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Earth of fire

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

excursions et voyages

Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Lassen Volcanic Center - Bumpass Hell hydrothermal area, vizw from the eastern approach trail - NPS Photo

Lassen Volcanic Center - Bumpass Hell hydrothermal area, vizw from the eastern approach trail - NPS Photo

A hundred years after the last eruption of Lassen Peak, the area remains volcanologically active  .

Safety hazards:

Different problems can accompany a future eruption at Lassen volcanic center. Where and when, are the only non- predictable data !

Most likely for the USGS will be an effusive eruption , accompanied by lava fountains and the building of a cinder cone around the vent and lava flows impacting large areas.

An explosive eruption is also possible on Lassen Peak and Chaos Crags.

The monitoring network pf CalVO is operational , and increasing of the seismicity and z deformation will prevent a future eruption . A map of areas at risk has been established, with potentially affected by pyroclastic flows and lahars areas. Areas of ash fall will depend on the prevailing winds at the time of the event.

Map of volcanic hazards - doc . USGS - Blue Points: essentially basaltic vents - triangles : mainly dacitic vents . Dotted red : max extension of pyroclastic flows - in pale buff : risk zone of lava flows - dark chamois risk zone of ash fall - orange: cumulative risk area - Pink : drainage may be affected by lahars .

Map of volcanic hazards - doc . USGS - Blue Points: essentially basaltic vents - triangles : mainly dacitic vents . Dotted red : max extension of pyroclastic flows - in pale buff : risk zone of lava flows - dark chamois risk zone of ash fall - orange: cumulative risk area - Pink : drainage may be affected by lahars .

Current hydrothermal activity :

Unique example of this hydrothermal structures in the Cascade Range, these pools of boiling mud , these noisy fumaroles , and a steaming ground  leaving sulphide gas escape, remind the potential volcanic activity of Lassen volcanic center .

Zones of hydrothermal activity include Bumpas Hell , Little Hot Springs Valley, Pilot Pinnacle , Sulphur Works, Devils Kitchen , Boiling Springs Lake and Terminal Geyser .

Bumpass Hell is one of the hydrothermal area where there are as many different structures : hot springs, fumaroles and mud pots . This area owes its name to a cowboy who worked there in the 1860s , Kendall Vanhook Bumpass : he was severely scalded when his leg went through a thin crust covering a pool of mud. He spoke about him , describing the area as " a hell ." A journalist interested in this story, convinces him to take on the spot ... that was Bumpass , but he passed through a crust covering a mud pot, and this time be amputated.

 Lassen Volcanic Center - Bumpass Hell - a pool of boiling mud - photo Randy McNally

Lassen Volcanic Center - Bumpass Hell - a pool of boiling mud - photo Randy McNally

 The danger in these hydrothermal areas is not to be overlooked ... stay on the trails and boardwalks - photo John Poimiroo - Lassen Park Foundation

The danger in these hydrothermal areas is not to be overlooked ... stay on the trails and boardwalks - photo John Poimiroo - Lassen Park Foundation

Devils Kitchen : The hot springs are so acidic that they have dug holes and wells in the bedrock, reminiscent of a devil's kitchen .

Boiling Springs Lake : It's not only a big lake of hot water ... hot springs, fumaroles and mudpots are present on its western shore. This area a little away was not developed with boardwalk and road signs ... and let see the thermal structures in their natural beauty.

Cold Boiling Lake : As its name suggests, this source is not hot , but just outside the thermal system , lively by bubbles degassing
... CO2

 

Lassen Volcanic Center - Boiling springs lake - photo NPS

Lassen Volcanic Center - Boiling springs lake - photo NPS

Lassen Volcanic Center - Sulphur Works - photo NPS

Lassen Volcanic Center - Sulphur Works - photo NPS

Lassen Volcanic Center - Little Hot Springs Valley - photo Skeptikal raptor

Lassen Volcanic Center - Little Hot Springs Valley - photo Skeptikal raptor

Lassen Volcanic Center - Cold Boiling Lake - photo NPS / Sandra Ocks

Lassen Volcanic Center - Cold Boiling Lake - photo NPS / Sandra Ocks

Terminal Geyser is not a geyser,strictly speaking ; it results from a cold flow passing over a steam vent .

 Lassen Volcanic NP - Terminal Geyser - photo Russell Virgilio / NPS

Lassen Volcanic NP - Terminal Geyser - photo Russell Virgilio / NPS

Flow Diagram of the hydrothermal system :

Rainwater and snowmelt enter the ground through permeable rock or rock fractures and faults. They are heated at depth by conduction, by a magma body or solid but hot rocks , located 8-10 km. under the Lassen Peak. This is where they charge in hydrochloric acid , sulfur dioxide and other volatiles emitted by magma or hot rock. In climbing , this acidic water will react with the rocks that surround and enriched in silica and metals.                     It will saturate the permeable rocks and accumulate in a deep reservoir called zone dominated by the liquid phase
(liquid-dominated zone); the temperature should be around 240 ° C. The waters come into boiling  when the pressure drops to a depth of about 1 km. The steam drives the water mass , and the dissolved gases , CO2 , H2S, hydrogen, nitrogen and helium to the surface ... the subsurface area, where predominate gas and steam, is named dominated by the steam phase ( vapor-dominated area )
 

The Lassen hydrothermal system - different areas - doc . U.S. Geological Survey Fact Sheet 101-02 -  In the inset, Morgan hot springs, a hot spring.

The Lassen hydrothermal system - different areas - doc . U.S. Geological Survey Fact Sheet 101-02 - In the inset, Morgan hot springs, a hot spring.

Sources :

- USGS / CVO - Hydrothermal activity - link

- Nice pictures on this sites :

  * Hot & smelly at Lassen - link

  * Travelogue of Sing H. Lin, Ph.D / Tour of Northern California and Southern Oregon -link

- USGS - "Hot water" in Lassen Volcanic Nationa Park - by M.Clynne & al.

- National Park Service - Lassen Volcanic National Park - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

The Lassen volcanic center , located in Northern California , is composed of various volcanic units, centered on the Lassen Peak, the eruptive center with the most recent activity in the southern Cascade Range , the last eruption dates back to 1914 - 1917.

Southwest of Lassen Peak, the Mount Tehama remains, with Brokeoff Mountain , Mount Diller, Pilot Pinnacle, and Mount Conard .

Northeast of Lassen Peak , small shield volcanoes and large andesitic lava flows, with the Cinder Cone complex .

Lassen Peak, a lava dome , rises to 3,187 meters , dominating a field of dacitic domes, among which there Bumpass Mountain, Mount Helen , Ski Heil Peak, Reading Peak, Chaos Crags.

Panorama from Sunrise Peak towards the Lassen Peak - photo Patrick Muffler / USGS

Panorama from Sunrise Peak towards the Lassen Peak - photo Patrick Muffler / USGS

Lassen Volcanic National Park - the different structures or volcanic remnants - dotted : contours of Brokeoff volcano / Tehama volc . - Red , hydrothermal areas . - USGS Map

Lassen Volcanic National Park - the different structures or volcanic remnants - dotted : contours of Brokeoff volcano / Tehama volc . - Red , hydrothermal areas . - USGS Map

Ancestral activity :

There are 825,000 years, the volcanic activity began with eruptions of Rockland caldera complex . Domes of dacite to rhyolite, and lava flows are dated between 825 and 609 ka . Their extrusion culminates with an explosive eruption producing the Rockland tephra  610,000 years ago.

After the explosion and the emission of Rockland tephra (about 600,000 years ), its caldera filled with activity that forms Mount Tehama ( also referred as Brokeoff volcano - not to be confused with his remains , Broekeoff Mountain ) .

According to the stratigraphy , we note for its construction two depositional sequences ( Clynne & Muffler / USGS )

- The Mill Canyon sequence consists of a dozen flows of  basalto - andesitic to dacitic lava , of small volumes, interspersed with layers of deposits of explosive eruptions . This activity is dated to 590,000 to 470,000 years.

- The Diller sequence consists mainly of six lava flows , thick and of large-volume , lithologically similar , and issued by vents flanks between 470,000 and 385,000 years.

Brokeoff Mountain, a remnant of the Tehama / Brokeoff volcano - photo Summitpost

Brokeoff Mountain, a remnant of the Tehama / Brokeoff volcano - photo Summitpost

The " broken" part of Brokeoff Mountain - photo Urban

The " broken" part of Brokeoff Mountain - photo Urban

The remains of Tehama : from left to right , Brokeof Mt, Mt Driller and Eagle Peak

The remains of Tehama : from left to right , Brokeof Mt, Mt Driller and Eagle Peak

Mount Tehama had significant measurements : 80 km ³, for a greater height than the current Lassen Peak,  peaking before at about 3,350 meters. Can realize its occupation on the ground by connecting its remains : Brokeoff Mountain , Mount Diller, Pilot Pinnacle, and Mount Conard .

Its main vent was probably the place where now stands the Sulphur Works hydrothermal area (CVO ) .

  Explanatory panel Brokeoff volcano - linking structures visible today, we can get an idea of the stratovolcano Tehama - Lassen Volcanic Photo Nat.Park

Explanatory panel Brokeoff volcano - linking structures visible today, we can get an idea of the stratovolcano Tehama - Lassen Volcanic Photo Nat.Park

Lassen Volcanic NP - Sulphur Works hydrothermal area - photo Daniel Mayer

Lassen Volcanic NP - Sulphur Works hydrothermal area - photo Daniel Mayer

Between 385,000 and 315,000 years , a dramatic change of the volcanic activity brought down the stratocône giving birth to a breached caldera.

Various storylines attempt to explain the current topography, the truth from a mixture of three assumptions:

- Its breached caldera did not allow the installation of a lake, as was the case in Mazama , home , after its collapse , of Crater Lake. (Brochure of Lassen Volcanic National Park)

- A glacial erosion have caused the disappearance of the traces of the old caldera, in the same way as those of Mount Maidu, older ( according JPSchaeffer / Lassen Volcanic NP & vicinity . )

- After the growth of Mount Maidu , its eruption followed by its collapse , Mount Tehama fell into place , before being heavily eroded , leaving only Brokeoff mountain and Mount Diller ( St.Harris / Fire mountains of the West )

 

Next: eruptive history of Lassen dome field

Map of Lassen Volcanic National Park - doc . USGS

Map of Lassen Volcanic National Park - doc . USGS

NB: both different and  grouping the same structures , it is necessary to distinguish the Lassen Volcanic Center, engaged in Geology / Volcanology , and Lassen Volcanic National Park.

The latter was established in August 1916. Takes its name , as Lassen Peak, from Peter Lassen, one of the first white settlers in the northern Sacramento Valley , who discovered a route through the mountains , known as the Lassen Trail.

Lassen Volcanic National Park poster, illustrated by a drawing of the eruption of 1914-1917 - Original 1938 / Library of Congress .

Lassen Volcanic National Park poster, illustrated by a drawing of the eruption of 1914-1917 - Original 1938 / Library of Congress .

Sources :

- Global Volcanism Program - Lassen Volcanic Center - link

- USGS - Lassen Volcanic Center - link

- National Park Service - Lassen Volcanic National Park - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

South American obsidian sources:

In Colombia, Ingeominas reports of obsidian in a Cerro Azafatudo flow, to Cargachiquito , but the quality of the glass was not satisfactory for the operation prehistoric .

Nodules were found in ignimbritic deposits intersected by the rivers Hondo and Negro, from eruption of Huila and Cauca , dating from 4.27 to 3.46 Ma

The traces of the first occupants of the South American continent , mainly in the Andes, are found in the central Sierra of Ecuador: scrapers, arrows and obsidian blades testify to continuous human occupation for 5,000 years

Mullumica casting , consisting of two superimposed effusions , is 6 km long , for the lower effusion , and has a thickness of 150 m . It is dated from 180,000 to 200,000 years. Obsidian has been exploited during prehistory, with workshops at the foot cliff, in shelters or caves in the lava flow .

In Cotopaxi , obsidian is found in deposits from two main phases of activity, dated of the paleo- Cotopaxi , between 540,000 and 560,000 years old, and another phase, between 310,000 and 18,000 years.

 Sources of obsidian in Peru - doc . Andean Obsidian Distributions through Time

Sources of obsidian in Peru - doc . Andean Obsidian Distributions through Time

In Peru , a type of obsidian, known in the '70s as the type Titicaca Basin , and widespread in the prehispanic Andes, has its geological source in the Colca Valley near Araquipa . Geochemical types was documented under the names of Chivay Source and Cotallalli source.

Obsidian flows are still being issued , such as the eruption of the Puyehue -Cordon Caulle in 2011-2012 , in Chile.

Obsidian lava emitted by the Puyehue -Cordon Caulle volcano , Chile - 2011 Nasa Image

Obsidian lava emitted by the Puyehue -Cordon Caulle volcano , Chile - 2011 Nasa Image

"Ruta Qhapaq Ñan, El camino que nos une" - photo La Republica Peru

"Ruta Qhapaq Ñan, El camino que nos une" - photo La Republica Peru

Roads of obsidian on the South American continent :

Trade routes borrow various roads , by sea along the western coast of the continent, or on the land between the coast and the Andes on the one hand , or the heights thereof . Evidence of use indicate attendance since 10,000 years by prehistoric hunter-gatherers ( 9,000 BC to 400 AD ) , then by the Inca Empire ( Caminos del Inca) .

Movement of goods in these huge distances do not necessarily imply the movement of people on the whole journey . The product, which obsidian, can pass from hand to hand .

Under the Wari Empire (600-1100) , a leading network of communication channels have been built ( Lumbreras , 2004). The Incas inherited the territorial network to build , consolidate and organize an original centralized communication system , having own infrastructure. The extension of the network path followed that of the Inca empire in the Andes.

The Qhapaq Nan ( Quechua name meaning "the royal road" and frequently replaced by the term " Inca Trail " ) was the main axis of economic and political project of the Inca Empire . Along more than 6,000 kilometers , it allowed the Inca to control his Empire to move its troops from the capital , Cusco. A secondary network of cross roads, along more than 45,000 km, then connected the Qhapaq Nan to the coast and the Amazon basin.

Obsidian under the wings of the Condor - Colca Canyon / Peru - photo Adehm.de

Obsidian under the wings of the Condor - Colca Canyon / Peru - photo Adehm.de

Trade routes at the time of the Inca Empire - in green , roads in alitude - inblue, the coastal road - in purple, the tranversales - doc . Manco Capac

Trade routes at the time of the Inca Empire - in green , roads in alitude - inblue, the coastal road - in purple, the tranversales - doc . Manco Capac

 Qhapaq Nan ... somewhere on the Inca Trail - photo Unesco

Qhapaq Nan ... somewhere on the Inca Trail - photo Unesco

Peru and especially in Chile , obsidian was used as commodity money . Arrowheads and spears , objects of high demand was sustained value .

These trade routes ranging from Ecuador to southern South America : The Quebrada de Humahuaca is a long barren mountain valley , located in the NW part of Argentina ; it is an important physical link between the Andean highlands and temperate plains of south -eastern South America.

 

Sources :

- Caractérisation par analyse élémentaire (PIXE et ICP-MS/-AES) d’un verre naturel : l’obsidienne. Application à l’étude de provenance d’objets archéologiques./ Les obsidiennes d’Equateur et de Colombie - par L.Bellot-Gurlet / Thèse CNRS.

- Andean Obsidian Distributions through Time - link

- Qhapaq Ñan , la grande route des Andes -  link

- Unesco - Qhapaq Ñan , chemin principal Andin - link

- over.blog - Cordon Caulle - avancée de la coulée d'obsidienne rhyolitique un an après l'éruption.

- Unesco - La Quebrada de Humahuaca - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

The traffic of obsidian in North America has been studied mainly from the 50s.

The location of sites with obsidian merges in the range of volcanoes along the west coast of North America , and in the area of ​​intra- plate volcanism including the Snake river plain and the Yellowstone.

Traces of human activity dating back of 15,000 to 16,000 years , and the oldest trade in obsidian of 10,000 years , starting from the Mount Edziza , located in Canada, in the current British Columbia. This volcanic glass was traded from tribe to tribe , against shells, jewelry, turquoise, to Alaska and northern Alberta.

Obsidian knife of Mt Edziza - found in the area of ​​the Stikine river , presumed dated 2,000 years - Royal British Columbia Museum

Obsidian knife of Mt Edziza - found in the area of ​​the Stikine river , presumed dated 2,000 years - Royal British Columbia Museum

Some great sites of obsidian in USA - map Marler

Some great sites of obsidian in USA - map Marler

Many sites with obsidian are found from Oregon to California. It would be tedious to enumerate in detail , some sites being unproductive.

Large flows of obsidian , such as Little Glass Mountain / shield volcano of Medicine Lake in California , Big Obsidian Flow / Newberry Volcano in Oregon, and Obsidian Cliff / Yellowstone Nat . Park in Wyoming, are exceptional.

Distribution of obsidian, with some examples:

From Big Southern Butte ( 294 to 309,000 years ) in the Snake River plain, Shoshone and Bannock tribes , who used obsidian for their arrowheads and spears for about 10,000 years , have traded the glass in Idaho , Montana , Utah, and California .

Big Southern Butte / in the Snake river Plain - photo Bernard Duyck

Big Southern Butte / in the Snake river Plain - photo Bernard Duyck

Detail of an explanatory panel Big Southern Butte / in the Snake river Plain - photo Bernard Duyck

Detail of an explanatory panel Big Southern Butte / in the Snake river Plain - photo Bernard Duyck

The obsidian of Obsidian Cliff in Yellowstone National Park, has been used for 12,000 years by Native Americans for the manufacture of weapons and the manufacture of ceremonial objects ; it served as currency of exchange to the Misissipi, to the valley of the Ohio River , and Mexico , reflecting the movement of tribes not only in , but around the Yellowstone in the Paleolithic ( NPS / National Park Service) .

In addition to this main source , various smaller sites met at Yellowstone ( Cougar Creek , Reas Pass , Huckleberry Ridge , Warm Creek , Lava Creek ) and the Grand Teton Park , further south ( Conant Creek , Teton Pass )

Obsidian Cliff / Yellowstone NP - photo William S.Keller

Obsidian Cliff / Yellowstone NP - photo William S.Keller

Detail of a block of obsidian - Obsidian Cliff / Yellowstone NP - photo Bernard Duyck

Detail of a block of obsidian - Obsidian Cliff / Yellowstone NP - photo Bernard Duyck

In the Cascades range , the caldera of Newberry was frequented by native peoples in the past 10,000 years, contemporary way to Obsidian emissions. Although prior to the Big Obsidian Flow , dated only 1300 years , other obsidian flows were used : South obsidian flow is emitted in the southern caldera here 12,000 years ; Interlake obsidian flow and  Gama Hut floware dated about 7300 years, first at the expense of Central Pumice cone between Pumice and East Lake . The rhyolitic East Lake flow were issued from cracks parallel to the inside wall of the caldera, there 3,500 years.

Artifacts from this source have been found in Oregon and Washington state , to British Columbia ( IAOS ) . The abundance of these obsidian really drained as a magnet native peoples to Newberry from their winter camps located along the Deschutes river ... it is no longer the object that moves in this case , but the users .

 Block of obsidian - Newberry caldera - photo JM.Mestdagh

Block of obsidian - Newberry caldera - photo JM.Mestdagh

 The different flows of obsidian in the Newberry Caldera - doc.IAOS

The different flows of obsidian in the Newberry Caldera - doc.IAOS

Obsidian from Oregon - left, Little Glass Butte obsidian / Photo Geochemical research - right, obsidian and cristobalite / Photo Carion minérauxObsidian from Oregon - left, Little Glass Butte obsidian / Photo Geochemical research - right, obsidian and cristobalite / Photo Carion minéraux

Obsidian from Oregon - left, Little Glass Butte obsidian / Photo Geochemical research - right, obsidian and cristobalite / Photo Carion minéraux

Obsidian and Apache legend :

Apache tears are small obsidian cores embedded in a matrix of pearlite , white - gray color. This particular structure is set up in a lacustrine environment . They are found in southern Arizona.

" After the Apaches have conducted a series of raids against camps in Arizona , the soldiers assisted by some militia , following the track of stolen cattle and waited for dawn to attack the Apaches .
Apaches feeling safe in their mountain were attacked by surprise and outnumbered . Fifty warriors on seventy five were massacred , and the survivors fled following a cliff ; reached the edge of it , they preferred to throw himself into the void than to die at the hands of white men !
For years, those who ventured into the mountains "Big Pacacho " could see bones and bleached skeletons stuck in the crevices of the cliffs . The mothers, wives and girlfriends of these men settled near cliffs and for a full moon, mourned their dead .
Their grief was so great that the Great Spirit turned their tears in transparent black stones , these obsidian which when viewed through light, reveal the purity of women apache tears . "

Apache Tears - Arizona - photo Carion minerals

Apache Tears - Arizona - photo Carion minerals

Many factors have influenced the exchange of obsidian .

Craig Skinner studied the distribution of " archaeological obsidian " and the variables that influenced the course of time . Mainly found :

- Improvement of access roads to the obsidian sources
- Changing modes of transportation , moving from one pedestrian transportation to inland waterways

- Increasing of populations in the intermediate zones
- The local resource depletion
- Increased efficiency of trading systems
- The evolution of the socio- political organization and influence within a group or between groups on the exchange network .

The use of obsidian for the reconstruction of prehistoric contacts and exchange systems is more reliable in terms of stable populations , such as those that existed in Oregon and California. Transhumant groups such existing in the Great Basin of the United States have their exchanges related to their seasonal movements .

 

Sources :

- IAOS - International Association for Obsidian Studies - World obsidian sources catalog - link

- Obsidian lab - United States and Canada Obsidian and FGV source maps - link

- Obsidian studies in Oregon - by Graig Skinner

- The obsidian Cliff plateau prehistoric lithic source, Yellowstone Nat.Park. Wyoming

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

The history of obsidian merges with the history of early man . This volcanic glass was among the preferred raw materials from the Paleolithic , both for its technical qualities for the realization of effective tools, that for its aesthetic qualities . It will spread very locally first, then will accompany the colonization of new territories, and the creation of new trade roads.

The physico -chemical properties of obsidian allowed an identification of the sources and traceability by prehistorians of the human movements, exchanges of material, goods and expertise.

Distribution map of deposits of prehistoric obsidian - areas of influence and trade routes in the prehistory - doc . Glassway

Distribution map of deposits of prehistoric obsidian - areas of influence and trade routes in the prehistory - doc . Glassway

The cradle of European civilization is the Mediterranean basin.

The area of influence of Anatolia

The oldest traces of use of obsidian on the Mediterranean rim dated Upper Paleolithic , and are found in caves on the southwest coast of Anatolia. The main sources identified are in Cappadocia, with Gollu Dag, Nenezi Dag and Nemrut Dag . It is found in Neolithic sites , as Catalhöyük . 

Obsidian from Anatolian volcanoes will travel south to Palestine, and west to Crete .

Position of the deposits of Anatolia and the Caucasus - obsidatabase map.

Position of the deposits of Anatolia and the Caucasus - obsidatabase map.

Obsidian of the eastern islands come from Melos , with two nearshore sources , Dhemenegaki and Sta Nychia, exploited since the 11 millennium BCE. This Melos obsidian will circulate in the Aegean Sea between 11 ° and 8 ° millennium, certifying maritime trade between pre- Neolithic communities . Then she found in various parts of the Greek mainland and Knossos in Crete.

Obsidian from Giali, less favorable to the production of tools, only appears in the eight millennium , before being used as a semi- precious material at the 2nd millennium, by the Minoans in Crete .

In the western Mediterranean , obsidian is found in thousands of prehistoric sites , along an arc going from the eastern Maghreb , to Italy , southern France and of Catalonia , as well as in large islands , Sicily, Sardinia , Corsica, and the Aeolian archipelago . Exchanges are limited to coastal areas, and exceptionally more than 200 km. from the shore.

The main sources are in Sardinia, the Monte Arci volcanic complex , and three islanders sites : Pantelleria , Lipari in the Aeolian, and Palmarola in the Pontine Islands.

In Pantelleria , the main sources are Balata dei Turchi , south of the island, and Lagio di Venere , north -east . In Lipari, the obsidian is located in the lava flow of Gabellot
, while at Palmarola , it comes from the Monte Tramontana and Punta Vardella .

Monte Arci obsidian / Sardinia - photo Quatermara blogspot

Monte Arci obsidian / Sardinia - photo Quatermara blogspot

An Obsidian flow in Lipari - photo geologically

An Obsidian flow in Lipari - photo geologically

The obsidian of Lipari will spread in the Neolithic to Sicily and Calabria, Puglia and then to the Adriatic , even further north, in Friuli and the south of France . The obsidian of Palmarolla will travel to the Apennines, central Italy , Liguria and the south of France . From Sardinia, it will end up in Corsica and Tuscany. Obsidian from Pantelleria will spread further south to the neighboring islands and the coasts of eastern Maghreb. (see map above)

These areas will gradually spread over time, to wither abruptly, with the advent of the metal Ages , Bronze Age and Iron Age , and the diversification of cultural traditions that accompanies it.

 

Settlements around the Mediterranean by the Greeks and the Phoenicians - . Docs en plus map.

Settlements around the Mediterranean by the Greeks and the Phoenicians - . Docs en plus map.

Balkan regions will be supplied at the start of the deposits of the Carpathians , in Hungary and Slovakia.

Obsidian - Hungarian site - photo Univie.ac.at

Obsidian - Hungarian site - photo Univie.ac.at

Southeast of the Mediterranean, an area of ​​circulation moves on both sides of the Red Sea, departing Ethiopians deposits .

The priests of ancient Egypt used obsidian knives in embalming ceremonies . In the absence of Egyptian texts in this field, the writings of Herodotus ( 5th century BC ) report " a sharp blade in Ethiopian stone " in the mummification techniques that appear in the Middle Empire around 2700 BC .

The Metropolitan Museum of Art in New York has in its collections obsidian vases, gold rimmed, dated of 12 ° to 18 ° dynasties, between 1990 and 1293 BC.

It was used to make the eyes of many statues ; the most significant achievement is the funerary mask of Tutankhamun - 1323 BC. JC .

Tutankhamun - one of his funerary masks - irises in Obsidian - photo Bernard Duyck

Tutankhamun - one of his funerary masks - irises in Obsidian - photo Bernard Duyck

Sources :

- Circulation et origine de l'obsidienne préhistorique en Méditerranée, un bilan de cinquante années de recherche - par Gérard Poupea & al.

- La circulation de l'obsidienne dans le sud de la France au Néolithique - par Didier Binder & al.

- University of London - The Obsidian Evidence for the Scale of Social Life during
the Palaeolithic - by Theodora Moutsiou

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

Ailsa Craig is located 16 km. off Ayrshire Coast, midway between Glasgow and Belfast, in the Firth of Clyde , an arm of the Irish Sea.

The name of the island is the anglicized form of Gaelic Aillse Creag or Creag Ealasaid which means Elizabeth's rock.

However the island is so visible and serves as a benchmark for so long in the strait between Scotland and Ireland it is mentioned in many ancient Celtic texts under various names: A ' Chreag (" the rock ") , Creag Alasdair (" the rock of Alasdair ") Ealasaid a ' Chuain (" Elizabeth of the ocean ") or Alasan .

This island, 3,200 meters in circumference, culminates at The Cairn , its top at 338 meters ... which ranks among the "marilyn" , or fell a mountain whose height exceeds 150 meters, humorous allusion to the name of the actress Marilyn Monroe.

Ailsa Craig island - photo Paul Hart

Ailsa Craig island - photo Paul Hart

It consists of the remains of an ancient volcanic plug , as evidenced by the basalt outcropping on its current coastline.

Volcanism is related to the opening of the North Atlantic began here about 62 million years ago, a geological episode that separated North America from Europe . Paleogene igneous intrusions , volcanoes and lava flows gave the islands that dot the western shores of Scotland ...

Skye, Mull, Rum and Ailsa Craig are leftovers. The Ardnamurchan Peninsula and basalt floods in Northern Ireland , the Giant's Causeway , were formed in the same period.

Ailsa Craig island, view from the south - photo Maybole.org

Ailsa Craig island, view from the south - photo Maybole.org

Sources :

- British Geological Survey – Geology, petrology and geochemistry of Aisla Craig - link

- Scotland, the home of geology - link

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Publié le par Bernard Duyck
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The Inner Hebrides , an archipelago located in the west of Scotland, home to the islands of Mull and Staffa , famous for its volcanic organs and Fingal 's cave .

The island of Staffa , 1,000 m on 500 , is lying on a NS axis. Its coast is home to many caves, carved by wave action .

Fingal 's cave is located at the southern tip of the island. High twenty meters and long of 75 m. , it is carved into a basalt cliff.

The French volcanologist Faujas Barthelemy Saint -Fond studied organs of Staffa in the 18th century and concluded that these regular columns were formed by lava.

Volcanic organs of Fingal 's Cave, on Staffa island - photo Sutterchance.com

Volcanic organs of Fingal 's Cave, on Staffa island - photo Sutterchance.com

 Volcanic organs of Fingal 's cave - photo Catalyzing changes .

Volcanic organs of Fingal 's cave - photo Catalyzing changes .

 Inside Fingal 's cave , with a fisheye - photo The Monde.fr

Inside Fingal 's cave , with a fisheye - photo The Monde.fr

His name in Gaelic An Uamh Bhin means " melodious cave " ... the sound of the waves in the cave has not interested only the geologists , he inspired a work of Felix Mendelssohn: Die Hebriden / opening opus 26 , also called Die Fingalshöhle .

He says " arrived in Scotland with a penchant for folk songs , an ear for the beautiful and fragrant countryside and a heart for the bare legs of the natives" .

The island of Staffa is entirely volcanic : on a base of tuff , tholeiitic basalts with dark olivine are topped by a layer of basaltic lava without crystalline structure. The intermediate layer has predominantly hexagonal columns , which form the walls of caves excavated . These basalts are dated to 55-58 million years ago.

 The island of Staffa - photo Scotland.org.uk / Shutterstock

The island of Staffa - photo Scotland.org.uk / Shutterstock


A pyramidal islet , only visible at low tide, called Am Buachaille - the shepherd - is formed from a pile of basaltic columns sheaves.

 Staffa island - Am Buchaille - photo H.J.Bennöhr

Staffa island - Am Buchaille - photo H.J.Bennöhr


Mull island, who formed the prehistory one set with the current islands of Iona and Treshnish , was formed there 50-60 Ma under the action of fissure eruptions during the formation of the North Atlantic and division of the supercontinent of North America-Europe 

The stepped plateaus of  Mull were subsequently treated by the central igneous complex , and earthquakes , before being eroded by glaciers that retreated 10,000 years , leaving deep U-shaped valleys , and a paradise for geologists .

Mull island wild columns - photo Ardmeanach wilderness - BBC Scotland blog

Mull island wild columns - photo Ardmeanach wilderness - BBC Scotland blog

Sources :

- Scotland inverness - Staffa Fingal's cave and the Treshnish islands - link

- Scotland, the home of geology - link

- Southern Hebrids - Staffa, a geological marvel - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

Echoing an article by Jessica Ball on its "Magma cum Laude" website , Scotland is required
as a geological dream destination.

This relatively small area has a strong geological variety. Its oldest rocks are Lewisian gneiss, dating from Archean , more than three billion years. In Precambrian , they are Torridonian sandstone that form, followed in the Cambrian , by sedimentary deposits. This area is part in Silurian, between 443 and 416 Ma, of the continent Laurentia , bordered by the Iapetus Ocean. During the Caledonian orogeny , the continent Laurentia collides with the continent Baltica ... after this collision , volcanic activity is recorded in Scotland , characterized by volcanoes and other igneous intrusions.

Evolution of continents between 450 and 370 Ma - on the map of the left is the current UK (in red) still separated into two entities .

Evolution of continents between 450 and 370 Ma - on the map of the left is the current UK (in red) still separated into two entities .

Edinburgh , the Scottish capital, as a geological hot spot :

The city is built on a series of volcanic hills, which are as many points of view on the city.

Edinburgh is dominated by its castle built from the 7th century on Castle Rock, a volcanic neck dated 350 Ma ( Carboniferous) , remains of a diatreme overlapping sedimentary rocks and formed of dolerite . The passage of glaciers on mixed terrain left  a " crag and tail " formation , a hard and tough rock protecting a tail, as opposed to the attack of the glacier. This rock, exceeding 80 meters on average around, formed a formidable fortress , but with a disadvantage to the impermeable nature of the dolerite , and the water ran out despite a well 28 meters deep during the siege of 1573.

Edinburgh - Castle Rock and Castle - Photo ebookers

Edinburgh - Castle Rock and Castle - Photo ebookers

Scheme of a "crag and tail " formation - A: Crag formed by hard volcanic rocks - B : tail formed by sedimentary rocks - C : direction of movement of the glacier - doc . Jonathan Oldenbuck

Scheme of a "crag and tail " formation - A: Crag formed by hard volcanic rocks - B : tail formed by sedimentary rocks - C : direction of movement of the glacier - doc . Jonathan Oldenbuck

To the southeast of the city, and contemporary of Castle Rock, is a hill of 250 meters and resembling a lion lying down : Arthur 's Seat.

Two former craters form the head, Lion's head , and hip, Lion's haunch . Basaltic lavas and tuffs were eroded by Pleistocene glaciers , leaving the cliffs to the west and detritus of a medial moraine to the east.

Arthur 's Seat is often mentioned as a possible site for Camelot , the legendary castle of King Arthur and the Knights of the Round Table.

This set is part of the current Holyrood Park, property of the king at the origin and site of SSSI / Site of special scientific interest.

Edinburgh - Arthur's Seat - saw from Pollock Halls - photo David Monniaux

Edinburgh - Arthur's Seat - saw from Pollock Halls - photo David Monniaux

Between Arthur 's Seat and the city center of Edinburgh, Salisbury Crags form the same type a basalt cliff .

A dolerite sill , known as " section Hutton " - James Hutton is considered as one of the fathers of modern geology , and a native of Edinburgh - , shows how magma forced its way in sedimentary rocks.

Front to back : Edinburgh , Salisbury Crags and Arthur's Seat - Wikipedia Photo

Front to back : Edinburgh , Salisbury Crags and Arthur's Seat - Wikipedia Photo

Tomorrow other Scottish sites ... if the news permits.

 

Sources:

- AGU Blogosphere - Magma cum Laude - Edinburgh: Old Town and older volcanoes

- Scottish Geology - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Deception island : a story related to storms and icebergs.


The first official mention of Deception Island was made by the British sailors William Smith and Edward Bransfield in January 1820. It was named by an USA's sailor , Nathaniel Palmer, later in the same year.

From the beginning of the 19th century , Deception Island became a favorite refuge in Antarctica, where sailors were waiting for the end of storms and
of the passage of icebergs. The first scientific expedition was conducted in 1829 by the British Captain Henry Foster, aboard HMS Chanticleer . The island was used by sealers , then in 1906, by a Norvegio-Chilean whaling company as a basis for the Gobernator Bories, a factory ship .

Between 1908 and 1910 , the French explorer Jean- Baptiste Charcot made ​​a stop to coal supplies , water and food , or repair the "Pourquoi pas " .After 1912 , 150 people worked at the whaling station of the Hektor whaling company during the austral summer , producing up to 140,000 barrels of whale oil . This production stopped in April 1931 when the oil prices dropped .

Deception island - the Whaling Station and, in the foreground , whalebones - photo http://www.deceptionisland.aq

Deception island - the Whaling Station and, in the foreground , whalebones - photo http://www.deceptionisland.aq

Deception Island - Whaler Bay and its black sand beaches - photo Antony Van Eeten 03.2014

Deception Island - Whaler Bay and its black sand beaches - photo Antony Van Eeten 03.2014

In the 40s and 50s , the Antarctic Peninsula has been the subject of territorial claims by Argentina , Chile and England . Deception island played a central role in international affairs of the Antarctic . In 1944 , the British established their first base on the old whaling station . Argentines built a station in Fumarole Bay in 1948. In 1955 , Chile built the Pedro Aguirre Cerda Station at Pendulum Cove .

The 1969 eruption will destroy the Chilean and British bases , which remains the rusty tanks and boilers ,  an airplane hangar, and the house of  the scientific station disemboweled.

Deception island - ruins of whaling facilities - photo Antony Van Eeten 03.2014

Deception island - ruins of whaling facilities - photo Antony Van Eeten 03.2014

Deception island - some whaling boats still exist - photo Antony Van Eeten 03.2014

Deception island - some whaling boats still exist - photo Antony Van Eeten 03.2014

The climate of Deception Island is called " maritime polar ." The average temperature of the air is less than 3 ° C , with +11 ° C max and min at -28 ° C. The rate of precipitation is 500 mm / year. The prevailing winds are westerly to north-east.

Extreme microclimates exist around fumaroles and geothermal waters , where the air temperature can reach 40 ° C , and the water 70 ° C.

Antarctic Sagine - Colobanthus quitensis - Antarctic pearlwort - photo Liam Quinn

Antarctic Sagine - Colobanthus quitensis - Antarctic pearlwort - photo Liam Quinn

Arctic flora and fauna :

The flora is exceptional , although sparse . There are 18 species of moss and lichen , found nowhere else in Antarctica , including two endemic.The Antarctic pearlwort - Colobanthus quitensis  - is the only growing in the geothermal areas of the island, forming the largest community known for this species .

Nine species of pelagic birds nest on the island.

The world's largest colony of Chinstrap Penguin , Pygoscelis antarcticus  -  is located on the southwest coast of Deception Island at Baily Head, and is estimated at 100,000 breeding pairs .

It also meets the Gentoo Penguin - Pygoscelis papua  - and the Antarctic skua - Stercorarius antarcticus .

Deception Island - Chinstrap penguins nesting - photo travelwild

Deception Island - Chinstrap penguins nesting - photo travelwild

Deception Island - Gentoo penguins - photo Antony Van Eeten 03.2014

Deception Island - Gentoo penguins - photo Antony Van Eeten 03.2014

Deception Island - South American sea lion - Otaria flavescens - photo Antony Van Eeten 03.2014

Deception Island - South American sea lion - Otaria flavescens - photo Antony Van Eeten 03.2014

Deception Island is not a place of desolation, it is the site of active scientific base and a tourist destination increasingly popular .

World in black and white (snow and volcanic ash ) , with touches of red (hematite ) and yellow ( cheptonite ) - photo Antony Van Eeten 03.2014

World in black and white (snow and volcanic ash ) , with touches of red (hematite ) and yellow ( cheptonite ) - photo Antony Van Eeten 03.2014

 Deception Island - a place of memory - photo Antony Van Eeten 03.2014

Deception Island - a place of memory - photo Antony Van Eeten 03.2014

Sources :

- Deception island - site officiel - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages

In Antarctica, South Shetland archipelago is home to a volcanic rounded island by 15 km in diameter , Deception Island .

This shield volcano is an iron horse- caldera 10 km. x 8 , flooded by the sea, which earned him the nickname " Icy Santorini of Antarctic "

Few travelers venture into these icy and isolated landscapes ... our friend Antony Van Eeten , who shares with us his photographs of volcanic trips, is back and gives us the scoop of his images taken in March of this year.

Deception Island - photo Antony Van Eeten March 2014

Deception Island - photo Antony Van Eeten March 2014

Tectonics, formation and activity of the volcano Deception:

The island-volcano is in the middle of the Bransfield Strait , 125 miles north of the Antarctic Peninsula. This strait is a mini -rift opening at the rate of 1 cm. per year , the last of a series of transform faults and mini- rifts which succeed south of the tectonic plate Scotia and joined far in the east the triple junction point between the African, South America and Antarctica plates. This phenomenon of opening is doomed to extinction , according to geologists , in a few hundred thousand years , as the volcanism thet causes.

Tectonics near Deception Island - doc Alps Geo .

Tectonics near Deception Island - doc Alps Geo .

Map of Deception Island

Map of Deception Island

There are about nine thousand years , a violent explosive eruption sprayed 30 km ³ of molten rock from the volcano Deception . The summit of the volcano collapsed, following the discharge of its magma chamber , forming the Port Foster caldera, a bay protected from the winds and waves of the Southern Ocean .

The first eruptions were observed in 1790 , while others took place in 1828, 1842. In the 20th century two periods , from 1906 to 1910 and from 1967 to 1970, include the activity along circular fractures along the edges of the caldera . No eruption has marked the center of it , a sign of subsidence in cascade of a central block, in the manner of a piston sliding along a ring fault , and releasing by intervals the magma on its edges . (Alpes- geo / D.Corneloup )

Eruptions of 1967 and 1969 inflicted much damage to Chilean and British scientific stations.

In 1992 , an increase of seismicity was accompanied by ground deformation , and an increase of temperatures ... marking an intrusion that has not resulted in an eruption. In 1970, eruptions have been observed by scientists during the austral summer. The geothermal measurements show the presence of an average thermal gradient of 360 ° / km. ... suggesting a magma chamber at a depth of 3 to 4 km .

The caldera of Deception remains " unrest and at risk." The caldera has areas of thermal activity , including hot springs on the beach , with water between 30 and 70 ° C , and fumaroles of steam and sulfur on the internal and external sides .

Deception island - arrival to the entry of the caldera, Neptune's Bellows - photo 03.2014 A.Van Eeten

Deception island - arrival to the entry of the caldera, Neptune's Bellows - photo 03.2014 A.Van Eeten

Deception Island - activity in the 20th century - cracks and submarine faults - doc . Antarctica astrobiology

Deception Island - activity in the 20th century - cracks and submarine faults - doc . Antarctica astrobiology

Morphology of Deception Island.

The large bay of Port Forster, at the center of the flooded caldera, covers most of the island, about 9 km x 6 . It has a narrow entrance , Neptune's Bellows (Forges of Neptune ) , 230 meters wide . Raven Rock, a rock in the middle of the inlet, submerged under 2.5 m. water, makes the access complicated.

At the entrance of the Forges of Neptune, is Whalers Bay , lined with beaches of black volcanic sand

Deception Island - Neptune's Bellows and Sewing Machine Needles - photo 03.2014 Antony Van Eeten

Deception Island - Neptune's Bellows and Sewing Machine Needles - photo 03.2014 Antony Van Eeten

Deception Island - Pete 's Pillar at the entrance of Port Foster - photo 03.2014 Antony Van Eeten

Deception Island - Pete 's Pillar at the entrance of Port Foster - photo 03.2014 Antony Van Eeten

Deception Island - detail on the inner walls of the caldera - 03.2014 Photo Antony Van Eeten
Deception Island - detail on the inner walls of the caldera - 03.2014 Photo Antony Van Eeten

Deception Island - detail on the inner walls of the caldera - 03.2014 Photo Antony Van Eeten

From east to west , making a tour of the island, follow the heights of Mount Pond, 539m . , then the highest point of the island , unnamed, 576 m.

Goddard Hill, with 332 m is located NE of Deception . Two ridges ,  Teleton and Stonethrowridges ridges, form the west side and to close the iron horse , Mount Kirkwood, with 452 m.

The current maximum depth of the caldera is less than 200 meters , the result of a sedimentary post-caldera processes.

Deception Island - climbing to the heights and overlooking the caldera and Neptunes Bellows 's, behind the group - Photo 03.2014 Antony Van Eeten

Deception Island - climbing to the heights and overlooking the caldera and Neptunes Bellows 's, behind the group - Photo 03.2014 Antony Van Eeten

Tomorrow , history and nature of Deception Island


Sources:
- Thanks to Antony Van Eeten for its photo sharing

- Global Volcanism Program - Deception island

- Alpes Geo - Un volcan actif de l'Antarctique : Deception island - par Désiré Corneloup - link

- Cambridge Volcanology Group - Deception island

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