The Azores are entirely of volcanic origin. They have been created by outpourings of lava from the ocean floor.
The high level of activity in the area is a result of three major tectonic plates meeting here. The North American Plate to the northwest of the Azores is gradually drifting west, the Euroasian Plate to the northeast is drifting east and south and finally the African Plate is drifting east and north. The small Azores Microplate, which is drifting westwards, further complicates the picture. Where the plates pull apart (diverge) lava outpourings have created mid-oceanic ridges, the highest parts of these rise out of the sea to create volcanic islands. The mid-Atlantic ridge on which the Azores lie extends for 16,000 km. and islands along its length include Iceland.
The oldest of the islands, Santa Maria, was formed some 7 million years ago and then sank and reappeared. As a result it is the only island to have appreciable marine fossils in its rocks. The youngest island is Pico. it was mainly formed some 300 thousand years ago. There was an even younger island - Sabrina - not far off from Sao Miguel that appeared in 1811 and was claimed by the British but sadly it vanished under the oceans just a few months later.