Volcano is the open passage from the inside of the Earth that allows the flowing or explosion of fluid rocks and gases from the inside (mantle) to the surface of the solid cortex in the form of a lava. This activity leads to the creation of a mountain, which we call the volcano in our everyday language.

In Greece the active volcanoes are arranged in a arc (Greek volcanic arc) and include from the West to the East the following volcanoes: Sousaki, Methana, Milos, Santorini, Giali, Nisyros and Kos.

Slightly older and no longer active is the volcano activity in the following places: N. Vlychades (North Evian Gulf), Mikrothives (N. Magnesia), Northern Sporades and Almopia. Extensive volcanic activity in the Aegean Sea (Lemnos, Lesvos, etc.) has caused the deposition of many formations and the creation of the fossilized forests in these islands.

South of Crete, under the blue sea, the African plaque is under the European. Where the African plaque thins, magma finds the opportunity to go out.

All Aegean volcanoes are cone-shaped and have been corrupted either by erosion, as in Milos, or by “calderization”, that is, it has sunk due to a great explosion, such as in Santorini. Despite small-scale explosions occurring at a shallow depth, scientists do not expect large explosions, but an increased earthquake-volcanic activity.

The last great explosion in Santorini occurred around 1,630 BC. and created the great caldera in the center of the island complex. There followed other smaller scale explosions, slightly changing the landscape, with the last in 1939-41 and 1950. Santorini has the largest caldera of the world with a height of 300 m and a diameter of 11 km.

Today, the underwater volcano “Kolumpos” off the NE of Santorini is considered to be more dangerous, since its activity was in the past catastrophic. 350 years ago, 70 inhabitants and 1,000 animals died on the island, not from the explosion, but from the invisible, odorless poisonous gases that had been emanating from the volcano for six months.

The volcano of Nisyros consists of a large caldera in which there are 5 smaller craters. It has one of the world’s largest calderas, 650 m high and 3000 m in diameter.

At Sousaki, near the Agioi Theodoroi of Corinth, there is a volcano, 180 m high, with the last volcanic activity in the area 2.7 million years ago. However, there is still very intense post-volcanic activity with the emission of hot gases, mainly carbon dioxide, methane and hydrogen sulphide. Gas disintegration produces impressive formations, while many animals in the area have been spoiled by poisonous gases. The hot springs in Loutraki are connected to the magical chamber of Sousaki.