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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

The vicinity of Schotten hide well in the woods of Kölzenhain an eroded set of basanite together, probably a dyke, a rise of lava in favor of tectonic fractures.

Two different structures are discovered about a hundred meters apart: Schleuningsteine ​​and Mullstaa.

 

Vogelsberg - Schleuningsteine ​​- photo © Bernard Duyck 05.2014

Vogelsberg - Schleuningsteine ​​- photo © Bernard Duyck 05.2014

Vogelsberg - Schleuningsteine ​​- photo © Bernard Duyck 05.2014

Vogelsberg - Schleuningsteine ​​- photo © Bernard Duyck 05.2014

Schleuningsteine:  basanite, charasteristic of the intraplate volcanism, localised and of low volume, as columns vertical  with a height of up to 5 meters above the ground, form a natural monument.

Olivine and plagioclase cores are included in the matrix, and the cavities left by the gas are filled by zeolites.

A commemorative plaque in honor of the mayor of Feldkrüchen, Wilhelm Scleuning, designates the place.

GPS: 50 ° 33'38 .50 "/ 9 ° 10'39 .93"


 

Vogelsberg - Mullstaa - a basalt wall 6 meters high - photo © Bernard Duyck 05.2014

Vogelsberg - Mullstaa - a basalt wall 6 meters high - photo © Bernard Duyck 05.2014

Vogelsberg - Mullstaa - the rubble - Photo © Bernard Duyck 05.2014

Vogelsberg - Mullstaa - the rubble - Photo © Bernard Duyck 05.2014

Vogelsberg - Mullstaa - large blocks among the rubble - Photo © Bernard Duyck 05.2014

Vogelsberg - Mullstaa - large blocks among the rubble - Photo © Bernard Duyck 05.2014

Mullstaa, or Mullsteine, form a 6 meter high rock surrounded by scree of basanite, in which large blocks of lava fell. These lavas are of the same composition as that of Schleuningsteine, 100 m. further west.

According to our friendly guide, Mr. Müller, between Schleuningsteine and ​​Mullsta sites, the Celts have aligned blocks of basalt in increasing size.

 

Vogelsberg - Between Schleuningsteine ​​and Mullstaa, the Celts aligned blocks of basalt - photo © Bernard Duyck 05.2014

Vogelsberg - Between Schleuningsteine ​​and Mullstaa, the Celts aligned blocks of basalt - photo © Bernard Duyck 05.2014

Local legends are linked to these sites and the cult of the goddess Holle or Hulda (Holda), worshiped in the pre-Christian era by the Celts.
Expansion of the Celts / culture Halstadt - doc. yves-van-nimmen.e-monsite.com

Expansion of the Celts / culture Halstadt - doc. yves-van-nimmen.e-monsite.com

Expansion of the Celts / culture Halstadt - doc. yves-van-nimmen.e-monsite.com

The origin of its name and its quality are variables related  : to each according to Hel, the German godess of death (compare the the German word Hölle designating hell), according to other sources, derived from Middle High German Hulde, meaning "benevolent".

The supernatural character and legendary is ambivalent: the goddess dates back to the surface between December 23 and January 5, in the "Twelve nights period" should stop chores, to check who had been employed, or idle during year ... rewarding or punishing as appropriate punishment for negligent, reward for the needy!

 

 "Holda, the gütige Beschüzerin" - "Holda, benevolent protector" (Friedrich Wilhelm Heine, 1882)

"Holda, the gütige Beschüzerin" - "Holda, benevolent protector" (Friedrich Wilhelm Heine, 1882)

The goddess Holle is responsible of snow fallout in the  winter : more it seeks to shake his bed quilts, the more snow down here. This legend is included in the Grimm fairy tale, "Frau Holle".

Symbol of virtue and hard work, Hulda is perhaps the only Germanic goddess whose cult has survived until today. His association with the house and the women may be the cause of their status, often maligned during the modern period.

Sources:
- Special thanks to Lothar Müller Heern and his wife, for their valuable assistance.

- Vulkan Vogelsberg - link

- "Wanderung zu ur- und frühgeschichtlichen Stätten Oberhessens" – par le Dr. Max Söllner

- Holda, white Lady of winter - link

Vogelsberg volcanic massif - 8 - Schleuningsteine ​​and Mullstaa.Vogelsberg volcanic massif - 8 - Schleuningsteine ​​and Mullstaa.

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

Exploring the northern part of the massif starts at Herbstein, built on an old volcanic vent (map). This small town has a medieval center gathered in a circle around the church of 14 century.
 

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

The Gallberg, south of Herbstein, is pierced by some quarries.

Part of the site, which is no longer used, include a small lake.

In the quarry in operation, a high basalt cliff about 8 meters high, topped by a thin layer of loess, has a tormented ... and probably ephemeral face.

 

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Gallberg - photo © Bernard Duyck 05.2014

A thermal spring was drilled in 1976;  water at 32.6 ° C was found to a depth of approximately 1000 meters. Its natrium and calcium fluoride content  led to the development in 1980 of volcanic thermal baths (Vulkantherme) recognized in orthopedics.

To Altenschlirf, the Wilde stein is reached by a paved road. A cliff of 30-m long and 5 meters high of tholeiitic basalt can be discovered, hosted in the hill.

GPS: 50 ° 32'5 .52 "- 9 ° 23'37 .14"
 

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - photo © Bernard Duyck 05.2014

Sources :  

- Petrogenesis of basanitic to tholeiitic volcanic rocks from the Miocene Vogelsberg, Central Germany - by P.J.F. Bogaard & G. Wörner / Journal of Petrology.

- Der Vogelsberg - Geotope im grössten vulkangebiet mitteleuropas - Th. Reischmann & Ad. Schraft.

Vogelsberg - Herbstein / Wilde Stein - piece of basalt organ with 5-6 faces  -. Photo © Bernard Duyck 05.2014

Vogelsberg - Herbstein / Wilde Stein - piece of basalt organ with 5-6 faces -. Photo © Bernard Duyck 05.2014

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Vogelsberg, " the bird's mountain ", is the largest European basaltic massif and the only German shield volcano. Heavily eroded, its highest peaks are Taufstein with 773 m. and Hoherodskopf with 763 m.

It is mainly covered with hardwoods and surrounded by the so-called belt-Grünland Fichten, a landscape of hedges feature of Vogelsberg. Meadows, fields, forests, a plant universe of multiple species as well as ponds and lakes are the natural setting. With a dense network of hiking trails, the natural park Hoher Vogelsberg let admire a very diverse flora and fauna.
 

Vogelsberg - overview of Hoherodskopf, one of the peaks of the massif - photo © Bernard Duyck 05.2014

Vogelsberg - overview of Hoherodskopf, one of the peaks of the massif - photo © Bernard Duyck 05.2014

Vogelsberg - Hoherodskopf: telecommunications tower, 144 meters high - photo © Bernard Duyck 05.2014

Vogelsberg - Hoherodskopf: telecommunications tower, 144 meters high - photo © Bernard Duyck 05.2014

Hoherodskopf :

Located near the Information Centre for the Conservation of Nature, this spot is  touristically overexploited (installation for winter sports, acrobranche course, walking, cafes, restaurant, bus stop Vulkan-Express  ... a trailer for cyclists tired or sore shortcuts), but poorly marked geologically ... we must have his nose on Geotop for an indication!

Dark gray basalt outcrops yet near the tower. With a microscope, olivine and plagioclase are revealed.

A peculiarity: the basanite has such a high content of magnetite as a compass needle is deflected.

 

Vogelsberg - basanite outcrop - photo © Bernard Duyck 05.2014

Vogelsberg - basanite outcrop - photo © Bernard Duyck 05.2014

Taufstein is the highest peak in the Vogelsberg, with its 773 meters.

Outcrops of dark basanite, with olivine and clinopyroxene
phenocrysts, in large blocks, are visible in part of natural forest left.

At the top stands the Bismarck Tower (1906 -1910) built in basalt blocks ... one of 240 high towers in the German Empire in honor of Chancellor Otto von Bismarck

A place where Saint Boniface (see ante) have preached and baptized in the 8th century is marked by a few large blocks and called "Bonifatiusborn"


 

Taufstein - mossy basalt blocks to leave just guess - photo © Bernard Duyck 05.2014

Taufstein - mossy basalt blocks to leave just guess - photo © Bernard Duyck 05.2014

Taufstein - a summary cleaning was necessary to reveal the nature - photo © Bernard Duyck 05.2014

Taufstein - a summary cleaning was necessary to reveal the nature - photo © Bernard Duyck 05.2014

Taufstein - The austere Bismarck Tower in  basalt blocks - photo © Bernard Duyck 05.2014

Taufstein - The austere Bismarck Tower in basalt blocks - photo © Bernard Duyck 05.2014

Taufstein - Bonifatiusborn - photo Dr. Mabuse

Taufstein - Bonifatiusborn - photo Dr. Mabuse

Sources :  

- Petrogenesis of basanitic to tholeiitic volcanic rocks from the Miocene Vogelsberg, Central Germany - by P.J.F. Bogaard & G. Wörner / Journal of Petrology.

- Petrogenesis of tertiary continental intra-plate lavas from the Westerwald region, Germany  / Journal of Petrology.

- Der Vogelsberg - Geotope im grössten vulkangebiet mitteleuropas - Th. Reischmann & Ad. Schraft.

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

Near Nidda, the Vulkan dorf (volcanic village) of Michelnau houses the quarry of red tuff of the same name.

Vogelsberg massif produced mainly basalt, but also the red tuff. It is a cluster of slag produced during explosive eruptions, of phreatomagmatic type.

The red tuff of Michelnau contains 64% glass matrix, 32% zeolite and indefinite materials, 2% pyroxene, and other accessory minerals including olivine. Zeolites are found in the pores, forming half of the tuff. The red color of the tuff from its iron content.

Vogelsberg - the red tuff of Michelnau - photo © Bernard Duyck 05.2014

Vogelsberg - the red tuff of Michelnau - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau - Explanatory panel of the observation deck - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau - Explanatory panel of the observation deck - photo © Bernard Duyck 05.2014

Vogelsberg - tuff blocks to the parking entrance - Photo © Bernard Duyck 05.2014

Vogelsberg - tuff blocks to the parking entrance - Photo © Bernard Duyck 05.2014

The explotation :

Johann Weisel, a German farmer and innkeeper, began the extraction of stones in 1863. Due soft features of this tuff, he could not use explosives ... the very physical work is done with a saw , with the advantage of being able to choose the size of the extracted block, function of his application. Wholesale bullion rectangular shape are found in the rock wall, released by several sides. Tuff deposit is about 100 m wide on 30, and was operated on several levels.

An old machine hints at the hard work necessary to break these blocks, and carry them out of the quarry.

The extraction was stopped in the middle of the 1990s. Since 2010, the career has become a "GeoTop" accessible only on guided tours. An observation deck is happily accessible to all, starting from a well-marked parking, and offers a breathtaking view of the face.

GPS position: 50 ° 25'18 - 9 ° 2'23.
 

Vogelsberg - access to the quarry of red tuff Michelnau - photo © Bernard Duyck 05.2014

Vogelsberg - access to the quarry of red tuff Michelnau - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau's quarry - to the observation deck: operating on several levels, notched walls - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau's quarry - to the observation deck: operating on several levels, notched walls - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau's quarry - photo © Bernard Duyck 05.2014

Vogelsberg - Michelnau's quarry - photo © Bernard Duyck 05.2014

Vogelsberg - career Michelnau - blocks were transported by trucks before being cut to measure - photo © Bernard Duyck 05.2014

Vogelsberg - career Michelnau - blocks were transported by trucks before being cut to measure - photo © Bernard Duyck 05.2014

This tuff has been used for the construction of bridges, churches, gravestones.

Previously, the tuff was used for making stone ovens, because of its heat resistance and good preservation thereof. It is still prized by sculptors and landscape architects.
 

Career Michelnau - block tuff with traces of saw - photo © Bernard Duyck 05.2014

Career Michelnau - block tuff with traces of saw - photo © Bernard Duyck 05.2014

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Vogelsberg massif -  following the "Vulkanradweg", from Fulda (east), the spots are Grebenhain and today Gedern before pushing west towards Nidda.

Vogelsberg massif - following the "Vulkanradweg", from Fulda (east), the spots are Grebenhain and today Gedern before pushing west towards Nidda.

We continue our "hunting of basalt" in southern Massif Vogelsberg ... after Grebenhain and St.Boniface Chair, here the Gedern's quarry.

Used by the Counts of Stolberg since the 17th century for the extraction of stone for construction,

this quarry is still partially active. It is reached by a small road, trying to spot the little yellow placard with a black hammer ... much easier with the GPS coordinates: 50° 24'50 - 11'33° 9.
Vogelsberg - career Gedern - basalt flows superimposed - Photo © Bernard Duyck 05.2014

Vogelsberg - The quarry of Gedern - basalt flows superimposed - Photo © Bernard Duyck 05.2014

Vogelsberg - The quarry of Gedern - basalt flows superimposed - Photo © Bernard Duyck 05.2014

Vogelsberg - The quarry of Gedern - basalt flows superimposed - Photo © Bernard Duyck 05.2014

Vogelsberg - The quarry of Gedern - basalt flows superimposed - Photo © Bernard Duyck 05.2014

The hole is huge: 500 m. and length of 20 m. depth.

We can detect several superimposed lava interspersed by slag red-brown.

With a little searching, we find spherical bombs mixed in the slag layer, as well as beautiful zeolites in the basanite.
Vogelsberg - career Gedern - volcanic bomb embedded in the slag - photo © Bernard Duyck 05.2014

 

Vogelsberg - The quarry of Gedern - volcanic bomb embedded in the slag - photo © Bernard Duyck 05.2014

Vogelsberg - The quarry of Gedern - volcanic bomb embedded in the slag - photo © Bernard Duyck 05.2014

 Vogelsberg - the quarry of Gedern - basalt and slag - photo © Bernard Duyck 05.2014

Vogelsberg - the quarry of Gedern - basalt and slag - photo © Bernard Duyck 05.2014

Vogelsberg - the quarry of Gedern - Close-up of basalt - photo © Bernard Duyck 05.2014

Vogelsberg - the quarry of Gedern - Close-up of basalt - photo © Bernard Duyck 05.2014

After the basalt,  tomorrow the red tiff of Nidda.

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Vogelsberg / Grebenhain "Bonifatius Kanzel" -  the St.Boniface Chair - photo © Bernard Duyck 05.2014-

Vogelsberg / Grebenhain "Bonifatius Kanzel" - the St.Boniface Chair - photo © Bernard Duyck 05.2014-

First spot in the Vogelsberg massif :  Grebenhain / BONIFATIUS KANZEL


GPS: 50 ° 29'12 / 9 ° 16'58 - easily accessible on foot from the parking of the height of Herchenhain.

This broad basanite outcrop called "the chair of St. Boniface" (*), is 10 meters long, 4 meters high and 3 meters wide.

This training forms the SW extremity of a series of rocks, aligned SW-NE on 40 meters. It has a dark gray color to almost black. The diameter of some of the columns of 3,5 or 6 sides is generally less than 20 cm.
Vogelsberg / Grebenhain: Bonifatius Kanzel columns faceted eroded - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel columns faceted eroded - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel columns faceted eroded - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel columns faceted eroded - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel columns faceted eroded - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel / end of the outcrop - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel / end of the outcrop - photo © Bernard Duyck 05.2014

Like other places in the area, his name is linked to St. Boniface, the evangelizer of Germany.

Born in England to 675 in the early Middle Ages, as Wynfreth (Winfrid), this man became a monk, priest and a renowned scholar. Pope Gregory II recognized his organizational talents and entrusted him with the mission in 719 to evangelize the Saxons in Germany. He placed under the protection of Charles Martel, grandfather of the future emperor Charlemagne.

He took the name of Boniface - "Bonifatius", of Bonnus and Fatus, good destiny - an ancient martyr, and share evangelize Hesse and Thuringia,  multiplying religious foundations; He is the founder and Others Abbey of Fulda.

Promoted archbishop, he chairs a council in 739 to reorganize the local episcopate. He founded the bishoprics of Würzburg, and Erfurt Burabourg.

On the death of Charles Martel in 741, Carloman, his eldest son, who inherited Austrasia, Swabia and Thuringia, asked Boniface also to reform the Frankish church, and appointed Metropolitan of Austrasia ( the region between the Meuse and Rhine).

Boniface convened a council in 742 and in 743. On this occasion, the fate of the church property granted by the Pippinides to their "clients" is governed by the recognition of a derisory pay to the Church hundred and commitment recipient serve the king in return ... The historians see in this arrangement, the first example of a personal commitment vassal type of the landowners to the king and the beginnings of feudalism.

Became ArcMainz, Boniface has the honor of conferring the royal anointing to Pepin, younger brother of Carloman.

 

Becoming bishop of Mainz, dissatisfied, he resumed his stick pastor to convert the  Frisians. The old man was killed with 52 companions on the day of Pentecost 754 (June 5), near Dokkum in Friesland. The apostle of the Germans will be buried in Fulda.

Its main attributes are the garb of bishop's, miter and a book crossed with a sword (weapon when he was killed). It is sometimes represented baptizing converts, one foot on a fallen oak (the oak of Thor) which is the symbol of the defeat of the pagan religion. (Herodote.net)

 

Vogelsberg / Grebenhain: Bonifatius Kanzel - photo © Bernard Duyck 05.2014

Vogelsberg / Grebenhain: Bonifatius Kanzel - photo © Bernard Duyck 05.2014


(*) Chair, from the Greek Cathedra = seat, is the seat of a bishop in his church, by extension, the gallery of a preacher.

 

Sources :

- Vulkanring-Vogelsberg - link 

- Saint Boniface - link

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
The summits of the Vogelsberg - with the communications tower of Hoherodskopf, the second highest peak at 763 m - photo Bernard Duyck 05.2014

The summits of the Vogelsberg - with the communications tower of Hoherodskopf, the second highest peak at 763 m - photo Bernard Duyck 05.2014

With its diameter of 60 km wide, the Vogelsberg today is the largest closed basaltic massif of continental Europe. Although known as a great central volcano, Vogelsberg consists of several eruptive centers.

In activity at the end of the Tertiary, between 19 and 10 Ma, the emited lavas covered 2,500 km ².

In the center of the shield volcano that resulted, the thickness of lava reaches 700 meters (drilling research in 1996, which has not reached the basement volcanic rocks). On the western edge layer is thinner, about 150 meters against 400 meters on the eastern edge.

Schematic representation of the components of the crust and mantle beneath the Vogelsberg - after Boggard and Wörner - reference in sources. 1, Upwelling asthenosphere (EAR - European Asthenospheric Reservoir - signature); 2, lower lithospheric mantle (depleted); 2a, metasomatized regions of the TBL (anhydrous); 3, hydrous mineral bearing veins (∼70 Ma?); 4, upper lithospheric mantle (depleted); 4a, metasomatized regions of the MBL (Hercynian, hydrous); 5, veins related to Tertiary volcanism; 6, lower crust; 7, Tertiary intrusions (alkalic and/or tholeiitic); 8, middle and upper crust; 9, magma chamber (alkaline differentiates); 10, Vogelsberg.

Schematic representation of the components of the crust and mantle beneath the Vogelsberg - after Boggard and Wörner - reference in sources. 1, Upwelling asthenosphere (EAR - European Asthenospheric Reservoir - signature); 2, lower lithospheric mantle (depleted); 2a, metasomatized regions of the TBL (anhydrous); 3, hydrous mineral bearing veins (∼70 Ma?); 4, upper lithospheric mantle (depleted); 4a, metasomatized regions of the MBL (Hercynian, hydrous); 5, veins related to Tertiary volcanism; 6, lower crust; 7, Tertiary intrusions (alkalic and/or tholeiitic); 8, middle and upper crust; 9, magma chamber (alkaline differentiates); 10, Vogelsberg.

Volcanism of Vogelsberg was primarily effusive, with rift's eruptions. Nevertheless, most explosive Strombolian episodes, with emissions of ash and bombs, and more violent phreatomagmatic eruptions have also marked the massif.

At the cessation of the volcanic activity, there are 9-10 Ma, the action of the last glaciation and erosion weathering changed the topography. Basalts, harder, remained almost intact. The tuffs of slag have been eroded, except in areas of overlapping by basaltic rocks. Oxides of aluminum, iron and titanium have accumulated in places ... and degradation in tropical climate at the time, left laterite and bauxite.

On basaltic soils, hardwood settled, and beautiful forests of beech trees are grown on the hills. The lower areas are characterized by an agricultural landscape and hedges.

The region was known by the Romans as "Buchonia" ... the name called the Fulda region until the Middle Ages.


 

Amoeneburg, built on a basalt hill, north of the Vogelsberg - Staedte fotos.

Amoeneburg, built on a basalt hill, north of the Vogelsberg - Staedte fotos.

Before examining some volcanic spots in search of basalt and tuff, see the benefits left by this massive volcanic to locals.

Villages and towns are built on volcanic vents: Amoeneburg, Herbstein, Schotten. These mounds were previously provided strategic points.


 

Vogelsberg / Michelnau: barn with a basaltic basement - Photo Bernard Duyck 05.2014

Vogelsberg / Michelnau: barn with a basaltic basement - Photo Bernard Duyck 05.2014

Basalt was used as building material. Many villages once had their own small quarry  for producing stones for castle, the underbody of houses and farms, walls and bridges. Currently, they deliver pavers and gravel.

Iron ore was mined there until the 20th century, and enriched various villages. The few companies still active today import their raw materials.

Water is abundant in Upper Vogelsberg and basalt acts as a filter and tank: the rainwater seeps through fractures and stored over impermeable layers, then feed sources, which distribute the drinking water in all directions.

The fauna and flora also benefits. For centuries, courageous hand harvested and placed on property lines the basalt blocks, establishing walls allowing fauna to develop there and giving shelter to wildlife. On boulder fields, there are no less than 14 species of rare mosses.

 

Vogelsberg / Grebenhain: mosses cover the blocks of basanite of the "Bonifatiuskanzel" - photo Bernard Duyck 05.2014

Vogelsberg / Grebenhain: mosses cover the blocks of basanite of the "Bonifatiuskanzel" - photo Bernard Duyck 05.2014

Sources :

- Petrogenesis of basanitic to tholeiitic volcanic rocks from the Miocene Vogelsberg, Central Germany - by P.J.F. Bogaard & G. Wörner / Journal of Petrology.

- Der Vogelsberg - Geotope im grössten vulkangebiet mitteleuropas - Th. Reischmann & Ad. Schraft.

- DVG - Deutsche Vulkanologische Gesselschaft - Das vulkangebiet Vogelsberg - link

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

The Vogelsberg volcanic massif is located in the Rhine graben, a plain 35 km wide on average x 300 km. length, between Basel in the south and Frankfurt to the north.

The Rhine Graben forms the central segment of the European Cenozoic rift system that stretches over 1,000 km from the Mediterranean to the North Sea.

The opening of the Rhine graben began during the Tertiary (there are about 33 million years ago), at the beginning of the Oligocene. The gap formed is quickly invaded by the sea, first in conjunction with Alpine Ocean. It is deposited sediment in particular economic interest: sodium salts and potassium, also marl and sandstone where oil has accumulated (deposit Pechelbronn). The gap then opens into the North Sea. Then a regional tilting due to the uplift of the Alps causes the retreat of the sea and only freshwater lakes remain.

The Rhine Valley has all the geological characteristics of a continental rift:
- The Rhine Valley is located in intra-plate area.
- The presence of an axial sedimentary plain where sedimentation was very important.
- Curbs structured in "tilted blocks" by playing normal faults. This reflects a tectonic extension. The presence of these faults, mostly inactive, explains the existing residual seismicity in this area.
- An important volcanism but of alkaline type : there is no ocean floor that was put in place.
- A rise in the Moho at the origin of the crustal thinning and the birth of magmas.

 

Volcanic fields in central-western Europe: in the vicinity of Frankfurt, the Vogelsberg and Rhön - Eifel is referred WEVF (West Eifel volcanic field) HEVF (Hocheifel VF) EEVF (East Eifel VF) - map in "Volcanism" / H.U.Schmincke.

Volcanic fields in central-western Europe: in the vicinity of Frankfurt, the Vogelsberg and Rhön - Eifel is referred WEVF (West Eifel volcanic field) HEVF (Hocheifel VF) EEVF (East Eifel VF) - map in "Volcanism" / H.U.Schmincke.

The peri-alpine alkaline volcanism produced in Germany the massive of  Eifel, Vogelsberg and Rhön. The last two massive are dated from 20 to 14 Ma, a short time, geologically. (18-10 Ma Vogelsberg - pic 17-15 Ma)

Magmas issued have a composition ranging from basanite to quartz tholeiitic; from trace elements and isotopic composition of Nd, Sr and Pb, we deduce three different mantle sources:
- A source of a typical  asthenospheric plume enriched in trace elements, the composition similar to that of European asthenospheric tank in connection with the tertiary volcanic level.
- A depleted mantle source, located in the upper lithospheric mantle or the asthenosphere,
- A veined mantle source (marbled).

This suggests three stages of training:
1. Mixtures melt from the mantle back to the magma chamber and moving towards eruptions characterized by differentiated lavas.
2. Molten rocks from a depleted mantle source, and a progressive mixing with asthenospheric source.
3. After exhaustion of depleted mantle source, the molten rock are coming from an asthenospheric source.

 ... a shift towards sources less profound.

 

To the left, the Rhine Graben - doc.CNRS / C.Brunet - Jolivet & Nataf - to the right, ECVP (European Cenozoic Volcanic Province) subareas Vogelsberg - Age data from Abratis et al. - Click to enlarge. To the left, the Rhine Graben - doc.CNRS / C.Brunet - Jolivet & Nataf - to the right, ECVP (European Cenozoic Volcanic Province) subareas Vogelsberg - Age data from Abratis et al. - Click to enlarge.

To the left, the Rhine Graben - doc.CNRS / C.Brunet - Jolivet & Nataf - to the right, ECVP (European Cenozoic Volcanic Province) subareas Vogelsberg - Age data from Abratis et al. - Click to enlarge.

Location and assumed mechanism of implementation :

Areas of volcanism are located perpendicular to the rift system of the upper Rhine valley, oriented NNE-SSW.

The lithosphere has a uniform average thickness of 100 to 140 km. in the Western Europe and Central Europe. In contrast, this thickness is only 60 km. in the Rhenish Massif, in relation to the former Variscan welds. Crustal lithosphere has a thickness less than 30 km. under the Vogelsberg and is penetrated by numerous dykes at a depth of 20 km (Braun & Berckhemer 1993)

An uprising of the asthenosphere-lithosphere boundary could have been caused by a local thinning of the ductile lower crust under extension resulting from the subduction of the Alpine lower crust.

 

The peri-Alpine Tertiary volcanism (purple) - extensive areas of tectonic uplift induced by the Alps (shaded red) - Doc. by Bellon & Brousse / Aurelienb

The peri-Alpine Tertiary volcanism (purple) - extensive areas of tectonic uplift induced by the Alps (shaded red) - Doc. by Bellon & Brousse / Aurelienb

Geodynamic model proposed for the origin of the ECVP - Alpine subduction thinner crust at the welds Variques in the pre-Alps. Thinning allows asthenospheric ascent and movement of small-scale convection in the Rhine graben - doc. in "The European Cenozoic Volcanic Province is not Caused by mantle plumes" / by R.Meyer & G.Foulger

Geodynamic model proposed for the origin of the ECVP - Alpine subduction thinner crust at the welds Variques in the pre-Alps. Thinning allows asthenospheric ascent and movement of small-scale convection in the Rhine graben - doc. in "The European Cenozoic Volcanic Province is not Caused by mantle plumes" / by R.Meyer & G.Foulger

Sources :

- Eduterre : Un rift continental, le fossé Rhénan - link

- CNRS - Le fossé Rhénan, un océan avorté - link

- Petrogenesis of basanitic to tholeiitic volcanic rocks from the Miocene Vogelsberg, Central Germany - by P.J.F. Bogaard & G. Wörner / Journal of Petrology.

- Petrogenesis of tertiary continental intra-plate lavas from the Westerwald region, Germany  / Journal of Petrology.

- The European Cenozoic Volcanic Province is not caused by mantle plumes / by R.Meyer & G.Foulger

- Der Vogelsberg - Geotope im grössten vulkangebiet mitteleuropas - Th. Reischmann & Ad. Schraft.

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

A plateau with an average altitude of 1,220 meters occupies the south- west of Unimak Island. It could be the surface of a truncated and highly eroded ancestral cone , with steep slopes to the north and gentle slopes on the other sides .

Three volcanic structures are located: the Westdahl peak , Faris peak and Pogromni Peak volcano.


 

The uppermost zone of Westdahl : left, the Westdahl Peak , right, Faris Peak. The crack intersecting the summit ice cover from the top was formed at the beginning of the 1991-92 eruption , characterized by fountaining . Right center , the cinder cone of the eruption 1991-92 and his lava flows covered with snow. - CF Zeillemaker Photo / U.S. Fish & Wildlife Service / AVO

The uppermost zone of Westdahl : left, the Westdahl Peak , right, Faris Peak. The crack intersecting the summit ice cover from the top was formed at the beginning of the 1991-92 eruption , characterized by fountaining . Right center , the cinder cone of the eruption 1991-92 and his lava flows covered with snow. - CF Zeillemaker Photo / U.S. Fish & Wildlife Service / AVO

Topographic map Westdahl / Unimak island - doc AVO - USGS

Topographic map Westdahl / Unimak island - doc AVO - USGS

In the foreground, the Fisher caldera , with its rims not covered with snow, and left the Mt. Finch - In the left background, the snow-capped peaks , from left to right : Westdahl , Faris Peak, the Progromni and Pogromni sister - photo Peter Stellling 1998 / AVO - USGS

In the foreground, the Fisher caldera , with its rims not covered with snow, and left the Mt. Finch - In the left background, the snow-capped peaks , from left to right : Westdahl , Faris Peak, the Progromni and Pogromni sister - photo Peter Stellling 1998 / AVO - USGS

The Westdahl has a basal diameter of 18 km. His first historical eruption , of VEI 4, took place in 1795.

In 1991, a crack, 8 km long , has expanded from its peak on the east side of Westdahl (photo above ) . The eruption began on 29 November by a spectacular fountaining , and explosions, accompanied by a plume 6,000 meters high. Lava flows traveled 7 km . from the main vent , a cinder cone visible today, widening the low flanks.





 

Westdahl - December 4, 1991 - photo Kristina Neal / AVO - USGS

Westdahl - December 4, 1991 - photo Kristina Neal / AVO - USGS

Lava flows of Westdahl - 91-92 eruption - photo C.Dau 12.03.1992 / U.S. Fish & Wildlife Service / AVO

Lava flows of Westdahl - 91-92 eruption - photo C.Dau 12.03.1992 / U.S. Fish & Wildlife Service / AVO

The top of Westdahl and Faris Peak - photo Cyrus Read / AVO - USGS

The top of Westdahl and Faris Peak - photo Cyrus Read / AVO - USGS

The stratovolcano Pogromni , conical shape, is located 5 km. north of Westdahl . It rises to 2002 meters. Despite its taller , it is eroded by glaciers and presumed oldest , with activity in the late Pleistocene. All lavas from Pogromni are tholeiitic basalts .

Close to the latter , another top, Pogromni sister , 1.230 meters high , could be a remnant of an older vent.

Five monogenetic cinder cones are aligned with the Pogromni on a NW-SE axis . Their height is 50 to 100 meters and their surface heavily oxidized.


 

Volcano Pogromni -  Photo John Nickels / Unimak.us

Volcano Pogromni - Photo John Nickels / Unimak.us

Sources ;

 - AVO – Volcano information - link

- Volcanoes of North America: United States and Canada – by Charles A. Wood & Jürgen Kienle.

- Global Volcanism Program - Westdahl

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Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
The Isanotski or " Ragged Jack" - photo John Nickels / Unimak.us

The Isanotski or " Ragged Jack" - photo John Nickels / Unimak.us

The Isanotski stratovolcano , also known as the " Ragged Jack" , has an heavily eroded summit , consisting of rugged pinnacles, and covered with glaciers.

Four historical eruptions were recorded in the 18 and 19 centuries , poorly documented , and considered by the GVP as uncertain , given the state of extreme erosion of the summit. They are probably due to its neighbor, Shishaldin .

 

The top of the Isanotski , and in the cut , the symmetric Shishaldin - photo Cyrus Read / AVO - USGS

The top of the Isanotski , and in the cut , the symmetric Shishaldin - photo Cyrus Read / AVO - USGS

Located between Isanotski and Roundtop , a Pleistocene volcano , called Unimak 5270 , is considered a volcano, or a vent in part, due to aerial observations showing radial lava flows from the top ( Chris Nye, 2008)

Shishaldin , Isanotski and Roundtop - Map U.S. Geological Survey Andalkar Amar / AVO - USGS

Shishaldin , Isanotski and Roundtop - Map U.S. Geological Survey Andalkar Amar / AVO - USGS

The Fisher Caldera , 18 km. on 11 , features three lakes and several cinder cones and spatter cones , including the Mount Finch, a central composite cone of over 2000 m. in diameter and 400 m high. It is the largest of 12 calderas formed in Alaska during the Holocene .
 

Fisher caldera , and the silhouette of Shishaldin - photo John Nickels / Unimak.us

Fisher caldera , and the silhouette of Shishaldin - photo John Nickels / Unimak.us

A 2004 study considers that the volcanic system , before the eruption forming the caldera  9400 years ago , consisted of a group of three small stratocones , independently in activity between 66,000 and 9400 years ago.

The caldera was formed during a single eruption , producing a thick deposit of dacitic ash , two deposits of pyroclastic flows , a small dacitic flow and a mixed basalt - dacite flow . Pyroclastic flows , particularly mobile , have reached the Bering Sea , to 15 km , and the Pacific Ocean to 8 km. , overcoming reliefs of more than 400 m.

A lake was then filled much of the caldera during a rest period .

Volcanic activity resumed at the start of intra- calderic vents , producing fallout of thick slag interbedded with lacustrine sediments. Several stratocones have developed, which one is marked by a collapse . The caldera lake was drained abruptly when a phreatomagmatic eruption produced a wave that incised and topped the south wall of the caldera. Deposits containing accretionned lapilli, found inside and outside the caldera, reflect the phreatomagmatic activity in Holocène .

A small explosive eruption is dated 1826 ; current activity is hydrothermal , with low temperature fumaroles on the western flank of Mount Finch . Turquoise Lake , at the base of the cone Finch , emit hydrogen sulphide .

 

The Shishaldin and caldera Fisher - 14/05/2014 Photo / NASA / USGS Landsat Earth explore by 8 OLI

The Shishaldin and caldera Fisher - 14/05/2014 Photo / NASA / USGS Landsat Earth explore by 8 OLI

On the left, the caldera Fisher - Catalog of the Historically active volcanoes of Alaska - Miller and others (1998 ) and Miller and Smith (1977)  - to the right , radar image of Unimak Island -  Oregonstate University - a click to enlarge .On the left, the caldera Fisher - Catalog of the Historically active volcanoes of Alaska - Miller and others (1998 ) and Miller and Smith (1977)  - to the right , radar image of Unimak Island -  Oregonstate University - a click to enlarge .

On the left, the caldera Fisher - Catalog of the Historically active volcanoes of Alaska - Miller and others (1998 ) and Miller and Smith (1977) - to the right , radar image of Unimak Island - Oregonstate University - a click to enlarge .

Sources :

- AVO - Volcano information - link

- Eruptive history of Fisher Caldera, Alaska, USA by Pete Stelling & al.- link

- Global Volcanism Program - Isanotski

- Global Vocanism Program - Fisher

- Unimak Landforms

- Catalog of the historically active volcanoes of Alaska

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