain that runs along the Pacific coast of Central America. More isolated areas of subduction have occurred along the northern and southern edges of the Caribbean Plate as the American Plates have scraped past; this is especially evident off the north coast of South American, were other islands represent periods of volcanism.
