Geology of Milos: Milos is part of an area called the South Aegean Volcanic Arc. This arc is an alignment of volcanoes, which were formed by the subduction of the African plate beneath the Eurasian plate. This arc encompasses the Gulf of Korinthos and the west coast of Turkey. It consists of the volcanic centers of Methana, Milos, Santorini and Nisyros, as well as a number of submarine volcanic structures (such as the active Columbo, near Santorini). The Arc has been active for 4.7 million years. The Milos district includes Milos, Kimolos, Antimolos and Poliegos.
This volcanic activity explains why there is so much obsidian in Milos. Andesitic rocks can be found in the southwest portion of the island, too.
There are both volcanic domes and dikes in Milos that come from the thermal cooling of lava. This cooling created the islets of Glaronisia and Kalogeros. The volcanic rocks found in Milos were the result of extreme hydrothermal activity. This activity changed the chemical composition of the original rocks. It caused the formation of a large ore deposit of clay minerals.
These clay minerals have hugely benefited the economy of Milos. The island helped Greece become the second-largest world producer of bentonite, a clay mineral.
The alterations due to volcanic activity are the reason behind the extreme colors and landscapes. It also created the beaches of Firiplaka, Firopotamos, and Plathiena. The volcanic nature of Milos is due to the heat flux in the crust of the earth in this area.
If you are interested in Geology, you can visit the Mineralogical Museum of Milos which is located 1 km from the port of Adamas.