CALDERA – CRATER
The volcano of Nisyros is the newest active volcano in Greece since its oldest rocks do not exceed 150,000 years of age. 60,000 years ago to this day, hundreds of small eruptions built a cone that rose about 600 metres above sea level and had roughly the perimeter of the island as it is today.
Two huge explosions, 25,000 and 15,000 years ago, destroy the central part of the volcano, which caves in and creates the current caldera of the volcano. Since then the volcano remains at rest. But the hot rocks, located a few kilometres in depth underneath the caldera and their hot gases, warm the seawater and the rainwater that circulates around the more shallow rocks and convert it into superheated liquid at temperatures approaching the 500 degrees Celsius. Intermittently, the superheated liquid ejects into the air the rocks that prevent it from reaching the surface, causing hydrothermal explosions and creating hydrothermal craters. Such explosions were recorded in Nisyros in historical times.
The center of the island is dominated by the caldera of Nisyros. Its diameter is about 4 kilometers, its ledge ranges in altitude between 250 and 600 meters, while its bottom is at 100 meters from the sea level. Its west-northwestern part is surrounded by the hills Mporiatikos, Nifios, Profitis Elias and Trapezina. Traces of 20 craters have been detected inside the caldera, 10 of which are well preserved and each one has its own name. The settlements of Emporios and Nikia offer a magnificent view of the caldera, and the view from Prophitis Elias in Nikia in particular will astonish you.
Stefanos is the largest and most impressive of the 10 craters and monopolizes the interest of visitors, as it seems to them that this is the “volcano”. It is one of the largest and best-preserved hydrothermal craters in the world, it has ellipsoid shape with its longer axis at 330 meters and the smaller at 260 meters, while its depth reaches 27 meters. We don’t know its exact age, like with most craters, but it is calculated that it can’t be more than 3,000 to 4,000 years old. Every visitor can follow a trail to reach the inside of the crater and admire the space and its unique steam activity up-close.
STEAM ACTIVITY ON CRATER STEFANOS:When the rainwater enters the inside of the crater, a few meters below its surface, it encounters temperatures above 100 degrees Celsius and starts to heat and turn into steam. The steam pressures the surface of the crater, causing small explosions and creating round funnels, the holes that exist in the crater. Along with the steam, other gases come out, such as hydrogen sulfide which produces the distinctive smell that prevails in the area.
Next to Stefanos lies a smaller crater, the small Stefanos. The two older distinguishable hydrothermal craters are the kaminakia, beneath Nikia. Each of them has a diameter of 150 meters. The rest hydrothermal craters are situated in the area of Lofos, across from the crater Stefanos. There you can find Logothetis, the oldest crater in the region, Polyvotis with a diameter of 300 on 150 meters, small Polyvotis, the outcome of the latest hydrothermal explosion in 1887, Alexander, Achilleas and Logothetis.
Palaiokastro is the fortress of the ancient city of Nisyros and one of the best preserved in the Aegean area. The ancient city was built at least since the 8th century BC, above the modern settlement of Mandraki. The wall, as it survives today, dates back to the 4th century BC. Built on the brow and the slopes of the hill it led to the cliff from its west side, whilst from its north, it reached up to the rock where the medieval castle and the monastery of Panagia Spiliani lie today. The total length of the fort is very large. The wall and the cliff mark an area of approximately 130.000 m2, with total perimeter of almost 2 km, while the weight of some of the stones that make up the wall reaches 3.5 tons. The construction of the costly and strong fortifications could be attributed to the effort of the tyrant of Caria Mausolus and his successors, who for a short time (355-332 BC) had acquired control of Rhodes, Kos, and the neighbouring islands, to create a powerful defensive front in the region. The local volcanic black stone (basaltic andesite) was used for its construction. Palaiokastro is located in the village of Mandraki and the admission is free
Built on tall rock at the Castle of Mandraki is the monastery of Panagia Spiliani. According to tradition, in 1400 AD a farmer discovered a small picture of the Virgin Mary, which he brought to the Church of Panagia Potamitissa. A few days later, the picture disappeared only to be found later in a cave at the top of a large rock. The inhabitants returned it to the church but the incident was repeated. For this reason it was decided to build the cave as a church and it was done so a few years later. Going up the 130 steps, the visitor arrives at the holy cave and sees the remarkable wooden altarpiece from 1725 AD. On the altarpiece, images of Jesus, Virgin Mary with the Holy Child and the Assumption of Virgin Mary and St. Charalambos are visible. The image of the Virgin Mary, padded by silver, is double-faced: on the back it features St. Nicholas and on the other side the Virgin Mary with the Holy Child, crafted with the style of the russian school. It is said that in Virgin Mary’s left hand lies the little picture that had been discovered in the 13th century AD. The picture is miraculous, and that is why on the 15th of August crowds of pilgrims visit the island.
It consists of two hills that are joined together by a narrow isthmus. The southwestern part of the island is composed of thick layers of pumice, which are deposited there by two explosions after the formation of Nisyros. The first eruption left on shallow seas over 160 meters of thick layers of pumice, which the company LAVA Mining & Quarrying exploits since 1956. The second explosion leaves a layer of pumice stone 3-4 meters thick in Gyali while it also covers Nisyros with pumice stones that are almost a meter thick.
The northeastern part of the island is composed entirely of thick natural streams of glass (hence the name of the island), like the well-known obsidian and perlite.