#phonolite

[rh35211]

Wyoming is the least populated state in the U.S.

Despite being the least populated, Wyoming is the 10th largest state by area. This leads to a very low population density

[earthstory]

Roque de Agando

The island of La Gomera is covered in striking volcanic rock formations. La Gomera is one of the seven main islands of Spain’s Canary Islands. They are located in the Atlantic Ocean and were formed by the Canary hotspot, a mantle plume underlying the archipelago.

In the center of La Gomera, three impressive mountains called Los Roques rise above their surroundings. They are located within the Garajonay National Park which is a popular tourist destination. The Roque de Agando is the highest of these mountains and has a south face rising 220m above the ground. It was once a popular climbing spot, but since then the Roques became national monuments and climbing is now forbidden.

The Roques are so-called volcanic plugs. Volcanic plugs are a mass of solidified magma filling a volcanic pipe. The Roques are made of phonolite, a relatively uncommon volcanic rock type often associated with hotspot volcanism. Phonolite is a very hard type of rock and very resistant to erosion in comparison to the surrounding softer rocks. This effect has left these impressive mountains rising tall above the island.

Xandi

Image Credit: https://bit.ly/2EaHKze Source: https://bit.ly/2S0P7gn

[earthstory]

Hoggar Mountains, Algeria

This image shows an ancient volcano located in southern Algeria. After some searching, I believe the correct name for this object is the Lharen phonolitic plug.

This photo was taken in an area of southern Algeria known as the Hoggar Mountains which makes up the Ahaggar National Park (Hoggar and Ahaggar seem to be interchangeable in the translations).

The Hoggar Mountains sit in the heart of the Saharan desert close to the southern tip of Algeria, close to the Tropic of Cancer. They sit on top of a broad plateau and are composed of volcanic rocks erupted over the last 40 million years. The most active portion of the volcanism took place between 12 and 20 million years ago and the rocks in this image date from that period.

This outcrop is a volcanic plug, the remnants of the inside of a volcano. This rock was formed by lava that migrated upwards inside a volcanic system but was stranded when the supply from below was cut off and the volcano died.

The rocks show columnar jointing; that’s the pattern of near vertical lines and cracks you see. Columnar jointing always forms lines in the direction cooling is happening; this rock cooled from above, suggesting that it was originally surrounded by a larger volcanic mass that shielded the sides from cooling.

Most of the outer volcano has been eroded away, but the plug in the volcano likely cooled slowly, generating a crystalline rock which is strong and resistant to erosion. The debris pile around it is some remnants of the erosion of the plug and the mountain around it. The rock itself is a phonolite, a common type of magma found in crustal igneous settings.

The cause of the volcanism in this area is enigmatic. The volcanic rocks are coming through the thick crust of northern Africa but have chemical signatures suggesting they were derived from the mantle. They could have been formed due to a small hotspot underneath this portion of Africa, or they could represent a product of the collision between Europe and Asia far to the north, which could break the crust throughout the continent and cause enough movement within the mantle to cause generation of the magmas that eventually formed this plug.

-JBB

Image credit: Patrick Gruban http://www.flickr.com/photos/gruban/137349085/

A data compilation source thanks to Dr. Anderson’s page: http://www.mantleplumes.org/Hoggar.html

World Geography entry: http://world-geography.org/mountain/12-ahaggar-mountains.html

http://www.volcanolive.com/tahalra.html

[anywhereinafrica]

Once upon a time in Africa, the colonizers got beaten up and their survivors limped back home The Adwa Mountains

[geoworldtravel]

Wonderful day on La Gomera today. We did a complete loop of the island seeing the inner eroded plumbing of a Miocene and Pliocene volcano. We saw many #phonolite and #trachyte intrusions + #dykes as well visiting #garonjonay national park and #worldheritagesite In the park we walked and checked out the unique botany. Finally we boarded a ferry to La Palma which will be our base for the next 4 nights. #lagomera #canaryislands #geology #geotourism (at La Gomera, Islas Canarias) https://www.instagram.com/p/BrVoJBsg6Nz/?utm_source=ig_tumblr_share&igshid=1haochde2ab47

[anywhereinafrica]

Mount Suswa Inner Caldeira

[earthstory]

Sunrise at Devil’s Tower This photograph catches the iconic volcanic feature in Wyoming peering out through the trees just after sunrise. Devil’s tower is the remnants of magmatism about 50 million years ago. It is made of a fairly rare type of magma known as a phonolite; a type occasionally found when magmas move up through thick continental crust. It’s clear that Devil’s Tower is a volcanic feature; the rocks are igneous and the fracture pattern is produced when igneous rocks cool and shrink due to thermal contraction, but many other details of this feature aren’t understood due to erosion.  It’s unknown, for example, if the magma that produced Devil’s Tower ever erupted at the surface; any remnant of a surface volcano eroded away long ago. Today, only the deepest part of the volcano’s throat appears at the surface. -JBB Image credit: © Daniel McVey with permission.  See more of his work here: http://www.danielmcvey.com/ https://www.facebook.com/PhotographybyDanielMcVey/

[earthstory]

The image below is of Devils Tower, in Wyoming, USA. It is a recognised National Monument. The Rock Type that makes up Devils Towers is known as a Phonolite, a rare form of extrusive igneous rock, of medium composition. A phonolite has a high silica content, and there are only 2 known ways of producing a rock of this composition. Hot Spot volcanism, and Continental Collision. The type found at Devils Tower is coarse grained, and includes large crystals of the mineral Feldspar. The origin of the "Tower" is hotly debated among geoscientists, but they all at least agree that it was the injection of igneous material into the host rock (which is a series of Jurassic sediments) as opposed to a volcano; although earlier theories included a volcanic plug. Although most geoscientists agree on what it is, none can come up with a suitable explanation as to how it was intruded, however it may have been related to the uplift of the Rocky Mountains and Black Hills, around 65Ma. It is unknown whether or not the igneous material ever reached the surface; age estimates the intrusion at around 45 million years ago with erosion probably uncovering it about 2 million years ago. The characteristic columnar shape of the igneous material formed from compressional cooling, in the same way the the Giants Causeway in Ireland way formed. As erosion continues in the area surrounding the Tower more and more of it will be exposed, and scree and debris at the base of Devils Tower indicate it was once much wider than what we see today. -LL For more information head to the following links: http://www.scienceviews.com/parks/devilstowergeology.html http://www.nature.nps.gov/geology/parks/deto/index.cfm