Articles

Ancient Hills

These peaks slipping above the clouds are the Nandi Hills, found about 40 kilometers west of the city of Bengaluru (Bangalore) in southern India. The view here is snapped on a cloudy day from the Western Ghat Mountains that run down India’s western coastline.

These small knobs are geologically fascinating. If you just go to Google Earth and look at a satellite photo of the area (linked below) you can make out an odd lineament running north-south across the continent for almost 400 kilometers.

This long feature is known to geologists as the Closepet granite. This granite is more than ½ of the age of the Earth; it formed just over 2.5 billion years ago at the end of the Archean.

The rocks are granitic in composition but have been metamorphosed like many rocks of this age; commonly pieces of this granite contain foliations and other marks produced during metamorphism but geologists still call it granite. The term granite indicates the composition of the rock whereas the term “gneiss” doesn’t necessarily tell you what the rock is made of; hence the name the “Closepet Granite” even if it has been metamorphosed to a gneissic texture.

Most granites I’m familiar with (see these for a great example: http://tmblr.co/Zyv2Js1aWDLq5) tend to form plutons: roughly spherical shaped magma chambers that show up on the Earth’s surface as circles, sometimes inter-linked to form mountain ranges like the Sierra Nevada Batholith. However, this granite does not.

This elongate structure owes its shape to gigantic plate tectonic forces at the time. This granite crystallized deep in the crust beneath a massive shear zone. In other words, there was a gigantic strike-slip fault on top of this granite. As this granitic magma chamber was building, the rocks above it were shearing and slipping, dragging the granite along with it and leaving a deposit hundreds of kilometers long and only 30 or so kilometers wide.

-JBB

Image credit: Koshy Koshy
https://flic.kr/p/5s76Sw

More:
Google Earth: http://bit.ly/1NEKAM6
https://www.sciencedirect.com/science/article/abs/pii/S0191814102000469http://bit.ly/1EnBXCz

Watch how the clouds sometimes punch through to a higher layer in the atmosphere - that’s the part where it becomes a “pyrocumulus”, the cloud is going so high under its own energy that it begins condensing water and forming a normal water cloud.

evosia 

Timelapse of the#pyrocumulus cloud from the #lakefire north of Los Angeles

20 mile round-trip hike to Reflection Canyon, in Glen Canyon National Recreation Area, Utah.

ammonitefan16

A nice dac  ammonite I collected on my last visit to kettleness, it split very well showing a lot of nice detail on the inside of the nodule

emeraldcityminerals:

Mississippian age Crinoid - Cactocrinus Imperator.  From Gilmore City Formation, Iowa

Visiting the areas around Reykjavik including Gulfoss, Seljalandsfoss, and the geothermal areas.

je_fossils

The Belemnite Marl at Seatown this morning

Savage 10 metre fish of the Silurian and Devonian

Heavily armoured piscine torpedoes with fierce teeth roamed the oceans in the early days of fishes, in fact the Devonian era is called the age of fishes by palaeontologists as they had a huge burst of speciation and diversified to fill most marine ecological niches during this time. The now extinct (fortunately) class known as placodermi (plate skin in Greek) was the apex predator of these long gone waters, and thrived from 438 to 358 million years ago, dying out at the end Devonian mass extinction (one of the lesser ones).

They were amongst the first fish with proper articulated jaws, and evolved the structure that passed on to modern fishes. They also developed pelvic fins, which eventually changed into legs as the first tetrapod fish came onto land in the late Devonian, and the first live birth was discovered in a fossil from Western Australia (which pushed back the history of live births by 200 million years). Many were bottom dwelling predators in both fresh and salt water in the shallow seas, though some herbivorous species existed alongside them.

We illustrate the post with a herbivorous genus called Bothriolepis around a metre long, and the head of a large species of Dunkleosteus, from the late Devonian. Only the armoured front end of these fishes often survives the vagaries of fossilisation.

Loz

Image credit: 1 Dunkleosteus sannoble: Mitternacht90
2 Bothriolepis: Haplochromis

Sand Sea

This amazing image comes from Namibia’s amazing Namid-Naukluft National Park. In the far distance of this shot, you see the Atlantic Ocean at the edge of these sand dunes. These dunes are found at the edge of the Tsauchab river, which is one of several rivers that flow from the central part of South Africa into the Namib desert. The Tsauchab does not reach the ocean, all the water is lost into the ground and as evaporation before it could do so, but all of the sand and sediment carried by that river is left behind. Over time, the winds of this desert have sculpted that sand into these high dunes.

Sand dune shapes are determined by wind directions and sand supply. One dominant wind direction can create linear or barchan (crescent) dune shapes, while this more complicated shape is called a star dune. These are produced here by the combination of winds coming from the southeast along the coast, winds coming down the river valley, and winds from the northwest during the winter.

This desert is in part shaped by its proximity to the Atlantic Ocean. Here, cold water from Antarctica is brought north, limiting evaporation and leaving the land dry despite the ocean being right here.

-JBB

Image credit: David Lynch via epod
https://epod.usra.edu/blog/2011/07/namib-desert-dunes.html

Reference:
https://earthobservatory.nasa.gov/images/42396/tsauchab-river-and-sossus-vlei-lakebed-namibia

nateinthewild

Ok so this week’s #timelapsetuesday is coming on Wednesday because I spent all night Tuesday out creating timelapses! Then, I woke up this morning to an inversion layer (literally my *absolute* favorite photography conditions) and everything from last night is now forgotten. Anyhow, please enjoy.

Canadian Dike

This single layer of rock standing above the surroundings is an ancient piece of igneous rock. It is a dike, a vertical path taken by molten rock as it moved upwards through the crust. The igneous rock formed a crystalline structure that was difficult for the environment to erode, letting it stand up as seen here.

Canada is a piece of a craton, an ancient assembly of continental fragments at the heart of a continent. The core of Canada contains rocks that are several billion years old and since it first assembled it has been subject to repeated igneous events. In fact, there have been so many different magmatic events that I can’t tell which one this dike represents. It could be a remnant of the Griffin intrusions, which happened over 2 billion years ago and marked a breakup event between several Canadian provinces, or it could have been formed during the younger Mackenzie Dike Swarm that cuts across much of the heart of Canada.

-JBB

Image credit:
https://commons.wikimedia.org/wiki/File:Nunavut_dyke.jpg

Reference:
http://www.largeigneousprovinces.org/gallery

rainie-is-seasonchange:

Little Brewster Island, Boston, Massachusetts.

Original caption:

“Two weeks well-spent in Gibraltar amidst the pandemic. This time around we got to explore underwater. Took the PADI open water diver course and did a LOT of diving! Very cool experience with the marine life, wrecks and especially all the people we got to meet and dive with. Such a nice community eager to help out, share some tips and stories.
A very BIG thanks to Dive Charters especially to our awesome instructors Gui and Vinny! We had a great time and learned a lot diving with these guys.”

heysoap

Lever de lune en Dordogne

Snaking through the sky

This panoramic photograph of the Milky Way was taken in Serpentine National Park. The falls are formed where water tumbles over the Darling Scarp, a major fault near the coast in Western Australia that separates ancient, Precambrian aged crust from younger rocks in the Perth Basin to the west.

This park is only a half hour of travel from Perth, an urban area with over 2 million people, yet this location is free enough from light pollution to create this shot.

-JBB

Image credit:
https://flic.kr/p/xQH9ZR

Ref: https://www.dpaw.wa.gov.au/images/documents/parks/management-plans/decarchive/serpentine.pdf

tirsostudios

Feliz noche desde Mirador del Fuego, Acatenango, El volcán de fuego demostrando el esplendor de nuestro país

Fuego volcano, behind Acatenango, erupting at night.

Pulpit terrace print

This is a really neat image. This is Pulpit Terrace, part of Yellowstone’s Mammoth Hot Springs named because it looks so much like a preacher’s pulpit from the side that you can find old photographs of people standing behind it and looking like they’re preaching (see our twitter page below). This image shows it as it appeared in 1898, but it’s not a photograph.

This is a photomechanical print, a printing of an area based on a photographic negative. The color in the shot may reflect a bit of artistic expression, but this is still a pretty neat, color look at how a terrace in Yellowstone could have appeared before the advent of color photography, and what the rocks of Mammoth Hot Springs looked like before large numbers of visitors affected the landscape.

-JBB

Image credit: Photochrom Co/Library of Congress
http://www.loc.gov/item/2008678251/

More:
https://twitter.com/TheEarthStory/status/639507092487958528

Walkthrough (Socially distant/masked) of Denver Gem and Mineral Show displays