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Earth of fire

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

Articles avec #excursions and trips catégorie

Publié le par Bernard Duyck
Publié dans : #Volcanic news, #Excursions and trips

In Yellowstone National Park, the "Old Faithful" geyser in the Upper Geyser Basin received its unique name in the 19th century due to the regularity and predictability of its eruptions.

 "Old Faithful" to the max. of its activity - photo archives © Bernard Duyck 2009

"Old Faithful" to the max. of its activity - photo archives © Bernard Duyck 2009

A sample of mineralized (silicified) wood was discovered in his mouth, as evidenced by a Journal published over 60 years ago. Its radiocarbon dating has just been confirmed in a study that was just published in October 2020, on 41 dates: 1233-1362 CE.

This date corresponds to a series of severe regional droughts, which lasted for many decades, at the end of the Middle Ages climate anomaly, before the onset of the Little Ice Age.

Murray pines (Lodgepole pine) were able to thrive in the mouth of an active natural geyser only during a period of great drought that affected much of the United States, and affected the native cultures of Anasazi, Fremont and Lovelock . The remains of trees were then preserved by mineralization in an alkaline water rich in silica ... to reveal to us today the mysteries of the "Old Faithful".

"Old Faithful", the "Vieux fidèle" - beginning of eruption - photo archives © Bernard Duyck 2009

"Old Faithful", the "Vieux fidèle" - beginning of eruption - photo archives © Bernard Duyck 2009

"Old Faithful" - end of eruption - photo archives © Bernard Duyck 2009

"Old Faithful" - end of eruption - photo archives © Bernard Duyck 2009

Natural geysers are rare on the planet, because they require special conditions to form: heat input from active or recent magmatism, and adequate geometry of rock fractures underground to ensure episodic discharge. These parameters can change following earthquakes modifying the fractures, or by regional variations in precipitation, which feed underground reservoirs.

 

Climate change forecasts, which include regional droughts for the middle of the 21st century, suggest less frequent eruptions of these geysers, and even the end of their activity.

Happy are those who were able to see them in great shape!

 

Sources:

- USGS - Caldera chronicles - A time when Old Faithful wasn’t so faithful

- Geophysical Research letters - Yellowstone's Old Faithful Geyser Shut Down by a Severe 13th Century Drought

"Old Faithful" featured on the National Park / Limited Centennial Edition poster.

"Old Faithful" featured on the National Park / Limited Centennial Edition poster.

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Publié le par Bernard Duyck
Publié dans : #Excursions and trips
Palisade Head cliffs on Lake Superior, view northeast towards Shovel Point - photo Kablammo

Palisade Head cliffs on Lake Superior, view northeast towards Shovel Point - photo Kablammo

In the state of Minnesota in the United States, on the north shore of Lake Superior, stand cliffs 90 meters high whose geology is linked to volcanism: Palisade Head and Shovel Point.

 

This rock formation is part of the MRS, the Midcontinent Rift System, one of the largest continental rifts in the world.

1,100 million years old, it stretches from Kansas to Michigan, and contains magmatic and hydrothermal mineral deposits.

MRS rocks are exposed at surface only in the Lake Superior region, a member of the group of five lakes located on or near the Canada-United States border. This group of freshwater lakes consists of Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario.

Geological map of the Midcontinent Rift System (the limits of the MRS: line in bold black), with intrusive units in red, sedimentary units in green, volcanic units in purple - Doc. USGS - one click to enlarge

Geological map of the Midcontinent Rift System (the limits of the MRS: line in bold black), with intrusive units in red, sedimentary units in green, volcanic units in purple - Doc. USGS - one click to enlarge

Rhyolite organs at Palisade Head - Lake Superior, North Shore volcanic group - photo James ST John / Flickr

Rhyolite organs at Palisade Head - Lake Superior, North Shore volcanic group - photo James ST John / Flickr

Detail on rhyolite organ at Palisade Head - Lake Superior, north shore volcanic group - photo James ST John / Flickr

Detail on rhyolite organ at Palisade Head - Lake Superior, north shore volcanic group - photo James ST John / Flickr

Palisade Head and Shovel Point are formed by a rhyolitic lava flow, extruded 1.1 billion years ago.

 

Regional volcanism, under the influence of molten magma rising from a deep mantle plume, has resulted in large intrusions and surface eruptions of basalt and rhyolite flows, largely confined to elongated and sagging basins formed along of the rift system, in a relatively short interval estimated at 26 million years.

At the end of the major period of volcanism, around 10 million years ago, the basalt sections in the central basins of Lake Superior had a thickness of about 20 km.

Shovel Point Sea Caves - photo SuperiorTrails

Shovel Point Sea Caves - photo SuperiorTrails

Diagram of MRS volcanism at the rift stage, 1.100Ma ago - Doc. USGS

Diagram of MRS volcanism at the rift stage, 1.100Ma ago - Doc. USGS

After this major period of volcanism and rifting, the thermal and mechanical gradient of the mantle plume began to decrease, ending crustal extension and rifting.

The SRM then underwent regional cooling and subsidence, evolving into a series of sagging basins along the central axis of the rift system. Flowing waters and glaciers eroded the highland MRS rocks along the sides of the central basins and flowed to the center of the rift where they deposited clastic sediment. These clastic sediments, such as sand, gravel, and cobbles, accumulated over millions of years, creating layers of solidified sedimentary rock, eventually reaching a thickness of about 7 kilometers (4.3 miles) near the center of the rift basins in Lake Superior.

Around 1080 Ma, compression of tectonic origin shortened the width of the fault. The compression caused the central basins to heave along the faults bordering the basins. In parts of the rift system, this reverse movement placed older basalt on top of younger sedimentary rocks ... a huge upheaval.

 

Sources:

- USGS - America's volcanic past - Minnesota

- USGS - Mineral deposits of the Midcontinent Rift System

- Department of Natural resources - Tettegouche State Park

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Publié le par Bernard Duyck
Publié dans : #Excursions and trips

The Columbretes archipelago, located in the Mediterranean between the east coast of Spain and the Balearic Islands, 30 nautical miles from Grao de Castellón, is made up of four groups of volcanic islands: La Columbrete Grande, La Ferrera, La Foradada and el Carallot.

These islands are installed on funds 80 meters deep and cover a space of three nautical miles.

 Columbretes Archipelago - the different island groups: insets on the right, top: Grande island group (or Grossa island) 14.30 ha - center: La Ferrera group 1.95 ha - La Foradada group 2.21 ha - bottom: Carallot group 0.49 ha - Doc. Parque Natural Islas Columbretes

Columbretes Archipelago - the different island groups: insets on the right, top: Grande island group (or Grossa island) 14.30 ha - center: La Ferrera group 1.95 ha - La Foradada group 2.21 ha - bottom: Carallot group 0.49 ha - Doc. Parque Natural Islas Columbretes

The name of the archipelago comes from Roman and Greek navigators, who noticed that the main island was inhabited by a large number of snakes (Colubraria, on Latin maps).

These islands were visited only by fishermen and pirates until the middle of the 19th century, and the destruction of snakes by arson.

Colonization took place between 1856 and 1860, with the construction of a lighthouse to guide boats navigating near the islands.

 

The Columbretes Islands are now part of a nature reserve, and the number of daily visitors has been limited for this reason to 78 people, who must take the guided tour in groups of 20 and at specific times.

Islas Columbretes - La Columbrete Grande - photo visitaislascolumbretes

Islas Columbretes - La Columbrete Grande - photo visitaislascolumbretes

Islas Columbretes - La Columbrete Grande - the lighthouse - photo Flickr / Manel

Islas Columbretes - La Columbrete Grande - the lighthouse - photo Flickr / Manel

The volcanic origin:

The archipelago is located in the Gulf of Valencia, which is a rift formed before the oceanic opening of the north-western Mediterranean basin during the Lower Miocene.

Volcanism corresponds to two cycles of different ages and nature:

The first, from the Upper Oligocene to the Middle Miocene, is characterized by calc-alkaline materials (rhyolites, trachytes, dacites and rhyodacites).

The second cycle is alkaline and more recent, in the Quaternary (1 to 0.3 Ma on Grossa Island).

The interest, in addition to its difficulty of access and its low attendance, is mainly petrological and geochemical. It constitutes a unique and representative example of alkaline volcanism in the western Mediterranean. Basanites and phonolites predominate, accompanied by tephrites, tracytes, syenites, and intermediate terms.

At the morphological level, the archipelago reveals volcanic stratigraphy, coastal erosion and sedimentation, forms of wind erosion, landslide marks, and craters.

 

Sources:

- Instituto Geologico y minero de Espana - Volcanismo Cuaternario de las Islas Columbretes - link

- Reservas Marinas de Espana - Islas Columbretes

- Structure and volcanism of the Valence Pit - Agnès Maillard and Alain Mauffret / 1991 / Bulletin of the Geological Society of France

- Specially protected areas in the Mediterranean - SPAMI 2010 / SP7

Islas Columbretes - Illa Foradada - photo Castellaruralhomes

Islas Columbretes - Illa Foradada - photo Castellaruralhomes

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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 : #Art on the way of fire, #Eruptions historiques, #Excursions and trips

In Akrotiri, at least one frescoed room has been found in every house. This characteristic is a testimony to the high standard of living of the inhabitants. They describe sports games or cultural scenes, or everyday life, with landscapes of Santorini or Egypt.

The execution is neat, the details are precise, the natural color spectrum extended. The paintings are started on a coating) wet lime, but finished on a dry support.

The pigments used are ocher and jarosite for yellow, ocher or hematite for red, and Egyptian blue. The contours are drawn in graphite. The colors are used in a united way, without gradients.

Akrotiri - frescoes of the House of the Ladies - Museum of Prehistory - photo © Bernard Duyck 09.2019

Akrotiri - frescoes of the House of the Ladies - Museum of Prehistory - photo © Bernard Duyck 09.2019

Akrotiri - frescoes of the Maison des Dames - detail about the clothes of a young woman, "the lady with Papyrus" - Museum of prehistory - - photo © Bernard Duyck 09.

Akrotiri - frescoes of the Maison des Dames - detail about the clothes of a young woman, "the lady with Papyrus" - Museum of prehistory - - photo © Bernard Duyck 09.

Akrotiri - frescoes of the House of the ladies - scene of offering to the mistress of house, or to the goddess - photo © Bernard Duyck 09.2019

Akrotiri - frescoes of the House of the ladies - scene of offering to the mistress of house, or to the goddess - photo © Bernard Duyck 09.2019

Frescoes found in the "House of the ladies" :

The storied house was named after the discovery of frescoes with female characters and papyrus, a motif borrowed from the Egyptian cult of the goddess Hathor.

Another fresco depicts the preparation of a ceremony by the mistress of the house; A lady wears heavy breasts, belonging, according to Marinatos, to a married matron.

These female figures, of different ages, represent a female feminine community of Akrotiri, during a ceremony of offerings to the goddess.

Women wear either a colorful skirt down to the ankles and a blouse with sleeves to the elbow, or a short-sleeved dress, low-cut well below the breasts. The clothes are woven and often adorned with bands.

Akrotiri - Xeste 3 - young girl, saffron picker in flowers - Doc. Marinatos

Akrotiri - Xeste 3 - young girl, saffron picker in flowers - Doc. Marinatos

Akrotiri - Xeste 3 - fresco of saffron pickers - Doc. Marinatos

Akrotiri - Xeste 3 - fresco of saffron pickers - Doc. Marinatos

 Akrotiri - Xeste 3 - fresco of the Mistress of animals - Doc. Marinatos

Akrotiri - Xeste 3 - fresco of the Mistress of animals - Doc. Marinatos

Frescoes of "Potnia Theron", the Mistress of animals and crocus collection in bloom.

Decorating a wall on the second floor of the house Xeste 3 / room 3, a girl, the skull partly shaved (gray head) leaving a few locks of long hair and festive clothes, picks crocus flowers on a hill.

This collection shows a significant economic activity, and the trade of saffron. This fresco represents the human level of society ... the divine level is depicted in another part of the floor, with the offering of the pistils to the great goddess, sitting on a podium and holding a winged griffin on a leash. A monkey offers him a handful of crocus, while a girl prepares another basket with flowers. No direct contact between humans and the goddess. We find monkey and griffin on murals of Knossos.

This house is considered a place of initiation and rites of passage, because of the layout of the place and the various frescoes.

Akrotiri - fresco of the blue monkeys - Museum of Prehistory - photo © Bernard Duyck 09.2019
Akrotiri - fresco of the blue monkeys - Museum of Prehistory - photo © Bernard Duyck 09.2019

Akrotiri - fresco of the blue monkeys - Museum of Prehistory - photo © Bernard Duyck 09.2019

Fresco of the room of the blue monkeys (room B6)

The theme of the fresco, which decorates the Beta room, is the celebration of nature.

In a landscape depicting the nature of Thêra -  water in the bottom, rocks, and trees - the monkeys are represented in a composition, in various poses, with an impression of movement corresponding to their natural attitude, suggesting that the painter was able to observe directly these monkeys, imported from the eastern Mediterranean.

In Knossos we find a similar fresco, proof that both islands were occupied by men and women of the Minoan civilization.

 

Sources:

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

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

The scenery planted, let's move on to the history of the volcanic field of Santorini, which consists of 6 different stages.

- Akrotiri Volcanoes (about 2 Ma - 600,000 years old)
- Ash cones of the Akrotiri peninsula (about 600 - 300 ka)
- Peristeria Volcano (530 - 300 ka)
- Products of the first eruptive cycle (360-172 ka)
- Products of the second eruptive cycle (172 ka - 1613 BC)
- Shield Kameni (1613 BC)

 

The volcanism in the Santorini region began about 2 million years ago, when the first eruptions occurred on the seabed in the region of the Akrotiri Peninsula and probably also at the location of the islands Christiania, 20 km southwest of Santorini.
The activity led to the construction of dacitic lava domes that eventually formed a series of islands, still visible in the hills of the Akrotiri Peninsula.

 In a second time, a stratovolcano (Peristeria volcano) formed in the northern part of Santorini, some parts of which are still visible in the cliffs and slopes of Mikro Profitis Ilias and Megalo Vouno.

From 400,000 years ago, volcanic activity moved to the center of the current caldera. The most characteristic type of activity over the past 400,000 years has been the cyclical construction of volcanoes-shields interrupted by major explosive and destructive events such as the Minoan eruption of about 3,600 years ago.

(Full text and details: see Druitt & al., 1999 - references in sources)

The volcanic complex of Santorini - Doc. The morphodynamic evolution of Santorini volcanic complex - Doc. Nomikou, Vouvalidis, Pavlides 2019

The volcanic complex of Santorini - Doc. The morphodynamic evolution of Santorini volcanic complex - Doc. Nomikou, Vouvalidis, Pavlides 2019

Eruptive history of Santorini - Doc. Thamsin Mather

Eruptive history of Santorini - Doc. Thamsin Mather

Santorini - Thêra - the lavas of Cap Skaros, under Imerovigli - photo © Bernard Duyck 09.2019

Santorini - Thêra - the lavas of Cap Skaros, under Imerovigli - photo © Bernard Duyck 09.2019

 Santorini - Therasia - detail of the cliffs - photo © Bernard Duyck 09.2019

Santorini - Therasia - detail of the cliffs - photo © Bernard Duyck 09.2019

The volcanic evolution of Santorini is marked by at least 4 episodes of caldera collapses that have taken place for 172,000 years, during 2 eruptive cycles, each cycle beginning with a mafic to intermediate volcanism and ending with silicic extrusions accompanied by collapse events. The remains of these are observed on the cliffs of the caldera, usually defined by unconformities and layers of underlying paleosols.

 

Caldeira 1 - 172,000 years: located south of Thêra, and defined by a discrepancy of 150 m. covered by pyroclastic deposits.

Caldeira 2 - 76,000 years old: located north of Thêra and formed by eruptive Middle tuff series, covered by lava of Skaros (67,000 years)

Caldeira 3 - 22,000 years old: located in the caldera wall north of Thêra and in the port of Fira (Minoan pumice layer of 140 m.)

Caldeira 4 - 3,600 years: located north of the Kameni line.

At the port of Athinios, we notice the collapse of the Minoan eruption (tuff) which exhumed the northwestern cliff and the shore of the pre-volcanic bedrock.

Santorini - Thêra - Cap Skaros lava - photo © Bernard Duyck 09.2019

Santorini - Thêra - Cap Skaros lava - photo © Bernard Duyck 09.2019

Santorini - Thêra - cliffs with pre-volcanic lithological basement at the port of Athinios - photo © Bernard Duyck 09.2019

Santorini - Thêra - cliffs with pre-volcanic lithological basement at the port of Athinios - photo © Bernard Duyck 09.2019

The geomorphology is revealed by an underwater topographic and bathymetric map, published by Evi Nomikou.

The walls of the caldera rise up to 300 meters above sea level, while the maximum depth of the caldera floor is about 390 meters below the water level.

Caldera de Santorini - bathymetric and topographic combined map - Doc. Nomikou & al. 2014

Caldera de Santorini - bathymetric and topographic combined map - Doc. Nomikou & al. 2014

The caldera consists of three distinct basins forming separate depositional environments.

The northern basin is the largest and deepest, between the Kameni Islands, Thirasia and the northern part of the caldera. It is connected by a narrow channel, with steep walls 300 meters deep, to an ENE-WSW structure in form of shell that lies outside the Santorini caldera, northwest of the village of Oia.

The smaller western basin, between the Islet of Apronisi, Palea Kameni and the south of Thirasia, has a depth of up to 325 meters.

The southern basin, bordered by the Kameni Islands and the southern part of the caldera, is shallower than the west basin of about 28 meters.

The morphology of the sea floor suggests that the southern basin is separated from the others by the development of a series of subaerial and submarine volcanic domes, aligned NE-SW.

 

This unique morphology plays an important role in the occurrence of rock slides and a risk of landslide over a very large area, with major risks for the internal caldera cliffs north of Thera and east of Thirasia.

 

Sources:

- The morphodynamic evolution of Santorini volcano complex - 09,2019 - Paraskevi Nomikou (National and Kapodistrian University of Athens), Konstantinos Vouvalidis and Spyros Pavlides (Aristotle University of Thessaloniki)


- Geological Society memoir n ° 19 - Santorini volcano - T.H.Druitt (Laboratory Magmas and Volcanoes (UMR6524 and CNRS), Blaise Pascal University, 5, Rue Kessler, 63038 Clermont Ferrand, France) & al.1999

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