Some sources suggest that an eruption in the 3rd century BC separated Therasía from the northwest of Thera. Strabo vividly describes (Geography, I, 57) another eruption in probably 197–96 BC, in which the island, then called Hiera and now known as Palaia Kameni, first appeared from under the sea as ‘flames burst out from the sea for a period of four days, causing the water to seethe and flare up' as the island slowly emerged. In 46 AD, another islet, Thia, appeared and vanished (Pliny). 726 AD, saw another violent eruption, creating the northeastern lobe of Palaia Kameni. In 1570 a part of the south shore of Santorini, with the port of Eleusis, collapsed beneath the sea. Mikra Kameni appeared in 1573, and Nea Kameni in 1707–11. In 1866 a protracted eruption lasted for two years, observed by the French geologist and archaeologist, Ferdinand Fouqué, whose book Santorini et ses Eruptions, is a mine of information on the island's past volcanic activity: an island, named Aphroessa, appeared in 1868 and then disappeared again. The eruptions of 1925/6 joined Mikra and Nea Kameni into a single land mass. There were further eruptions in 1939/40 and 1950; and in July 1956, an earthquake destroyed or damaged more than half the buildings in the towns of Oia and Firá.
From the (usual) point of disembarkation on the north side of Nea Kameni, which corresponds to the area of the island which first appeared in 1570, a path leads up to the summit above the central crater of the volcano, which exhibits little visible activity beyond the escape of a strong and stinging sulphurous vapour. Nothing lives or grows on the island. Close to the shore, the land mass is formed of boulders of shiny, black basalt with forms that are alternately slickly rounded and jagged-edged. From the summit, the cooled magma flows of the last major eruptions can be distinguished: the 1707–11 deposits to the northwest; the main 1925–28 deposits to the east; and the massive areas of the 1866–70 deposits to the south. On the surface to the west the superimposed lava flows of 1925–28 can be seen. Warm springs rise under water at several points near both Palaia and Nea Kameni.
Info: McGilchrist's Greek Islands
(From McGilchrist’s Greek Islands, © Nigel McGilchrist 2010, excerpted with his gracious permission. Click for the books)