Nisyros: The Sleeping Giant of the Dodecanese

The youngest of Greece's volcanos, Nisyros is also the most captivating – an endless source of fascination for scientists and inspiration for artists and inquisitive travelers. Visualize the scene: above the Aegean Sea, the war between the Giants and the Olympian Gods is raging. Poseidon, the god of the sea, is giving chase to a giant by the name of Polyvotis. When he finally catches up with him, near Kos in the south-east, he uses his trident to tear off a chunk of the island, which he then catapults on top of Polyvotis. This piece of Kos becomes the island of Nisyros, trapping the hapless giant underneath – an eternal prisoner of the Olympians, forever groaning and puffing in anguish in his effort to break free. This is at least how the ancient Nisyrians sought to explain both the regular earthquakes occurring on their island and the fumes that rose from the earth. Modern science, of course, has a different story to relate: one about a volcano that, having started its life underwater, started to emerge from the sea about 150,000 years ago. Over the next 135,000 years, a series of magmatic eruptions both great and small formed an island-volcano similar in shape and size to the Nisyros we know today.  When Neolithic man inhabited the island some 6,500 years ago, all magmatic activity – the result of which is molten rock – had ceased. The only eruptions witnessed by those primitive people, and all subsequent inhabitants in historical times, were hydrothermal. These occur when the hot fluids under the earth’s surface produce so much steam that the layers of rock buckle under both the pressure and the concurrent earthquakes, popping like the lid of a pressure cooker and expelling steam, gas, mud and rock. Hydrothermal eruptions are not as catastrophic as magmatic ones, but they must have been as frightening, judging from the account of French geologist Henri Gorceix, who witnessed one in 1871: “After a violent quake the villagers of Nisyros heard crashes as loud as thunder; red and yellow flames leapt into the air, higher than the island’s loftiest peaks, falling back into the sea; the fields at the base of the original crater were covered in white dust. That same night, huge fumaroles opened up and since then have not ceased to vomit forth their fumes.” The “legacy” of all those hydrothermal eruptions to future generations were the circular craters that are nowadays so popular with tourists. Of the 20 traced on the island, the largest, most imposing and most visited of all is the approximately 4,000-5,000-year-old Stefanos, known simply as “the volcano.” Elliptical in shape, with a diameter ranging from 260m to 330m and 27m deep, Stefanos is in fact one of the largest and best preserved hydrothermal craters in the world. Its fumaroles (the holes in the ground) are still puffing hydrogen sulfide and the water under the surface boils at corrosive temperatures. This serves as a reminder that even though Nisyros has not given any indication of magmatic activity for thousands of years, it is, nonetheless, a potentially active volcano. Therefore, a hydrothermal eruption following an earthquake is not out of the question. This is why there is a permanent observatory on the island to monitor earthquakes and volcanic activity. see full article here