Overblog
Suivre ce blog Administration + Créer mon blog

Earth of fire

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

Articles avec #excursions et voyages catégorie

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

The gorge of the Columbia River in the northwestern United States, as one of its extraordinary landscapes, born of past cataclysmic events.

This canyon, deep over 1,200 meters, extends over 130 km.from the confluence of the Deschutes River to that of the Sandy River. The gorge intersects the Cascades Range, providing the only waterway between the plateau of the Columbia River and the Pacific Ocean.

Columbia River Gorge - photo Linda Garrison / About geology.

Columbia River Gorge - photo Linda Garrison / About geology.

Location of the Columbia river gorge in relation to the Columbia River Basalt Group, in the western of the United States, intersecting the volcanic Cascade Range.

Location of the Columbia river gorge in relation to the Columbia River Basalt Group, in the western of the United States, intersecting the volcanic Cascade Range.

Its history is first intertwined with the flood basalt of CRBG / the Columbia River Basalt Group.

This basalt province is the youngest, smallest and best-preserved terrestrial basalt provinces, covering 210,000 km² between the states of Oregon, Washington, Idaho, and northern Nevada.

It was formed when massive fissure effusive eruptions, fed by the magma from a mantle plume, and after more than 350 lava flows between 16.7 and 5.5 Ma. The majority of the basalt (93%) was issued only in about 1.1 Ma, between 16.7 and 15.6 Ma. Some 240 million cubic meters of lava have spread, moving on hundreds of kilometers from the vent issuer, and crossing the path of the arc volcanic Cascades.

On the left, the Columbia River Flood-basalt province - doc.Victor Camp & Martin Ros - right, the extension of large basalt formations - doc.Reidel et al. 2002 - A click to enlarge the maps. On the left, the Columbia River Flood-basalt province - doc.Victor Camp & Martin Ros - right, the extension of large basalt formations - doc.Reidel et al. 2002 - A click to enlarge the maps.

On the left, the Columbia River Flood-basalt province - doc.Victor Camp & Martin Ros - right, the extension of large basalt formations - doc.Reidel et al. 2002 - A click to enlarge the maps.

Stratigraphic subdivisions of CRBG and their ages - Doc. USGS

Stratigraphic subdivisions of CRBG and their ages - Doc. USGS

Following this era of volcanism at the end of the last glaciation, the waters of the great lake Missoula and the Columbia Lake broke their ice dams containing them repeatedly, causing major floods - floods called Spokane, or Brest , or Missoula floods (dated between 15.000 and 13.000 years ago).

The waters have washed away chunks of ice, granite and shale through the Columbia River Basin, and carved in the way the landscape of the gorge. The widening of the canyon caused the cascade of adjacent rivers in their race to the Pacific Ocean. This brutal episode of erosion, adding to the natural erosion of the river has exposed many layers of volcanic rock ... as shown in the picture taken from Rowena Crest Viewpoint, below.

 

Columbia River Gorge - layering of basalt, from Rowena Crest Viewpoint view - photo Liz Westby 2014 / USGS - CVO

Columbia River Gorge - layering of basalt, from Rowena Crest Viewpoint view - photo Liz Westby 2014 / USGS - CVO

The gorge of the Columbia river, to Crown Point, the point reached by the Missoula floods - HUX photo.

The gorge of the Columbia river, to Crown Point, the point reached by the Missoula floods - HUX photo.

Missoula and Columbia lakes, icecaps and the area inundated by the Missoula Floods  - USGS map

Missoula and Columbia lakes, icecaps and the area inundated by the Missoula Floods - USGS map

The gorge has been inhabited for over 13,000 years and has seen the passage of the Marmes and Folsom peoples, from Asia through the Bering Strait, according to archaeological discoveries.

It served as a transportation corridor over thousands of years, borrowed by the first native peoples and the Lewis and Clark Expedition (1805-1806) to reach the Pacific ... and then by the steamboat and the train before the roads and highways.

Map of Lewis & Clark expedition (1805-1806) in the American West - Doc. USGS

Map of Lewis & Clark expedition (1805-1806) in the American West - Doc. USGS

To follow, the Oneonta Gorge, and the unique ecosystem of the Columbia river gorge.

 

Sources :

- USGS - Cascade Volcano Observatory - Columbia River Basalt Group Stretches from Oregon to Idaho - link

- Ice Age Flood Institute  - About the Ice Age floods - link

- USGS - CVO - The Cordilleran Ice sheet and Missoula Floods  - link

Lire la suite

Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
 Ben Nevis - photo wikipedia

Ben Nevis - photo wikipedia

Distribution of plutonic rocks (pink) and volcanic rocks (blue) - Ben Nevis, No. 1 - Glen Coe, No. 2. - doc. Jgs / Lyell Collection

Distribution of plutonic rocks (pink) and volcanic rocks (blue) - Ben Nevis, No. 1 - Glen Coe, No. 2. - doc. Jgs / Lyell Collection

At some distance from Glen Coe, Ben Nevis is another example of a giant caldera dating from 350 Ma.

Ben Nevis, Beinn Nibheis in Gaelic meaning malicious mountain, with 1,344 m., is the highest point in Scotland and a place renowned for climbing.

Nevis massif consists of a mixture of different colors of granite, cooled thoroughly, and of black lava, which spread on the surface.

Schematic formation of the caldera of Ben Nevis - the current level after erosion is marked by the black line - Doc. Geocaching.

Schematic formation of the caldera of Ben Nevis - the current level after erosion is marked by the black line - Doc. Geocaching.

Ben Nevis, facing south - photo Blisco.

Ben Nevis, facing south - photo Blisco.

Research has shown that the Devonian's igneous rocks form concentric intrusions in circular dykes in the surrounding shales.

The inner ring, known as "inner granite", is the most southern part of the mountain above Lochan Meall year t-Suidhe and the ridge of Mòr Dearg Càrn.
External granites / "Outer granite" are more reddish.
Both granites are set up to thousands or even millions of years apart.

The summit dome itself is composed of andesite and basaltic lava, that covered the landscape before the collapse of the caldera. (See diagram)

The whole was then heavily eroded by glaciation.


 

Ben Nevis and Mòr Dearg Càrn - photo Planetware

Ben Nevis and Mòr Dearg Càrn - photo Planetware

Glen Coe and Ben Nevis are sites of special scientific interest, and have the status of Special area of Conservation.

 

Sources :

- Timing, relations and cause of plutonic and volcanic activity of the Siluro-Devonian post-collision magmatic episode in the Grampian Terrane, Scotland - by J.C.Neilson & oth.- link

- The Edinburgh geologist / issue n°43 / Mountain geology - link

- British Geological Survey - Glen Coe & Ben Nevis

Lire la suite

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

Forming one of the most spectacular scenery in Scotland, Glen Coe is a glen - a long glacial valley in U shaped - of volcanic origin.

Geologically spoken, Glen Coe is formed by the remnants of a caldera of a large ancient and extinct volcano.

The rocks found in Glen Coe, including those of volcanic origin, reflect the different environments during their formation : a medium shallow sea, or a subtropical desert environment, some rolled under a thick ice cover.
 

Glen Coe in the Scottish Highlands... the remains of a volcanic caldera

Glen Coe in the Scottish Highlands... the remains of a volcanic caldera

Tectonic Evolution from Ordovician to Devonian - on the map of the left is the current UK into two entities yet separated.

Tectonic Evolution from Ordovician to Devonian - on the map of the left is the current UK into two entities yet separated.

Around 470 to 460 Ma, the ancient continents, called Laurentia, Baltica and Avalonia, collided ... at that time, violent tectonic movements initiates the Caledonian mountain building.

There are 420 Ma, Glen Coe has experienced a period of cataclysmic volcanic activity, during which five major eruptions are counted. Each eruption mobilizing thousands of cubic kilometers of magma from the volcano Glen Coe ; each time, emptying of the magma chamber causes the collapse of the volcano and the formation of a caldera.

Glen Coe - a glen, a glacial valley in U shaped - photo Gil Cavalcanti

Glen Coe - a glen, a glacial valley in U shaped - photo Gil Cavalcanti

To the cessation of volcanic activity, the magma is squeezed into the cracks where it solidified to form a ring intrusion, surrounding currently the volcanic rocks.

For millions of years, the erosion by the elements, ice, wind and rain, have exposed these volcanic rocks formed millions of years before. The last glaciation, about 10,000 years ago, left a glacial valley in a U-shaped

 

"Glen Coe, Looking North" - Catriona Herd canvas - 120 x 76 cm - Doc. Artpistol

"Glen Coe, Looking North" - Catriona Herd canvas - 120 x 76 cm - Doc. Artpistol

The place is unfortunately also known for the "massacre of Glen Coe" ,which took place on February 13, 1692, at the time of the Glorious Revolution, also called wrongly the Bloodless Revolution.

The massacre began simultaneously in three locations in Glen Coe, before spreading to the entire valley. Thirty-eight men from the clan Mac Donald were killed by those to whom they had given hospitality ... Forty women and children died of exposure after a fire in their home. The hundred twenty assassins troop was sent by Guillame III, Prince of Orange.

 

Source :

Lochaber geopark - link

Lire la suite

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

Southwest of previous volcanic fields, the Red Hills volcanic field consists of young volcanic structures, surrounded by mesas capped with basalt, and located near the border with Arizona and Springerville field.


 

 Red Hill cone and lava flows - Nasa via Larry crumpler Photo

Red Hill cone and lava flows - Nasa via Larry crumpler Photo

The maar Red Hill:

Red Hill cone, formed of red cinder is morphologically altered more than other basaltic cones dating from 300,000 years of Springerville field, and less than those dated of 800,000 years ... which gives it an age of about 500,000 years.

Major lava flows associated are olivine basalts, with Pressures ridges.

The maar Red Hill is an example of a maar associated with faults and a fissure volcanic activity. The maar and a small elongated to the south vent are aligned parallel to the fault scarps involving a stress different of the Springerville field.

A small cinder cone occupies the floor of the maar. The ash, interbedded with deposits of maar beds, suggest a departure from the eruption with ash and pyroclastic activity occurring, which has evolved to more explosive eruptions of maar type, then return to the primitive type.

 

Red Hill volcanic field - Red Hill cone - photo L.Crumpler / NMM

Red Hill volcanic field - Red Hill cone - photo L.Crumpler / NMM

The maar of Zuni Salt Lake is part of a complex of cones and maars aligned on a fracture zone of 60 km. The lake is about 1,895 m. high.
 

The Zuni Salt Lake maar and three basaltic cinder cones - photo Larry Crumpler / NMM

The Zuni Salt Lake maar and three basaltic cinder cones - photo Larry Crumpler / NMM

Map of Zuni Salt Lake - doc. GGI

Map of Zuni Salt Lake - doc. GGI

Cross section of Zuni Salt Lake - Doc. GGI

Cross section of Zuni Salt Lake - Doc. GGI

Beautiful photos of maar on:http://www.airphotona.com/image.asp?imageid=4031

A period of surtseyan activity with continuous phreatomagmatic surges, which established a tuff ring; ash particles are highly altered in palagonite, and the presence of accetionned lapilli is observed. It was followed by intermittent Strombolian explosions and ash deposits found up to 8 km. of the salt Lake. Finally, building a cinder cone is explained by the introduction of a basaltic dyke ring that accessed the surface to give spatter and short lava flows. Maar subsidence occurred during the eruption, and the edge of the crater was at the end of the eruption at 30 meters above the surrounding terrain. The climate,  wettest at the eruption time, allowed the crater to fill; diatoms, ostracods and gastropods have been dated  by C14 to 22,900 + / - 1400 years.

The climate is then dried by reducing the area of the lake by a third, and is home of  bacteria, algae and crustaceans Artemisia salina.

The Indians used the salt for at least 1,000 years, and in modern times, it was harvested for animal use, metallurgy, and road salting.

 

Sources :

- New Mexico museum of natural history and sciences - Red Hill volcanic field  - link

- Quaternary basalt fields of west-centralNew Mexico … Zuni canyon aa flow, Zuni Salt lake maar – by W.E.Elston & K.H.Wohletz - link

Lire la suite

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

South of Albuquerque, some volcanic fields and underground structure are interesting.

The Lucero volcanic field:

Cerro Verde, one of the youngest volcanic centers, is a classic basaltic shield volcano. It has fueled long lava flows of 42 km., which are preserved along the Rio San José, a "modern" tributary of  Rio Puerco and Rio Grande.

 Lucero volcanic field - Cerro Verde - Larry Crumpler Photo / NMM

Lucero volcanic field - Cerro Verde - Larry Crumpler Photo / NMM

A cone of slag, the Cerro Colorado, also called "Volcano Hill", is located in the volcanic field near the Cerro Verde.

Streams of older lava cover the mesas, including Black Mesa, east of the volcanic field, and the western border of monoclinal dip of the Rio Grande rift.

Lucero volcanic field - Cerro Colorado - Larry Crumpler Photo / NMM

Lucero volcanic field - Cerro Colorado - Larry Crumpler Photo / NMM

Map of Albuquerque basin and position of the Lucero volcanic field and Socorro magma body - map NMM

Map of Albuquerque basin and position of the Lucero volcanic field and Socorro magma body - map NMM

The Socorro magma body:

This magma body is located at a depth of 19 km., far from the surface ... but monitored by geologists, in this highly seismic zone.

Geophysical data suggest the presence of a magma body as a Laccolith (*) in the middle crust beneath the Rio Grande rift. Its volume is estimated at several thousand cubic kiomètres.

Surveillance by radar interferomerty gives elevations 2.5mm / year on average (2-4 mm / year between 1992 and 2000). Affected area by the lifting is approximately 7,000 square kilometers; the maximum lift near the center of the area reaches twenty centimeters from the periphery.

Socorro magma body - left, extension and diagram of magmatic body / doc NMM - right, crustal uplift due of the inflation of the Socorro magma body / doc. http://sioviz.ucsd.edu - one click to enlarge Socorro magma body - left, extension and diagram of magmatic body / doc NMM - right, crustal uplift due of the inflation of the Socorro magma body / doc. http://sioviz.ucsd.edu - one click to enlarge

Socorro magma body - left, extension and diagram of magmatic body / doc NMM - right, crustal uplift due of the inflation of the Socorro magma body / doc. http://sioviz.ucsd.edu - one click to enlarge

Socorro magma body - revealed by radar interferometry and seismology - Fialko & Simmons 2001

Socorro magma body - revealed by radar interferometry and seismology - Fialko & Simmons 2001

Topographic analyzes show no uprising in the long term in Rio Puerco and Rio Salado, nor for old alluvial surfaces, contrary to the evidence of an uprising in the last centuries ... which means that magma body is young.

Recent modeling indicates that the lifting of the Socorro magma body is due to a viscoelastic response of the crust around it. The implementation of this magmatic Laccolith over millions of years would not be in time relationship with the surface uplift

This hot magma body may, in the future, cause the melting of the surrounding rock, and even lead to an eruption of rhyolite viscous magma.

View of the Socorro magma body (red), local microearthquakes (circles; 1975–1995) and land surface. The example local earthquake seismogram (yellow) shows strong seismic reflections (PzP, SzS) from the nearly flat upper surface of the body.

View of the Socorro magma body (red), local microearthquakes (circles; 1975–1995) and land surface. The example local earthquake seismogram (yellow) shows strong seismic reflections (PzP, SzS) from the nearly flat upper surface of the body.

(*) Laccolith: mass of intrusive rocks, bulging at the top, creeping into a sedimentary series.

 

Sources :

 - AGU - Geophysical evidence for a magma body in the crust in the vicinity of Socorro - by A.R.Sanford  - link

- Caltech - Evidence for on-going inflation of the Socorro Magma Body, New Mexico, from interferometric synthetic aperture radar imaging - Fialko, Yuri and Simons, Mark (2001) – link

- New Mexico Geological Society Guidebook, 34th Field Conference, Socorro Region II, 1983 - Magma bodies in the Rio Grande rift in central New Mexico - A.Sanford - link

- New Mexico Museum of Natural history – Soccoro active magma body – link

- Effects of Active Faults on Probabilistic Seismic Hazard Estimates for the Socorro Area Using Instrumental Data 1962 through 1995 - link

Lire la suite

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

The West Mesa regio is located west of the city of Albuquerque, in the middle of the rift valley of the Rio Grande. The Rio Grande rift valley is one of the few active air rifts, such as the Great East African Rift, the Rhine Graben and the rift Lake Baikal in Russia.

This area of ​​weakness and stretching of the crust promoted the formation of numerous cracks through which the magma has found ways to rise to the surface.

 

Albuquerque volcanic field - photo Larry Crumpler - NMM

Albuquerque volcanic field - photo Larry Crumpler - NMM

Over a length of 8 km., 150,000 years ago, the fissure eruptions formed curtains of fire, as in Hawaii, and are responsible for six lava flows that covered the Santa Fe Formation, an accumulation of gravel and sand.

The first two additions, the most important, created the lava plateau of West Mesa. With the cooling of the lava flows, the cracks are blocked, and the residual lava has formed cinder and spatter cones. Three cones are most important and prominent on the western edge of the site ... they are known as the Three Sisters: Vulcan, Black and JA volcanoes.

Particularly visible in the cone Vulcan, an asymmetry of the cone is noticed due to the wind direction at the time of the eruption. The crater of Vulcan contains a small lake of basaltic  solidified lava,  with underdeveloped colonnades. Sinuous lava tubes are preserved on the NE & NW flanks of the cone.

 

The six lava flows and the position of cones and petroglyph sites - one click to "Lighten" the legends - Doc. Geology from Connell (2008) ./ http://geoinfo.nmt.edu/tour/federal/monuments/petroglyphs/map_abq_volcanoes.pdf

The six lava flows and the position of cones and petroglyph sites - one click to "Lighten" the legends - Doc. Geology from Connell (2008) ./ http://geoinfo.nmt.edu/tour/federal/monuments/petroglyphs/map_abq_volcanoes.pdf

Petroglyh NM - the Thress sisters : Black, JA and Vulcan volcanoes - photo American southwest

Petroglyh NM - the Thress sisters : Black, JA and Vulcan volcanoes - photo American southwest

Left, JA volcano - right, Black volcano - one click to enlarge - photos Michaelh2001Left, JA volcano - right, Black volcano - one click to enlarge - photos Michaelh2001

Left, JA volcano - right, Black volcano - one click to enlarge - photos Michaelh2001

Erosion by wind and rain over thousands of years of the Santa Fe undermying Formation
, more friable and therefore faster than the basalt layer surmounting, removed a significant portion of material. the basaltic layer private of support  broke and collapsed in large blocks forming the current escarpment.

 Formation  of West Mesa and of the boulders of Petroglyph NM - NPS schemes -. one click to a separate vision. Formation  of West Mesa and of the boulders of Petroglyph NM - NPS schemes -. one click to a separate vision. Formation  of West Mesa and of the boulders of Petroglyph NM - NPS schemes -. one click to a separate vision.

Formation of West Mesa and of the boulders of Petroglyph NM - NPS schemes -. one click to a separate vision.

The Petroglyph National Monument:

The boulders were used by the native and mestizo populations with the Mexicans and Spaniards for the realization of more than 24,000 petroglyphs, mostly dating from ancestral Pueblo period, between 1300 and 1600.

That's the nature of basalt blocks that made visible these petroglyphs. Basalt, gray originally, discolored following an oxidation phenomena ... The high content of iron, manganese and calcium allowed, following exposure to oxygen and the water, the formation of  a dark patina on the surface, called the "desert varnish."

Petroglyphs in a basalt boulder in Rinconada Canyon - photo american southwest

Petroglyphs in a basalt boulder in Rinconada Canyon - photo american southwest

Petroglyphs - photo american southwest

Petroglyphs - photo american southwest

New Mexico - 5 - West Mesa and Petroglyph National Monument.

The engraving of the blocks highlighted these intricate designs, depicting scenes of hunting, animals, humans, masks and other geometric shapes, by scraping the varnish layer. They had a cultural and spiritual significance to the original inhabitants and retain a great value for their descendants.

They are grouped in three main canyons, the Rinconada, Boca Negra and Piedras Marcadas canyons, grouped in Petroglyph National Monument, recently established in 1990.

A "star character" in Rinconada section of Petroglyph NM - photo Jerry Willis

A "star character" in Rinconada section of Petroglyph NM - photo Jerry Willis

Sources :

- NPS – Petroglyph National Monument – link

- New Mexico bureau of geology and mineral resoources – link

- American Southwest - Petroglyph National Monument - link

Lire la suite

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

The Valles Caldera, 20-24 km wide., was formed following two large eruptions that created the plateau, called Bandelier Tuff. Before the collapse of the caldera, no great volcano was there ... only a few volcanoes dotted the region.

New Mexico-Valles Caldera - photo sat. Jesse Allen and Robert Simmon - NASA Earth Observatory

New Mexico-Valles Caldera - photo sat. Jesse Allen and Robert Simmon - NASA Earth Observatory

Digital 3D elevation of the Valles-Toledo complex, with boundaries of the calderas and internal post-caldera structures - Doc. New Mexico Museum of Natural History and Science

Digital 3D elevation of the Valles-Toledo complex, with boundaries of the calderas and internal post-caldera structures - Doc. New Mexico Museum of Natural History and Science

The Bandelier Tuff :

This rhyolite formation in Jemez mountain consists of deposits from two eruptions:
- The lower unit corresponds to the formation of the caldera Toledo, there are 1.45 Ma - volume 400 cubic km;
- the upper unit corresponds to the Valles Caldera, there are 1.1 Ma - volume 250 cubic km.

The formation begins when a mass of granitic magma rich in water about 1 million cubic kilometers rises to the surface. Arriving near the surface, it breaks the rocks which overcomes creating fractures in a circle.

When the eruption occurs, the water in the magma vaporizes and sprays the magma in thick clouds of ash and steam. These ignimbrites are deposited in all directions to form the Bandelier Tuff. The issuance of this huge volume empty the magma chamber, causing the collapse of a large caldera of 20-24 km. wide and 300 meters deep.

Above, the simplified geological evolution of the Valles Caldera - bottom, the volume compared of the Valles Caldera eruption compared to other major eruptions - one click to enlarge - diagrams New Mexico Museum of Natural History and Science
Above, the simplified geological evolution of the Valles Caldera - bottom, the volume compared of the Valles Caldera eruption compared to other major eruptions - one click to enlarge - diagrams New Mexico Museum of Natural History and Science

Above, the simplified geological evolution of the Valles Caldera - bottom, the volume compared of the Valles Caldera eruption compared to other major eruptions - one click to enlarge - diagrams New Mexico Museum of Natural History and Science

The Bandelier Ashflow tuff overcomes the red rocks of Permian - Larry Crumpler Photo / New Mexico Museum of Natural History and Science

The Bandelier Ashflow tuff overcomes the red rocks of Permian - Larry Crumpler Photo / New Mexico Museum of Natural History and Science

Bandelier Tuff Ash Flow - wall in Rendija Canyon near Los Alamos. - Photo L.Crumpler / New Mexico Museum of Natural History and Science.

Bandelier Tuff Ash Flow - wall in Rendija Canyon near Los Alamos. - Photo L.Crumpler / New Mexico Museum of Natural History and Science.

Rainwater and ice melt fill the caldera, to give a steaming sulphurous lake, because the eruption is still ongoing.


The post-caldera volcanism continues with the introduction of
- Lava domes located on the schematic map, from right to left anticlockwise, on circular fractures, and settled there 1Ma ( Cerro del abrigo and Media), 900,000 years (Cerro de Trasquilar), 800,000 years (Cerro Seco and San Louis) and 530,000 years (Mt. San Antonio)
- and a lifting of the floor of the caldera, with the formation of Redondo Peak, a resurgent dome. Crescent, the dome resurgence breaks and splits, forming cracks.

There are about 500,000 years, the caldera lake empties abruptly through the canyon of San Diego to the south, likely following the erosion of the ancestral Jemez River combined with the undermining due to hydrothermal phenomena. The dam failure decreases the amount of water available and hydrothermal events dimmed, especially as the magma chamber begins to cool.


 

Valles Caldera: Different domes, Redondo Peak resurgent dome and depression of Valle Grande

Valles Caldera: Different domes, Redondo Peak resurgent dome and depression of Valle Grande

New Mexico - 3 - the Valles-Toledo calderic complex.
Valles Caldera - Battleship Rock ignimbrite, structure left to SW by the draining of the caldera lake (see map above) - photo Ronda

Valles Caldera - Battleship Rock ignimbrite, structure left to SW by the draining of the caldera lake (see map above) - photo Ronda

Valles Caldera - "Soda Dam," dam on the Jemez River SW of the caldera - photo Lee Siebert

Valles Caldera - "Soda Dam," dam on the Jemez River SW of the caldera - photo Lee Siebert

The tuff, eroded by wind and rain, left cavities in the walls of canyons. These holes were used by the ancestral Pueblo people as living quarters and as building materials

... to see tomorrow.

 

Sources :

-  New Mexico Museum of Natural History and Science. - Valles caldeira / Jemez volcanic field

- The Bandelier Tuff: A study of ash-flow eruption cycles from zoned Magma Chambers - By R. L. Smith, R. A. Bailey

Lire la suite

Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Tectonic and location of the volcanic fields on the Jelez lineament, near Albuquerque.

Tectonic and location of the volcanic fields on the Jelez lineament, near Albuquerque.

On the alignment Jemez and north of Zuni-Bandera volcanic field, Mount Taylor is a conglomeration of several volcanic centers compounds by different magma.

Its symmetrical structure is the result of the accumulation of thick, sticky trachydacitic lava flows, then trachyandesitic, over traces of ancient rhyolitic eruptions, complemented by an outside apron
radiating of debris from the domes, mixed with pyroclastic materials.

The Mt.Taylor seen from Sandstone Bluffs Overlook / El Malpais - Larry Crumpler Photo / New Mexico Museum of Natural History and Science.

The Mt.Taylor seen from Sandstone Bluffs Overlook / El Malpais - Larry Crumpler Photo / New Mexico Museum of Natural History and Science.

Geological map of Mount Taylor - location of the different type of lava - Doc. NMM / L.Crumpler & F.Goff

Geological map of Mount Taylor - location of the different type of lava - Doc. NMM / L.Crumpler & F.Goff

Topography of Mt Taylor - photo Nasa / New Mexico Museum of Natural History and Science.

Topography of Mt Taylor - photo Nasa / New Mexico Museum of Natural History and Science.

Mount Taylor - Photo taken by Dr. Larry Crumpler / New Mexico Museum of Natural History and Science.

Mount Taylor - Photo taken by Dr. Larry Crumpler / New Mexico Museum of Natural History and Science.

Radial dikes of trachyandesites in the summit amphitheater represent feeder dykes of many viscous intrusions.

A pyroclastic cone could have enthroned in the central part animated of this
extrusive activity; he contributed to the production of materials that cover the lower slopes of the volcano of little colored fine ash and wide size blocks of trachydacite ... the final explosive activity and erosion have played a key role in the destruction of the summit.

Remains today a truncated cone, centered on the head of Water Canyon in a valley in amphitheater, with east, the peak of Mount Taylor and peak La Mosca.

Various hypotheses are scaffolded on the original height of Mount Taylor ... with as result, the average score elevation of around 4,000 meters.

Mt Taylor , seen from the north-west of Interstate 40 near Mesita - photo NMM

Mt Taylor , seen from the north-west of Interstate 40 near Mesita - photo NMM

Mt Taylor cross section, seen from the south - doc.Lipman & Mehnert 1980

Mt Taylor cross section, seen from the south - doc.Lipman & Mehnert 1980

Sources :

- New Mexico museum of Natural History and Science - Mount Taylor volcanic field - link

- New Mexico volcanoes - Plate tectonic.narod.ru - link

Lire la suite

Publié le par Bernard Duyck
Publié dans : #Excursions et voyages
Crater of the cinder cone Bandera - Larry Crumpler Photo / New Mexico Museum of Natural History and Science

Crater of the cinder cone Bandera - Larry Crumpler Photo / New Mexico Museum of Natural History and Science

Moreover El Malpais, the Zuni-Bandera volcanic field, located in New Mexico / USA, has seen many basaltic eruptions over millions of years.

The different lava flows, pahoehoe and aa, are differentiated by different shades of gray on the satellite photo, transcribed in different colors on the geological map.

Zuni-Bandera volcanic field - photo Landsat 8 / Nasa

Zuni-Bandera volcanic field - photo Landsat 8 / Nasa

  Geological Map of the Zuni-Bandera volcanic field -  Bandera flow in pink -  McCartys flow in red .

Geological Map of the Zuni-Bandera volcanic field - Bandera flow in pink - McCartys flow in red .

On the geochemical level, the flows of the Zuni-Bandera VF include tholeiitic basalts, alkaline basalts, andesites and basanites. They are considered as typical of intra-plate volcanism and chemical signatures have characteristics of enriched and impoverished mantle sources.

Among the lava flows, we examine the McCartys and Bandera Crater flow.

McCartys lava flow :

The McCartys lava flow comes from a low shield volcano, topped by a tiny cinder cone, 8 meters high.

Although some of the lava has flowed to the southwest of 8-9 km, most of it followed the existing drainage and sunk north for 40 km before turning east into the valley Rio San José. She covers ancient basalt and alluvium.

Dating, based in the 40s on Indian legends and archaeological evidence, and fixed after the year 700, was reviewed by radiocarbon datation between 2970 and 3010 before today, then technical He3 and CL36 gave an age between 2,500 and 3,900 years (Laughlin et al, 1994; Phillips et al, 1997.).


 

Zuni-Bandera VF - McCartys vent - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

Zuni-Bandera VF - McCartys vent - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

Zuni-Bandera VF -  McCartys pahoehoe sheet flows- photo www.psi.edu/pgwg/images/Oct11Image.html

Zuni-Bandera VF - McCartys pahoehoe sheet flows- photo www.psi.edu/pgwg/images/Oct11Image.html

Zuni-Bandera volc. field - Inflation pits in the McCartys flow - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

Zuni-Bandera volc. field - Inflation pits in the McCartys flow - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

Zuni-Bandera volc. field - Crevasse in the McCartys flow - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

Zuni-Bandera volc. field - Crevasse in the McCartys flow - photo Larry Crumpler / New Mexico Museum of Natural History and Science.

The Bandera flow :

It was produced by the Bandera Crater, a dual cinder cone, 150 meters high and 1,000 meters in diameter, breached southwest side as other cones volcanic field, in part as a result of winds that availed at the eruption time. A large lava tube, collapsed in places, extends to 29 km. south of the crater.

Seven steps have been recognized in the development of Bandera Crater and its associated flows, with the highlight being the eruption of black ash covering the cinder cone and the hills to the north. In the latter, two wells were opened in the ash of the hills for commercial purposes. Is it founded mantle xénolythes and megacrysts of anorthoclase. The lavas are nepheline, holocrystalline and vesicular.

Dating by various methods revealed that the ash and lava are dated there about 10,000 years.

Basalt casting Bandera was used as a building material by past civilizations, a.o. by the Anasazi Indians.

 

Zuni-Bandera volc. field - Lava chanel into an a-a lava flow from the crater Bandera - Larry Crumpler Photo / New Mexico Museum of Natural History and Science.

Zuni-Bandera volc. field - Lava chanel into an a-a lava flow from the crater Bandera - Larry Crumpler Photo / New Mexico Museum of Natural History and Science.

Zuni-Bandera volc. field - an Anasazi ruin consists of blocks of lava from the Bandera crater - photo geoinfo.nmt.edu

Zuni-Bandera volc. field - an Anasazi ruin consists of blocks of lava from the Bandera crater - photo geoinfo.nmt.edu

Sources :

- New Mexico museum of Natural History and Science - Zuni-Bandera volcanic field - link

- New Mexico bureau of geology & mineral resources –Zuni-Bandera Volc. Field / Geologic background - link

- New Mexico volcanoes - Plate tectonic.narod.ru - link

Lire la suite

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

After an interruption due to the volcanic news, return to the Sporades series ...

Kiritimati, also called Christmas Island, is a coral atoll in the equatorial Sporades.

This atoll has the largest land area of all listed atolls, with about 388 square kilometers. Its lagoon, open to the ocean northwest, has a size of the same order of magnitude ... difficult to quantify, due to its constant evolution : the main lagoon gradually transforms into a network of subsidiary lagoons, hypersaline ponds and salt marshes.

In addition to the main island, there are Cook island, dividing the input channel into two parts, and motus / islets located in the lagoon. The highest point rises to 13 meters above the sea level at Joe's Hill.

Kiritimati Island / Line islands - photo NASA ISS exp.4

Kiritimati Island / Line islands - photo NASA ISS exp.4

Navy Map of Christmas Island, to the left - compare with the land surface on the card to the right a click to enlarge .Navy Map of Christmas Island, to the left - compare with the land surface on the card to the right a click to enlarge .

Navy Map of Christmas Island, to the left - compare with the land surface on the card to the right a click to enlarge .

Its climate is special : the island is located in the equatorial dry zone, only watered by the rains during El Niño years. Precipitation is not fully withheld due to the nature of its soil, and the lack of vegetation.

The arid climate has an impact on the flora and fauna ... natural vegetation consists mainly of low shrubs and meadows, supplemented by a few coconut palms and Pisonia in various places.

The avifauna consists mostly of seabirds, and the only land bird native, endemic, is the Bokikokiko / Acrocephalis aequinoctialis. Some of Rimitara Lorikeets (or Kuhl's Lorikeet) were reintroduced, with little success, given the sub-optimal habitat.

Access to Cook Island and Upua and Tabu motus are subject to authorization
, and considered as protected area.

Kuhl's Lorikeet - photo Mark Van Beirs / Birdquest

Kuhl's Lorikeet - photo Mark Van Beirs / Birdquest

The nuclear testing:

During the Cold War, Christmas Island was the site of numerous nuclear tests carried out at the time without any consideration for local people. They were usually not evacuated ... and data on the human and environmental impact of these tests remain challenged !

A battery of tests was first conducted by the United Kingdom, which exploded its first hydrogen bomb over the southeastern tip of Christmas Nov. 8, 1957, followed the series of tests Grapple Y & Z.

The United States took over in 1962, with Operations Dominic I and II, consisting of many successful nuclear tests. In 1969, the military interest in this kind of site ceased, and the facilities were converted for civilian use.

Details of the
opérations Grapple and Dominic I & II are available by following the links.

The first British H-bomb test passed the 11/08/1957 / test Grapple X Round C1, above the southeastern tip of Christmas Island - photo RAF

The first British H-bomb test passed the 11/08/1957 / test Grapple X Round C1, above the southeastern tip of Christmas Island - photo RAF

Hastings TG 582 bomber flies over Christmas in August 1956 - photo taken by his navigator Denis Hobbs.

Hastings TG 582 bomber flies over Christmas in August 1956 - photo taken by his navigator Denis Hobbs.

Sources :

- Pacific Islands Benthic Habitat Mapping Center – Pacific Remote Island area / PRIA - link

- Geology and geochronology of the line islands - Schlanger - 2012 - Journal of Geophysical Research  Solid Earth (1978–2012)

- Center for coastal and ocean mapping / Joint Hydrographic center – Line islands

- Pacific Remote Island Area (PRIA) - link

- Wikipedia – Kiritibati island – Operation Grapple – Operations Dominic I & II

Lire la suite

<< < 1 2 3 4 5 6 7 8 9 10 > >>

Articles récents

Hébergé par Overblog