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Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Articles avec #historical eruptions catégorie

Publié le par Bernard Duyck
Publié dans : #Historical eruptions

The cycling Tour de France  has just passed the passes of the Pyrenees, and it's time to talk about the regional volcano, the Pic du Midi d'Ossau.

This proud Béarn volcano, close to the border with Spain, remains an exceptional case in the Pyrenees.

The Pic du Midi d'Ossau, from Lake Gentau - Photo Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

The Pic du Midi d'Ossau, from Lake Gentau - Photo Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

 Topographic map of the western central Pyrenees. - Doc. Capbourrut

Topographic map of the western central Pyrenees. - Doc. Capbourrut

The region is rich in 400 million years of geological history, from the Devonian series to the glacial reliefs which give their forms to the current valleys:

* from -410 to -360 Ma: it is occupied by a tropical sea of ​​the southern hemisphere. In particular limestones are formed there (Pic Castérau, Pène Peyreget)

* from -360 to -290 Ma: this is the period of collision and the formation of a mega-continent, "Pangea"; the world-wide Hercynian mountain range is forming. The previously formed sedimentary series are folded (fold of the Pic Castérau, visible when we go around the lakes)

The Pic du Midi d'Ossau, south face - Photo Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

The Pic du Midi d'Ossau, south face - Photo Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

* from -300 to -250 Ma: the Hercynian range undergoes erosion. The volcanism of Ossau and Anayet takes place in a phase of extension which follows the Hercynian compression.

During the Permian, the formation of grabens and the opening of fractures causes the rise of the deep magma from the upper mantle, thus forming a magmatic chamber which flows out on the surface and constitutes the Ossau volcano. The volcanism of Ossau takes place in Autunian in two episodes dated at 278 ± 5 and 272 ± 3 Ma.

Formed of andesite, the volcano sees prolonged emissions of volcanic lava gradually emptying its magmatic chamber. During an eruption - certainly very violent - the roof of the volcano collapses in the magma chamber, constituting the caldera. The volcanic activity then resumes through marginal cracks at the level of this caldera, which form the annular wall made up of dacite and rhyolite. The body of the Pic du Midi d'Ossau then forms at the level of this ring. The volcanic activity of Ossau ceased in the Permo-Triassic, about 250 million years ago.

The Permian continental deposits bear witness to a hot and arid continent.

The Ossau caldera before the formation of the Pyrenees and its deformation during the establishment of the mountain range - Doc. Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

The Ossau caldera before the formation of the Pyrenees and its deformation during the establishment of the mountain range - Doc. Capbourrut / Personal work, CC BY-SA 4.0, commons.wikimedia.org

* from -250 to -100Ma: the Iberian plate on which we are in Ossau probably remained emerged to be finally invaded by the sea. Massive limestones settle there.

 

* from -60 Ma: the collision of the Iberian and European plates leads to the formation of the present-day Pyrenees. The Ossau caldera is dislocated in the overlaps caused by compression.

Several intrusive arches can still be identified: the Moundelhs arch, the Peyreget arch, and the Ayous arch. The Pic du Midi d'Ossau is part of the intrusive arc of Moundelhs, the peak forms a laccolite, that is to say a very significant thickening of the annular vein. During the formation of the Pyrenees, this laccolite is tilted and then lifted to a height much higher than the rest of the old caldera. The Moundelhs arc overlaps that of Peyreget at the level of the Peyreget pass, a central area of ​​about 200 ha is emerging between these two arches, at the level of the Embarradère and Moundelhs cirque. This space represents the heart of the caldera, the crater of the Ossau volcano

 

* from -2.6 Ma, period during which homo habilis fished its first tools, to -12000 years: glaciations model the Pyrenean landscapes.

 

Below is a summary in pictures of the geological history of the Pyrenees, provided by the Parc Nationla des Pyrénées. Good reading.

 

Sources:

- BIXEL F. (1984) - The Stephano-Permian volcanism of the Pyrenees. Thesis. Toulouse.

- Information saga - Birth, life and death of a volcano: the paleovolcano at Pic du Midi in Ossau Dominique Rossier, member of SAGA.

- L'Ossau, from Bious Artigues to the lakes of Ayous 2019 UTLA - geology course in the field in partnership with GéolVal

- Pyrenees National Park.

The Ossau volcano - Doc. Pyrenees National Park

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Publié le par Bernard Duyck
Publié dans : #Historical eruptions
 Volcanic landscape of the Snake river near Twin Falls - archives © Bernard Duyck 2009

Volcanic landscape of the Snake river near Twin Falls - archives © Bernard Duyck 2009

A team of researchers led by Thomas Knott, a volcanologist at the University of the United Kingdom in Leicester, examined deposits in southern Idaho, combining different techniques to analyze rocks, including mineral chemistry, data palaeomagnetic and field characterizations.

This study led to the discovery of two new super-eruptions on the path to the Yellowstone hot spot dated 8.99 and 8.72 Ma, which were overlooked because they were attributed to small units located in the Snake River plain (SRP).

Map of the northwest of the USA with the position of the volcanic fields of the yellowstone hotspot (in orange) and the basalts of the Columbia river (in gray) - Doc. USGS

Map of the northwest of the USA with the position of the volcanic fields of the yellowstone hotspot (in orange) and the basalts of the Columbia river (in gray) - Doc. USGS

The McMullen Creek eruption, dated approximately 8.99 Ma, was magnitude 8.6, larger than the last two major eruptions in Yellowstone, Wyoming. Its volume exceeds 1,700 km³, covering ≥12,000 km².

The Grey's Landing eruption, dated 8.72 Ma, was even larger, with a magnitude of 8.8 and a volume ≥2800 km³, covering ≥23000 km². It is the largest and hottest documented eruption of the Yellowstone hotspot.

Simplified PRS map in effect before this study - the Twin Falls / Picabo area will need to be reviewed

Simplified PRS map in effect before this study - the Twin Falls / Picabo area will need to be reviewed

These discoveries reduce the number of eruptions by a third during the "Yellowstone hot spot push" in the Miocene by a third, but increase the number of super-eruptions by two units.

In addition, they indicate that the size, frequency and temperatures of placement of super-eruptions have decreased over time ... all these characteristics suggest that the activity of the hot spot may decline.

Since then there have been the eruptions of the Yellowstone caldera, the last explosive eruption of which was around 640,000 years ago, followed by about 80 lesser eruptions, "relatively non-explosive" (USGS).

All this does not tell us about the time of a next possible eruption at Yellowstone, the volcano remains meanwhile under the supervision of the USGS / Yellowstone Volcano Observatory, in normal level and green aviation code.

Landscapes to discover as soon as travel is permitted again.

The Snake river at Twin Falls - archives © Bernard Duyck 2009

The Snake river at Twin Falls - archives © Bernard Duyck 2009

Sources:

- Geology - JUNE 01, 2020 - Discovery of two new super-eruptions from the Yellowstone hotspot track (USA): Is the Yellowstone hotspot waning? - By Thomas R.Knott & al - https://doi.org/10.1130/G47384.1

- Yellowstone Volcano Observatory - link

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Publié le par Bernard Duyck
Publié dans : #volcanic activity, #Historical eruptions

Geologists from the Geologische Dienst Nederland (GDN) have discovered in recent studies a new volcano in the subsoil of the North Sea northwest of the island of Texel (Friesian archipelago).

He was baptized Mulciber, "who wields iron", one of the nicknames of Vulcan, the Roman god of fire and volcanoes.

 Respective location of Zuidwal and Mulciber volcanoes. - Doc.TNO

Respective location of Zuidwal and Mulciber volcanoes. - Doc.TNO

Since 1985, volcanic ash had been discovered during drilling. Until recently attributed to the Zuidwal volcano (see related article), located in the Wadden Sea northeast of Texel and a hundred kilometers away, the new volcano was discovered during an investigation into the rock layers of the Upper Jurassic, under several kilometers of sediment, at 3,000 meters below sea level. These two volcanoes had a brief activity around 150 million years ago.

Mulciber Volcano - The top of the basalt layer imaged using 3D seismic, about 3 km deep. The red elevation shows the location of the volcano itself. In the seismic section, we can see that younger overlying rocks are bent over the volcano (Source: TNO)

Mulciber Volcano - The top of the basalt layer imaged using 3D seismic, about 3 km deep. The red elevation shows the location of the volcano itself. In the seismic section, we can see that younger overlying rocks are bent over the volcano (Source: TNO)

Striking deviations in the structure of the subsurface and the Earth's magnetic field at the site, together with the presence of basalt, made one think of a new volcanic structure. The 3D images suggest the structure of the volcano.

The strong positive deviation from the normal geomagnetic field is caused by the large concentrations of magnetic minerals, such as iron oxide and magnetite, common in volcanic rocks. It is comparable to that encountered at the Zuidwal volcano.

The volcanism of the place can be explained by the tectonic processes resulting from the disintegration of the Pangea supercontinent, with rifting, with which volcanism is often associated. Jurassic rifting did not continue in the North Sea, but the magma which rose may have created deposits of igneous rocks and volcanism. Then, the upheavals continued in the upper Cretaceous (100 to 66 Ma) with the inversion of the grabens of the south of the North Sea, in probable link with the Alpine orogeny, and the collision between the African and European plates.

Jurassic volcanism in the North Sea - tectonic reconstruction by Douwe van Hinsbergen and Eldert Advokaat from the University of Utrecht, illustrating the context in which the newly discovered and extinct Mulciber volcano and the already known Zuidwal volcano were active some time ago about 150 million years ago. - Doc. Michiel van der Meulen / Viméo

This brings the number of Dutch volcanoes to four: two extinct in the North Sea and two active in the Caribbean, the Mount Scenery in Saba (GVP / https://volcano.si.edu/volcano.cfm?vn=360010) and the Quill in Saint-Eustache (GVP / https://volcano.si.edu/volcano.cfm?vn=360020).

 

Sources: Thanks to my daughter Frédérique for the info (which makes her win an intra-family challenge 2020)

- Media: 7 of 7; RTL News; ad, nl

- TNO, nl - TNO discovers a volcano 150 million years old in the North Sea.

- Wetenschap.nu - Discovery of a new volcano in the Dutch basement after Geert-Jan Vis

- Global Volcanism Program - Saba and Quill

- The dismemberment of Pangea: from Jurassic to the present day - http://www2.ggl.ulaval.ca/

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Publié le par Bernard Duyck
Publié dans : #Historical eruptions
  St Helens, seen from the west, with Mt. Adams in the background; in the center, the S.Fork Toutle river valley - photo Rick Hoblitt 1979 - USGS

 St Helens, seen from the west, with Mt. Adams in the background; in the center, the S.Fork Toutle river valley - photo Rick Hoblitt 1979 - USGS

40 years ago, a striking eruption started at St Helens.

The Global volcanism Program characterizes it by an VEI of 5, and a duration from March 27, 1980 to October 28, 1986 ± 3 days.

Here is the activity at the end of March:

At dawn on March 28, pulses of dark, dense ash rise 3 km above the summit and some blocks are ejected. Small mudslides move in impulses and surge along the northeast flank, reaching the timber line in the middle of the afternoon. Occasional periods of rhythmic ash emission, lasting from 45 minutes to 1 hour, occurred throughout the day, and more low-temperature ash avalanches traveled the N and NE slopes. Many earthquakes have occurred, including one of M 4.2, concentrated in an area about 2 km deep in the northwest quadrant of the volcano.

As of that evening, the water level in the reservoir of Swift Lake was lowered by at least 8 m as a precaution, to take into account any runoff of snowmelt or mudslides induced by the eruption.

St. Helens -  fault cutting EW the top and bulge on the side N- photo 27.03.1980 Frank David / USGS

St. Helens -  fault cutting EW the top and bulge on the side N- photo 27.03.1980 Frank David / USGS

A new crater 30 to 50 m in diameter, about 10 m from that formed on March 27, was discovered during overflights on March 29.

A blue flame was observed in the vents, sometimes flickering and jumping from one crater to another. No strong ash pulse was reported between the explosions on March 28 at 11:00 p.m. and March 30 at 4:10 a.m.

During this period, the earthquakes appeared to migrate to the SSE along a linear trend of 25 km, extending from 2 km deep in the northwest quadrant of the volcano 15-20 km deep below the Swift reservoir, at the S foot of Mt. St. Helens. However, continued analysis of the seismic data indicated that apparent migration could be an artifact of the data reduction and of the crustal model used. The refinement of the epicenter determinations is in progress.

The summit of St. Helens after several small eruptions: two small pit craters formed on March 27, 1980 - photo Robert Krimmel 30.03.1980 / USGS

The summit of St. Helens after several small eruptions: two small pit craters formed on March 27, 1980 - photo Robert Krimmel 30.03.1980 / USGS

Reporters appear in three-piece suits with letters of reference from the Washington Post, New York Times, Los Angeles Times and National Geographic, chatting with each other about other volcanoes they had covered in the Aleutian Islands of Alaska and Guadaloupe . The media is ready for a disaster, for another Pompeii or Atlantis, perhaps lava flows invading Portland. But the apocalypse refuses to cooperate. There is no lava.

 St Helens- Oregonian Journal (Portland, Oregon) page 10 of March 29, 1980

 St Helens- Oregonian Journal (Portland, Oregon) page 10 of March 29, 1980

Sketch of the map of Mt. St. Helens. The positions and lengths of the arched top cracks are approximate, as indicated by question marks at each end. The old summit crater is shown to be about 0.5 km larger than its actual diameter. The two active vents have merged to the surface, but retain their distinct identities. - March 1980- Courtesy of Robert Christiansen and Robert Tilling / GVP

Sketch of the map of Mt. St. Helens. The positions and lengths of the arched top cracks are approximate, as indicated by question marks at each end. The old summit crater is shown to be about 0.5 km larger than its actual diameter. The two active vents have merged to the surface, but retain their distinct identities. - March 1980- Courtesy of Robert Christiansen and Robert Tilling / GVP

Strong activity resumed on March 30. At 0740 hrs, an anvil-shaped cloud of ash and vapor developed, producing ash falls as far as Bend, Oregon, about 250 km south. The cloud can be seen on high resolution NOAA weather satellite images, but the altitude of its top could not be estimated from satellite data.

An AP photo, probably of this explosion, clearly shows a veil of ash moving almost all along the SE flank. Described as an "important avalanche of ash" in the original report, it was in fact nothing but a veil of ash that moved slowly by gravity and deposited very little material. Six other explosions project ash more than 1.5 km above the summit of 30.

 

A change of wind on March 31 sends ash from the continuous explosions of the volcano on more populated areas. The ash fall started around noon in the Kelso-Longview area (75,000 inhabitants), about 65 km to the west, leaving a thin layer of light colored abrasive material. Only slight ventilation occurred during the night of March 31 to April 1; three earthquakes of M 4.5-4.7 were recorded, with foci only 1 km below the summit. The ashes of a large explosion on April 1 were collected at Spokane, 500 km east.

 

To be continued ...

 

Sources:

- USGS - Cascades Volcano Observatory - Mount St. Helens 1980

- Global Volcanism Program - St. Helens

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Publié le par Bernard Duyck
Publié dans : #Historical eruptions

Three fossilized tracks of footprints, discovered on the slopes of the Roccamonfina volcano in Campania at the end of the 18th century, have long been interpreted as the " Ciampate del Diavolo / the footprints of the Devil ". The demon came out of hell through the crater of the volcano to visit humans.

This belief lasted until the 21st century, when amateur archaeologists and then scientists became interested.

Traces of hominids in the " Devil's trails "on the Roccamonfina volcano - photo Mauro Fermariello / Science photo Library

Traces of hominids in the " Devil's trails "on the Roccamonfina volcano - photo Mauro Fermariello / Science photo Library

The human imprints have been well preserved, as they were printed in deposits of pyroclastic density current resulting from multiple collapses of a subplinian column emitted by an eruption of Roccamonfina, then covered by another pyroclastic flow. Erosion did not reveal them until the end of the 18th century.

The footprints, short and very wide (average length 24 cm and average width 10 cm), are kept on a steep slope, associated with handprints, and attributed to bipedal hominids having an autonomous process ... homo erectus or home Heidelbergensis, according to scientists of 1.5 m high.

These three tracks testify to the activities of the first known Europeans.

Roccamonfina volcano - satellite image

Roccamonfina volcano - satellite image

Distribution of ultrapotassic and related volcanic and sub-volcanic rocks in Italy and the surrounding area - (from Conticelli et al., 2007, 2010a, 2011 / Geological field trips - The Vesuvius and the other volcanoes of Central Italy - R. Avanzinelli & al .

Distribution of ultrapotassic and related volcanic and sub-volcanic rocks in Italy and the surrounding area - (from Conticelli et al., 2007, 2010a, 2011 / Geological field trips - The Vesuvius and the other volcanoes of Central Italy - R. Avanzinelli & al .

Simplified geological map of the Roccamonfin volcano. The insert shows the quaternary volcanoes of the Roman region (V: Vulsini, C: Cimini, Vi: Vico, S: Sabatini, AH: Alban Hills, E: Ernici, R: Roccamonfin, PF: Phlegrean Fields, SV: Somma Vesuvio (Modified by Giannetti and Francaviglia, 1994) - Doc. 'The Devil'sTrails' reference in sources

Simplified geological map of the Roccamonfin volcano. The insert shows the quaternary volcanoes of the Roman region (V: Vulsini, C: Cimini, Vi: Vico, S: Sabatini, AH: Alban Hills, E: Ernici, R: Roccamonfin, PF: Phlegrean Fields, SV: Somma Vesuvio (Modified by Giannetti and Francaviglia, 1994) - Doc. 'The Devil'sTrails' reference in sources

The Roccamonfina volcano belongs petrographically to the magmatic province of Campania, with the Phlegrean Fields, Vesuvius, the Pontine Islands, Ischia and Procida. This volcano represents its most northerly volcanic group.

Its basal diameter is 18-20 km., And its morphology in small caldera is marked by a sector of northern collapse.

 

Its first phase of activity between 1.54Ma and 340,000 years formed a stratocone, a collapse caldera, with between 385,000 and 335,000 years, successive deposits of important ignimbrites, called "Brown leucititic tuff ", marking the end of the first phase, with phonolitic domes.

A second phase of activity was marked by various units of pyroclastic flows: the "White trachytic tuff ", between 385,000- 335,000 years, and the "Yellow trachitic tuff ", between 327,000 and 230,000 years.

The terminal phase formed the trachybasaltic lava dome of Monte St. Croce, between 155,000 and 53,000 years ago.

Roccamonfina volcano - Foresta. View of the trampled surface with the last (distal) track segment (footprints 21-26) of track A. - Doc. 'The Devil'sTrails' reference in sources

Roccamonfina volcano - Foresta. View of the trampled surface with the last (distal) track segment (footprints 21-26) of track A. - Doc. 'The Devil'sTrails' reference in sources

The tracks are located in the non-welded pyroclastic deposits dated 385,000 - 335,000 years, rich in zeolite, and placed at a relatively low temperature (<600 ° C) and borrowed by descending hominids (traces of deep feet and hands ) on a relatively cool plastic surface, leaving their fingerprints on it.

 

Sources:

- The Devil's Trails: Middle Pleistocene Human Footprints Preserved in a Volcanoclastic Deposit of Southern Italy - Marco Avanzini & al. - Ichnos, 15: 3.179 - 189 - DOI: 10.1080 / 10420940802470458 - link

- Forestepping-backstepping stacking pattern of volcaniclastic successions: Roccamonfina volcano, Italy - D.De RitaaG.-Giordanoa-S.Millib - link

- The Vesuvius and the other volcanoes of Central Italy - R. Avanzinelli & al. - link

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Publié le par Bernard Duyck
Publié dans : #Excursions and trips, #Historical eruptions

A glance at the inhabited areas, clinging to the walls of the caldera, we discover small white volumes ... which have their roots in the cliff, in the layers of rocks or pumice emitted by volcanic eruptions.

Various conditions pushed the inhabitants to build their houses in troglodytes or semi-troglodytes. The declivity of the land, the nature of the soil, and the proximity of the materials (black rock, red rock and pumice) - without much wood - and the lack of means of transport have favored this type of habitat, named Yposkafa.

Santorini - the houses of Fira hanging on the walls of the caldera - in the background, the set of domes and lava flows of Nea Kameni - photo © Bernard Duyck 09.2019

Santorini - the houses of Fira hanging on the walls of the caldera - in the background, the set of domes and lava flows of Nea Kameni - photo © Bernard Duyck 09.2019

Santorini - Oia, some mills, and its houses with flat roofs, or semi-cylindrical or semi-spherical cupolas, separated by a few alleys on stairs - photo © Bernard Duyck 09.2019

Santorini - Oia, some mills, and its houses with flat roofs, or semi-cylindrical or semi-spherical cupolas, separated by a few alleys on stairs - photo © Bernard Duyck 09.2019

They are houses all in length, with a narrow facade. The exterior volumes are covered with flat roofs, or dome of different shapes and sizes.

The homes designed by native people meet the needs and bioclimatic requirements: the walls are thick, thermally inert, and therefore cool in summer and warm in winter; the habitat is largely buried, with a volume calculated at the fairest and at minimal openings and positioned according to the prevailing winds to ensure good ventilation, ... everything contributes to thermal comfort. The white lime paint reverberates the sun's rays.

The colors are mainly white, and blue, which symbolize Santorini.

Santorini - the Yposkafas - cut in a wall of the caldera characterizing the troglodyte dwellings dug in volcanic materials - drawing © Bernard Duyck 09.2019

Santorini - the Yposkafas - cut in a wall of the caldera characterizing the troglodyte dwellings dug in volcanic materials - drawing © Bernard Duyck 09.2019

Santorini - House in black and red volcanic stones - photo © Bernard Duyck 09.2019

Santorini - House in black and red volcanic stones - photo © Bernard Duyck 09.2019

This habitat is found in towns that are open on the caldera, Fira, Imerovigli and Oia, but also in the small fortified towns of the interior, such as Emporio, Pyrgos Callisti, and Megalochori, where a troglodyte habitat remains under a current house.

In the cellar, the house has two small vaulted rooms, with utilitarian cavities, lit by a tiny opening and the entrance door.

Santorini - Megalochori - the two rooms of a troglodyte dwelling, excavated in cellar in the pumiceous ground under the current house - photo © Bernard Duyck 09.2019
Santorini - Megalochori - the two rooms of a troglodyte dwelling, excavated in cellar in the pumiceous ground under the current house - photo © Bernard Duyck 09.2019

Santorini - Megalochori - the two rooms of a troglodyte dwelling, excavated in cellar in the pumiceous ground under the current house - photo © Bernard Duyck 09.2019

Santorini - Pyrgos Callisti - White houses with blue doors in alleys where it is good to get lost - photo © Bernard Duyck 09.2019

Santorini - Pyrgos Callisti - White houses with blue doors in alleys where it is good to get lost - photo © Bernard Duyck 09.2019

Other typical structures complete the architecture, many small churches with colorful dome, mills, now converted into rent, and Kapetanospita, Captains' houses on the upper and more spacious neighborhoods, neoclastic 19 ° century favorable to the navy.

Santorini - Oia - ruins of a neoclassical red lava stone house, plastered on the ground floor - Photo © Bernard Duyck 09.2019

Santorini - Oia - ruins of a neoclassical red lava stone house, plastered on the ground floor - Photo © Bernard Duyck 09.2019

Santorini - Pyrgos - church and its cemetery, overlooking the caldera - photo © Bernard Duyck 09.2019

Santorini - Pyrgos - church and its cemetery, overlooking the caldera - photo © Bernard Duyck 09.2019

Sources:

- Petit Futé, Santorini guide

- Ankyra - Travel, architecture and other discoveries - Santorini - link

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Publié le par Bernard Duyck
Publié dans : #Excursions and trips, #Historical eruptions

Historical volcanism has today created two islands in the center of the caldera, Palea Kameni and Nea Kameni.

Their construction probably began shortly after the Minoan eruption; they are the subaerial expression of activity, with the summit 500 meters above the calderal floor. The pyroclastic cone broke through the water level in 197 BC, and the last eruption of Nea Kameni dates back to 1950.

The vents are located on a NE-SW tectonic line, which controls the regional rise of magma : the Kameni line.

Santorini - Nea Kameni, in the center of the caldera, seen from Fira - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni, in the center of the caldera, seen from Fira - photo © Bernard Duyck 09.2019

Santorini - bathymetric / topographic section N-S of the island - Doc.G.E.Vougioukalakis 2003

Santorini - bathymetric / topographic section N-S of the island - Doc.G.E.Vougioukalakis 2003

The evolution of these islands was made during nine subaerial eruptions, whose products are all of dacitic nature: domes, lava flows channeled or with levees, block lava flows, plumes of ash, ballistic products.
Bathymetric data reveal subaqueous / lava flows in cushions, which makes the total issued at 4.85 +/- 0.7 km³.

In the diagram below, the location and the flows cast.
Thumbnail n ° 1: 197 BC - formation of the Iera pyroclastic cone
Thumbnails 2-3 about Palea Kameni, with:
- 46-47 AD - extrusive activity and formation of Palea Kameni
- 726 AD - explosive activity in the northern part of Palea Kameni, responsible for a lava lobe in blocks near Agios Nikolaos.

Santorini - historical eruptions - photo document © Bernard Duyck 09.2019

Santorini - historical eruptions - photo document © Bernard Duyck 09.2019

 Santorini - Palea Kammeni, seen from Nea Kameni - photo © Bernard Duyck 09.2019

 Santorini - Palea Kammeni, seen from Nea Kameni - photo © Bernard Duyck 09.2019

Santorini - Lava lobe in blocks on Palea Kammeni, near Aghios Nicholaos church - photo © Bernard Duyck 09.2019

Santorini - Lava lobe in blocks on Palea Kammeni, near Aghios Nicholaos church - photo © Bernard Duyck 09.2019

Santorini - arrival on Nea Kameni between the lava flows - photo © Bernard Duyck 09.2019

Santorini - arrival on Nea Kameni between the lava flows - photo © Bernard Duyck 09.2019

The activity of Nea Kameini ranges from 1570 to 1950:

- 1570 - (1573): extrusion of the lava dome Mikri Kameni

- 1707 -1711: effusive / explosive eruptions forming the northwestern part of Nea Kameni

- 1866 - 1870: effusive activity concerning the south of Nea Kameni

- 1925 - 1928: extrusion of domes Daphne and Nautilus and castings, explosions at the summit crater and plumes of ash. Growth to the north and east fills the bay between Mikri and Nea Kameni. A plume linked to phreatomagmatic activity rises to 3,300 meters, then the activity becomes phreatic.

Nea Kameini 1950 - photo Greece.is


- 1939-1941: Extrusion of the Triton, Ktenas, Fouqué, Smith-Reck, and Niki domes, and lava flows, summit explosions and ash plumes. Typically phreatic explosions precede lava extrusion.

- 1950: extrusion of the small dome Liatsikas preceded by phreatic explosions. The activity lasted a month.

Santorini -Nea Kameni - lava flows of 1939-1941 - Doc. G.E. Vougioukalakis / 2005

Santorini -Nea Kameni - lava flows of 1939-1941 - Doc. G.E. Vougioukalakis / 2005

Santorini - Nea Kameni - lava flow in blocks seen from the caldera - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - lava flow in blocks seen from the caldera - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - a set of domes and lava flows - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - a set of domes and lava flows - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - the summit craters - photo © Bernard Duyck 09.2019
Santorini - Nea Kameni - the summit craters - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - the summit craters - photo © Bernard Duyck 09.2019

In 2011-2012, a phase of instability marked the caldera, with numerous small volcano-tectonic earthquakes of M <3.3 at a depth of 1-6 km on an almost vertical plane of 6 km in length on the Kameni line, accompanied by inflation of up to ten cm. , which probably corresponds to an intrusion of 10-20 million cubic meters under the caldera at 3-6 km depth (magmatic, magma + fluids, or tectonics origin ?).

The present activity is fumarolic and marks the twin summit craters, and hot springs, with green waters (due to the presence of Fe 2+ / colloidal pyrite, and redheads (near-surface oxidation to Fe 3+).
 

Santorini - possible sources and transfer of magmatic  CO2 and He into the caldera - Doc. Moreira & al. 05

Santorini - possible sources and transfer of magmatic CO2 and He into the caldera - Doc. Moreira & al. 05

Santorini - Nea Kameni - fumarolic sulfur vent - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - fumarolic sulfur vent - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - bathing activity in the waters of hot springs - photo © Bernard Duyck 09.2019

Santorini - Nea Kameni - bathing activity in the waters of hot springs - photo © Bernard Duyck 09.2019

Sources:

The morphodynamic evolution of Santorini volcanic complex - 09,2019 - Paraskevi Nomikou, Konstantinos Vouvalidis and Spyros Pavlides

Geological Society memoir n ° 19 Santorini volcano - T.H.Druitt & al.1999

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Santorini - current distribution of Skaros lavas and Therasia dome complex - Doc. Druitt & al. 1999

Santorini - current distribution of Skaros lavas and Therasia dome complex - Doc. Druitt & al. 1999

A little jumpto north of Santorini, towards the Skaros Shield and the Therasia Dome Complex.
 

The Skaros Shield was built inside the Caldeira generated by Middle tuff eruptions (70,000 - 54,000 years ago) and covered it. The remains of the shield can be seen in Cape Tourlos (on Thêra) and on the island of Therasia.

The remains at Cap Tourlos consist of a basal complex of domes and dacitic flows, surmounted by a sequence 300 meters thick of basalts and andesites, and capped by a welded spatter agglomerate of Upper Scoriae 2, resulting from the of the development of the Skaros Shield and an explosive andesitic eruption.

Cape Tourlos, seen from the caldera - we can distinguish the succession of dacitic flows, the thickness of basalts and andesites, capped by a welded spatter agglomerate of Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cape Tourlos, seen from the caldera - we can distinguish the succession of dacitic flows, the thickness of basalts and andesites, capped by a welded spatter agglomerate of Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019
Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Cap Tourlos, formed from the remains of the Skaros Shield, seen from the village of Imerovigli on Thêra - The upper part consists of a welded spatter agglomerate of the Upper Scoriae 2 - photo © Bernard Duyck 09.2019

Following the Upper Scoriae 2 episode, the extrusion of rhyodacites from many vents constructed the lava domes complex on the western flank of Skaros. The remains dominate the walls of the current caldera in Therasia, in a succession of more than 200 meters thick.

Thin flows of weakly phyric andesite to Oia (Oia andesites, etc.) occupy the same stratigraphic level and were probably erupted by mouths on the flank of the Skaros Shield.

Santorini - Therasia, view from Nea Kameini in the center of the caldera - - photo © Bernard Duyck 09.2019

Santorini - Therasia, view from Nea Kameini in the center of the caldera - - photo © Bernard Duyck 09.2019

Santorini - Therasia - rhyodacites surmounting the ancient western flank of the Skaros Shield - photo © Bernard Duyck 09.2019

Santorini - Therasia - rhyodacites surmounting the ancient western flank of the Skaros Shield - photo © Bernard Duyck 09.2019

Santorini - Therasia, the lavas of the northern tip - photo © Bernard Duyck 09.2019

Santorini - Therasia, the lavas of the northern tip - photo © Bernard Duyck 09.2019

The so called Cape Riva eruption occurred 21,000 - 18,000 years ago; Its products are largely dacitic or rhyodacitic, and chemically resemble to the lavas of the Therasia dome complex.

The initial phase was Pliny, with falls and deposits of pumice preserving much of the walls of the northern caldera.

The collapse of the Plinian column occurred at the end of eruption, and produced a distinctive red-brown weld ingnimbrite. The eruption then became more violent with discharge of pyroclastic flows and unfused ignimbrite. It ended with the installation of a second welded ignimbrite on the north of Thêra.

A distal distribution of tephra on the eastern Mediterranean, towards Lesbos and the Sea of ​​Marmara, is recognized as a y-2 bed of marine ash.

Morphological evolution of Santorini between 70 and 21 ka - according to Druitt & al. 1999 / via Evi Nomikou

Morphological evolution of Santorini between 70 and 21 ka - according to Druitt & al. 1999 / via Evi Nomikou

Santorini - the walls of the caldera under Oia - photo © Bernard Duyck 09.2019

Santorini - the walls of the caldera under Oia - photo © Bernard Duyck 09.2019

Santorini - the red ignimbrites of the Cape Riva eruption - photo © Bernard Duyck 09.2019

Santorini - the red ignimbrites of the Cape Riva eruption - photo © Bernard Duyck 09.2019

Let's go back to Cap Tourlos, which has been inhabited since 1207, after the integration of the island into the Venetian Duchy of the Aegean Sea. The natural rock fortress was chosen as the seat of the capital, and numerous seigniorial and religious buildings were built there. In 1480, the island gave to Pizanias Domenico, son of the Duke of Crete as dowry for his marriage to Princess Fiorentza, daughter of the Duke of Naxos. One hundred years later, the Duchy of the Aegean Sea passed into the hands of the Ottoman Empire.

Thomas Hope describes the colony, in his book "Images of the 18th Century", as a fortress to defend itself from pirate raids; A continuous facade of houses with a few small openings protected the village from the only possible access to the east, and doors accessed by a movable wooden bridge, could close in the event of a hostile invasion.

An earthquake in 1650 caused terrible damage, after which the inhabitants abandoned this narrow and difficult environment for Fira. The move was not final until the last decades of the 18th century, due to the continuing pirate raids.

Santorini - Cap Tourlos - drawing from the Thomas Hope Collection (Benaki Museum) and its interpretation - the current photo of the site is located higher in the article - Doc. Santorini.net - one click to enlarge

Santorini - Cap Tourlos - drawing from the Thomas Hope Collection (Benaki Museum) and its interpretation - the current photo of the site is located higher in the article - Doc. Santorini.net - one click to enlarge

Sources:

- The morphodynamic evolution of Santorini volcanic complex - 09,2019 - Paraskevi Nomikou, Konstantinos Vouvalidis and Spyros Pavlides

- Geological Society memoir n ° 19 Santorini volcano - T.H.Druitt & al.1999

- Santorini.net - Skaros, the capital of Thêra under the Venetian occupation - by Clairy Palyvou, architect, professor emeritus of the Aristotle University of Thessaloniki

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Publié dans : #Excursions and trips, #Historical eruptions
Santorini - archaeological site of Akrotiri - xeste 2 / facade north - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - xeste 2 / facade north - photo © Bernard Duyck 09.2019

Excavations still in progress at Akrotiri have yielded many finds, the study of which has challenged ancient theories about the history of the Aegean Sea.

The site of Akrotiri has been inhabited since the middle of the 5th millennium BC; At the end of the third millennium and the beginning of the second millennium BC, Akrotiri was an important commercial and urban center of cosmopolitan character, with a sophisticated culture.

Specialization in the fields of craftsmanship and the division of labor is reflected in the products of this culture: pottery, metalworking, shipbuilding, etc., and testifies to the urban character of the Santorini society.

Santorini - archaeological site of Akrotiri - stratification of ash and pumice deposits - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - stratification of ash and pumice deposits - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - Shop with "pithois" (large storage jars) - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - Shop with "pithois" (large storage jars) - photo © Bernard Duyck 09.2019

The houses have two to three floors and many rooms. The most luxurious were built with carved stones (they are called "xestes"), the most modest in mud and straw. Wooden beams support the ceilings and lintels of doors and windows; they were equipped with sanitary facilities, household equipment and furniture, of which casts were found in the ashes.

The houses are nested in an urbanized plan equipped with a network of sewers, and are divided in small streets which widen in places of variable size in places.

 

Map of Akrotiri at the Bronze Age around 1600 BC - Doc.Maximilian Dörrbecker / Kimdime69

Map of Akrotiri at the Bronze Age around 1600 BC - Doc.Maximilian Dörrbecker / Kimdime69

Santorini - archaeological site of Akrotiri - digital reconstruction of a two-storey house and a decorated interior, with doors and cupboards, and paved with volcanic stone slabs - photo © Bernard Duyck 09.2019 - one click to enlarge
Santorini - archaeological site of Akrotiri - digital reconstruction of a two-storey house and a decorated interior, with doors and cupboards, and paved with volcanic stone slabs - photo © Bernard Duyck 09.2019 - one click to enlarge

Santorini - archaeological site of Akrotiri - digital reconstruction of a two-storey house and a decorated interior, with doors and cupboards, and paved with volcanic stone slabs - photo © Bernard Duyck 09.2019 - one click to enlarge

The murals found in the ruins testify to the daily life of the activities and the appearance of the inhabitants of Akrotiri, merchants, sailors or craftsmen; The nature scenes show the original links with Greece, and the contacts with Egypt. They are all true works of art, which will be mentioned in an article on art.

Wool or linen tissues were dyed naturally, and sometimes expensive products: murex shells were found, and saffron was grown.

Santorini - archaeological site of Akrotiri - West house / room 4 - decoration with a young man with fish, naked and shaved head - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - West house / room 4 - decoration with a young man with fish, naked and shaved head - photo © Bernard Duyck 09.2019

The great eruption of 1600 BC covered this civilization with pumice and ashes, apparently without much casualties ... only pottery and some inexpensive utensils, no skeletons (as in Pompeii and Herculaneum the eruption of Vesuvius). The inhabitants of the island, populated at the time, were able to assess the risks and flee, with their valuables, from the first strong earthquakes ( traces visible on a staircase), or eruptive manifestations, thanks to their fleet.

Santorini - archaeological site of Akrotiri - broken stairs in the delta complex of excavations - photo © Bernard Duyck 09.2019

Santorini - archaeological site of Akrotiri - broken stairs in the delta complex of excavations - photo © Bernard Duyck 09.2019

Source : Akrotiri - Thera and the Mediterranean - by Nanno Marinatos / Edit. Militos

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Santorini - pumice deposits above the port of Athinios - photo © Bernard Duyck 09.2019

Santorini - pumice deposits above the port of Athinios - photo © Bernard Duyck 09.2019

The eruption of Santorini at the end of the Bronze Age, also called the Minoan eruption because it may have influenced the decline of the Minoan Civilization, is both an event marking volcanology and archeology.

 

The last Plinian eruption of Santorini emitted between 30 and 80 km³ (equivalent in dense rocks) of rhyodactic magma, largely in the form of pyroclastic flows, deposits preserved as ignimbrites in the different surrounding submarine basins.

The eruption impacted the Mediterranean world from the end of the Bronze Age through a combination of ashfall, climate change and tsunamis.

 

Its dating : the last dating was done by the method 14C on a piece of olive wood buried in the deposits of the eruption (Friedrich & al., 2006 - reliability 95%).

The dead insects found refine the month of eruption in June - early July (Panagiotakopulu & al 2013)

Santorini - Friedrich showing the place of discovery of the olive wood in the pumice wall phase P1 of the Minoan eruption - Doc. Science AAAS

Santorini - Friedrich showing the place of discovery of the olive wood in the pumice wall phase P1 of the Minoan eruption - Doc. Science AAAS

Santorini - pumice deposits above the cliffs of the caldera, internal side - photo © Bernard Duyck 09.2019

Santorini - pumice deposits above the cliffs of the caldera, internal side - photo © Bernard Duyck 09.2019

Its course :

According to many volcanological studies, there is a consensus that it has taken place in four major phases (P1 to P4), and a precursory initial phase (P0).

 

- Phase 0, based on a layer of 10 cm. between the pre-Minoan deposits and those of phase 1, consisting of two layers of lapilli and ash, corresponds to explosions and a subplinian plume 7-10 km in height.

- Phase 1, the first phase of the Plinian eruption, generated a plume of height estimated at 36 +/- 5 km.and produces deposits of pumice between 10 cm. and 6 meters thick on Thêra, Therasia and Apronisi.

- Phase 2 is marked by violent phreatomagmatic explosions, caused by contact between marine waters and magma; base surges were generated, which produced startified deposits of more than 12 cm. Thick. (analysis of P2 and P3 deposits in the Mavromatis quarry)

- During phase 3, the increase in the water-magma ratio produced dense, moist, low temperature pyroclastic flows with a transition to muddy flows.

Collapses of the eruptive column produced the largest unit, in the form of massive ignimbrite, thick up to 55 meters in the field, and composed of multiple units and created a cone of tuff, which filled the existing caldera.

- Phase 4 saw the production of high-temperature pyroclastic flows (300-500 ° C), which formed fine-grained, non-welded ignimbrites around the caldera and on the costal plains.

The dominant facies is brownish to pink ignimbrite, called "tan-ignimbrite", which may be contemporaneous with the major collapse of the caldera. A cliff of this ignimbrite "tan" of 40 meters high borders the beach of Vlychada south of Akrotiri.

 

- At the end of the eruption, the caldera was dry and isolated from the sea, probably due to eruptive tufa accumulation. The multi-day flooding of the caldera began on the northwestern side following sea erosion associated with landslides.

Regional tsunamis have been generated by the flooding of P3 and P4 pyroclastic flows, possibly augmented by the mass collapse of pyroclastic deposits rapidly deposited on the slopes of the island's volcano, facing the sea. (Nomikou & al.2016)

Summary of the development of the Santorini caldera before, during and after the eruption of the LBA. (Late Bronze age) - Doc. E.Nomikou & al 2016

Summary of the development of the Santorini caldera before, during and after the eruption of the LBA. (Late Bronze age) - Doc. E.Nomikou & al 2016

Santorini - "Tan ignimbrite" of the southern area of ​​Akrotir, Vlychada beach - photo © Bernard Duyck 09.2019

Santorini - "Tan ignimbrite" of the southern area of ​​Akrotir, Vlychada beach - photo © Bernard Duyck 09.2019

Santotin - detail on the ignimbrites of Vlychada - photo © Bernard Duyck 09.2019

Santotin - detail on the ignimbrites of Vlychada - photo © Bernard Duyck 09.2019

Discovery of prehistoric structures :

The construction of the Suez Canal in 1856, linking the Mediterranean Sea and the Red Sea, required materials such as pumice, which was used in the composition of concrete.

Quarries opened on Santorini, and allowed to discover prehistoric structures, first on Therasia, analyzed by F.Lenormant in 1865, then on Thêra, where the French geologist Ferdinand Fouqué made a major discovery near Akrotiri in 1867.

The excavations, interrupted by the Franco-Prussian War of 1870, really resumed in 1967, under the direction of the Greek archaeologist Spyridon Marinatos, who attributed the decline of the Minoan civilization to the eruption of Santorini.

The site of Akrotiri has been inhabited since the middle of the 5th millennium BC; at the end of the third millennium and the beginning of the second millennium BC, Akrotiri was an important commercial and urban center of cosmopolitan character, with sophisticated culture.

Akrotiri - model of the excavation site - photo © Bernard Duyck 09.2019

Akrotiri - model of the excavation site - photo © Bernard Duyck 09.2019

To follow: the discovery of the excavation site of Akrotiri

 

Sources:

- The morphodynamic evolution of Santorini volcanic complex - 09,2019 - Paraskevi Nomikou, Konstantinos Vouvalidis and Spyros Pavlides

- Geological Society memoir n ° 19 Santorini volcano - T.H.Druitt & al.1999

- Akrotiri - Thera and the Mediterranean - by Nanno Marinatos / Edit. Militos

- Santorini Eruption Radiocarbon Dated at 1627-1600 B.C. by Walter L. Friedrich, Bernd Kromer, Michael Friedrich, Jan Heinemeier, Tom Pfeiffer, and Sahra Talamo - Science, 28 April 2006


- Santorini Eruption Radiocarbon Dated at 1627-1600 B.C.
https://science.sciencemag.org/content/sci/suppl/2006/04/25/312.5773.548.DC1/Friedrich.SOM.pdf

note in Volcanodiscovery by Tom Pfeiffer https://www.volcanodiscovery.com/en/santorini/minoan_eruption/1613bc_olive-tree-date.html

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