Santorini, Greece


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Location

santorini-overview-with-insert

Greece as a whole is a seismically active area and Santorini Island is no exception to the rule. The image below shows the seismicity during 2012 to May 20. You can click the image for the latest version.

Unless otherwise stated the sources for this material are Smithsonian and Wikipedia: Santorini or Wikipedia: Santorini caldera.

In about 1630 BC there was a cataclysmic eruption that formed the caldera that makes up the Santorini Islands today. This eruption, known as the Thera eruption, is reputed to be responsible for the destruction of the Minoan civilisation and the legends of Atlantis.

The steep inner walls of Santorini, capped by whitewashed villages, drop steeply into the caldera bay, forming one of the scenic highlights of the Aegean. Pyroclastic-flow deposits from four caldera-forming eruptions dating back to 100,000 years ago are exposed in the caldera walls in this north-looking view. The youngest caldera was formed about 3500 years ago during the noted Minoan eruption of Santorini. The flat-topped peak on the left skyline is Skaros, a remnant of a shield volcano constructed within a previous caldera.

Photo by Lee Siebert, 1994 (Smithsonian Institution).

The circular island group is composed of overlapping shield volcanoes cut by at least four partially overlapping calderas. The oldest southern caldera was formed about 180,000 years before present (BP), followed by the Skaros caldera about 70,000 years BP, and then the Cape Riva caldera about 21,000 years BP. The youngest caldera formed about 3600 years BP during the Late-Bronze-Age Minoan eruption that forced abandonment of the thriving Aegean Sea island. Post-Minoan eruptions beginning in 197 BC constructed a series of lava domes and flows that form two islands near the center of the caldera. A submarine eruption took place in 1650 AD outside the caldera NE of Thera. The latest eruption at Santorini produced a small lava dome and flow in 1950, accompanied by explosive activity.

Santorini is essentially what remains after an enormous volcanic explosion that destroyed the earliest settlements, on a formerly single island, and created the current geological caldera. A giant central, rectangular lagoon, which measures about 12 by 7 km (7.5 by 4.3 mi), is surrounded by 300 m (980 ft) high, steep cliffs on three sides. The main island slopes downward to the Aegean Sea. On the fourth side, the lagoon is separated from the sea by another much smaller island called Therasia; the lagoon is connected to the sea in two places, in the northwest and southwest. The caldera being 400m deep makes it possible for all but the largest ships to anchor anywhere in the protected bay; there is, however, a newly built marina in Vlychada on the southwestern coast. The principal port is called Athinias. The capital, Fira, clings to the top of the cliff looking down on the lagoon. The volcanic rocks present from the prior eruptions feature olivine and have a notably small presence of hornblende.[2]

It is the most active volcanic centre in the South Aegean Volcanic Arc, though what remains today is chiefly a water-filled caldera. The volcanic arc is approximately 500 km (310 mi) long and 20 to 40 km (12 to 25 mi) wide. The region first became volcanically active around 3–4 million years ago, though volcanism on Thera began around 2 million years ago with the extrusion of dacitic lavas from vents around the Akrotiri.

The island is the site of one of the largest volcanic eruptions in recorded history: the Minoan eruption (sometimes called the Thera eruption), which occurred some 3600 years ago at the height of the Minoan civilization. The eruption left a large caldera surrounded by volcanic ash deposits hundreds of feet deep and may have led indirectly to the collapse of the Minoan civilization on the island of Crete, 110 km (68 mi) to the south.

The island is the result of repeated sequences of shield volcano construction followed by caldera collapse.[10] The inner coast around the caldera is a sheer precipice of more than 300 m drop at its highest, and exhibits the various layers of solidified lava on top of each other, and the main towns perched on the crest. The ground then slopes outwards and downwards towards the outer perimeter, and the outer beaches are smooth and shallow. Beach sand colour depends on which geologic layer is exposed; there are beaches with sand or pebbles made of solidified lava of various colours: the Red Beach, the Black Beach, the White Beach, etc. The water at the darker coloured beaches is significantly warmer because the lava acts as a heat absorber.

The caldera is composed of overlapping shield volcanoes, cut by at least four partially overlapping calderas, of which the oldest southern caldera was formed about 180,000 years before the present era (BP). The subsequent Skaros caldera was created about 70,000 years BP, and the Cape Riva caldera about 21,000 years BP. The current caldera was formed about 3600 years BP during the Minoan eruption.[4]

Palea Kameni and Nea Kameni were formed as a result of multiple, initially submarine eruptions at the center of the caldera.[5]

Although dormant, Santorini is an active volcano. Numerous minor and medium-sized, mainly effusive eruptions have built the dark-colored lava shields of Nea and Palea Kameni inside the caldera.

Their last eruption was in 1950, and now only fumarolic activity, primarily inside the recently active craters, takes place. GPS instruments have registered renewed deformation around the caldera in 2011 and 2012.

The huge Minoan eruption of Santorini in the 17th century BC was rated 7, the highest score for a historical eruption, in the Smithsonian Global Volcanism Program’s Volcanic Explosivity Index.

Eruptive history
Start date Stop date Characteristics of eruption
1610 BC ± 14 years
(“Minoan” eruption)
Unknown Central vent eruption, regional fissure eruption, submarine eruption, explosive eruption, pyroclastic flows, phreatic explosions, fatalities, extensive physical damage, mudflows, tsunami, caldera collapse, evacuation.
197 BC Unknown Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption.
Dec 31, 46 AD Feb 1, 47 AD ± 30 days Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, lava dome extrusion, tsunami.
Jul 15 726 AD ± 45 days Unknown Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, lava dome extrusion, damage.
1570 1573 Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, lava dome extrusion.
Sep. 27, 1650 Dec. 6, 1650 Flank (excentric) vent, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, fatalities, damage, tsunami.
May 23, 1707 Sep. 14, 1711 Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, lava dome extrusion, damage.
Jan. 26, 1866 Oct. 15, 1870 Central vent eruption, regional fissure eruption, submarine eruption, new island formation, explosive eruption, lava flows, lava dome extrusion, fatalities, damage, evacuation.
Aug. 11, 1925 Mar. 17, 1928 Central vent eruption, regional fissure eruption, explosive eruption, phreatic explosions, lava flows, lava dome extrusion.
Aug. 20, 1939 Jul. 2, 1941 ± 1 day Central vent eruption, regional fissure eruption, submarine eruption, explosive eruption, phreatic explosions, lava flows, lava dome extrusion, damage.
Jan. 10, 1950 Feb. 2, 1950 Central vent eruption, regional fissure eruption, submarine eruption, explosive eruption, phreatic explosions, lava flows, lava dome extrusion.

Recent news items about Santorini volcano

Science News: Greek volcano reawakens
Crystals Improve Understanding Of Volcanic Eruption Triggers

The team, from Durham University and the University of Leeds, studied crystal formation from a volcano, in Santorini, in Greece, to calculate the timescale between the trigger of volcanic activity and the volcano’s eruption.

Weather and Web Cams

Webcam pages are notorious for changing. If a link is broken please let me know in the comments section. Last checked 01 August 2015

Weather Information Sites

Web Cam Sites

Details of the Greek GPS monitoring network can be found here. This is provided purely for interest as there is no coverage (apparently) of the Santorini or Crete areas by this network. There is coverage it would seem but we do not have access. This picture from the Science News article linked about shows a GPS station on Santorini.

Seismicity and Seismograms


Real Time Seismicity in Greece for the last 48 hours ( Automatic Alerts )

Seismogram thumbs start at caldera centre and then across to THR5 and on round in a clockwise direction. These thumbnails are realtime and can be refreshed by refreshing the page.

THR3 Kammeni Station
THR3 Kammeni Station
THR5 Kera Station
THR5 Kera Station
SAP3 Portable
Portable SAP3
SAP4 Portable
Portable SAP4
CMBO Columbo
CMBO Columbo Station
THR2 Vourvoulos Station
THR2 Vourvoulos Station
THR7 Impis Station
THR7 Impis Station
SAP2 Portable
Portable SAP2
THR8 Monolithos Station
THR8 Monolithos Station
THT1 Athinios Temporary (Pelekanos) Station
THT1 Athinios Temporary (Pelekanos)
SANT Santorini Station
SANT Santorini Station
THR6 Acrothri Station
THR2 Acrothri Station
SAP1 Portable
Portable SAP1

Seismograph Stations not located on Santorini

MN.IDI Anogia, Greece (Crete) ~132km from Santorini

HL.ARG Archaggelos, Rhodes, Greece ~245km from Santorini

HL.ITM Ithomi, Messinia, Greece ~322km from Santorini

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