“A Mountain in the Sea” is the widely used slogan for Corsica, the large Mediterranean Island off of France and Italy. A more geologically accurate version might read: “Two Mountain Ranges in the Sea.” A line that runs roughly from L‘Île Rousse on the north coast, through Corte in the interior, to Favone on the southeast coast, divides Corsica into two distinct geologic terranes.

Most of the rock to the west of the line is granite, a type of igneous rock. The mountains and hills on the west side of the line are roots of an ancient range that rose between 345 and 225 million years ago during the Hercynian orogeny (mountain-building period).

Everything to the east of the line is “Alpine Corsica.” The rocks on this part of the island were crumpled into mountains hundreds of millions of years later, when the African and Eurasian plates collided to form the Alps. The layered rocks on this side of the island are mainly schist, limestone, and other sedimentary rocks that formed on the seafloor.

These two periods of mountain-building, plus millions of years of rainfall and erosion carving the highlands, sculpted the rugged terrain that defines Corsica today. The tallest peak, Monte Cinto, rises 2,706 meters (8,878 feet) above sea level. Corsica is home to 19 other mountains higher than 2,000 meters, mainly on the western side of the island.

On May 17, 2017, the Operational Land Imager (OLI) on Landsat 8 captured this image of Corsica. In addition to all of the mountains, a few plains, lagoons, estuaries, and deltas ring the coast, particularly the eastern coast.