Introduction

Nissyros Volcano is an active volcano located at the southeastern end of the South Aegean , dodecanese islands Greece.
Nissyros is an 8 km-wide island located at the eastern end of the Hellenic island arc, 340 km SE of Athens. Nissyros Island is part of the Kos-Yali-Nissyros Volcanic Field in the SE part of the Aegean Sea. The Hellenic Volcanic Arc is a magmatic expression of the active northeastward-directed subduction of the African Plate beneath the Aegean Plate.

Nisyros Island has an average width of 8 km, and covers an area of about 42 sq km. The volcano contains a 3.8 km-wide caldera.
Historical activity of Nissyros volcano produced phreatic eruptions in the caldera. Currently fumarolic activity occurs in the caldera, and hot springs are found on the coast. The volcano has erupted at least 13 times during recorded history.
2003 Unrest
In January 2003 the crater was declared off limits due to increasing temperatures and growing surface cracks. Temperatures of the hydrothermal system increased from 210 to 315 degrees C.
2001 Lakki Plain Fracture
On 20th November 2001 a ground fracture opened up in the central part of the Lakki Plain. The fracture was up to 5 m wide, 10 m deep, and was 350 m long. One year later (December 18, 2002), the rupture extended southwards for another 250 m. The sudden fracturing was caused by stress release without producing
any seismic activity.
Seismic Crisis 1995-1998
A volcano-seismic crisis on Nissyros occurred between 1995 and 1998, and was accompanied by 14 cm of ground uplift on the island. More than 1600 seismic events were located within the Kos-Nisyros-Tilos area. Several shallow tectonic earthquakes at depths up to 10 km with larger magnitudes up to 5.5 occurred along the fault system between Tilos and Kos.
1873 Eruption
During the latest hydrothermal explosion in 1873, fire and gas eruptions were reported along the coast near the town of Mandraki.

Nissyros Volcano Eruptions
1888, 1873, 1871, 1422

Location: 36.4 N, 27.1 E
Height: 2,290 feet (698 m) above sea level

The island of Nissyros is a stratovolcano at the eastern end of the Greek island arc. This arc of volcanoes is related to the northward subduction of the African plate beneath the Aegean microplate. Santorini, a better known volcano, is west of Nissyros.

The base of the island is made of hyaloclastite, lava flows, and breccias, mostly of andesite composition. These rocks are capped by pyroclastic deposits and volcanic domes of dacite composition. The pyroclastic deposits are related to two explosive phases of the volcano. Each phase was Plinian in character, producing tall column of ash as high as 9-12 miles (15-20 km) above the volcano. The collapse of the tall columns of ash made the pyroclastic deposits. The volume of magma erupted was great enough to cause the summit of the volcano to collapse, making a caldera. The two explosive phases were probably several thousand years apart and occurred roughly 25,000 years ago. After the caldera formed, eruptions produced the lava domes.

A great depression, Rammos and Laki (shown in the above photo), is located just east of the center of the island. The west rim of this depression is formed by St. Elias, the highest point on the island. St. John mountain is on the east side of the depression. The depression is steep sided and its bottom is about 300 feet (100 m) above sea level. Stefanos, a small explosion sink, is at the far end of the valley. This view is from the north.

Stefanos (shown above) is one of five small explosion sinks along the south part of the depression. Stefanos is about 1,000 feet in diameter (300 m) and 80 feet (25 m) deep. Alexandros, an explosive vent, is just beyond Stefanos in the photo. Two dacite domes, St. Elias (left) and Nifios (right), form the west wall of the depression.

This photograph shows the wall of the Stefanos explosion sink.

Close up of Alexandros, an explosive vent on the southeast edge of the St. Elias dome.
It is suspected that the volcano erupted in 1422. In 1871, an eruption was accompanied by earthquakes, detonations, and red and yellow flames. Ash and lapilli were erupted and covered the floor of Rammos, destroying the fruit gardens there. During a three-day-long eruption in 1873, a 20-25 foot (6-7 m) diameter crater formed and ash and blackish mud was ejected. The bottom of Laki and Ramos was transformed into a lake by hot saline water that overflowed the crater. The most recent eruption was in 1888. This strong eruption threw out a cylindrical pipe of volcanic material at least 80 feet (25 m) in diameter. Mud, lapilli, and steam were also ejected. In 1956, fumaroles were observed along the west and south sides of Rammos .

More Info