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5 June 2018
Cross-bedding in Archean komatiitic ash deposits
Cross-bedding isn’t just for modern sedimentary deposits; you can find it in truly ancient ash deposits too! Let’s head to South Africa and take a look.
12 January 2018
Friday folds: Hayden Butte (“A Mountain”), Tempe
In keeping with the Arizonarific theme of this week’s posts (thanks to my participation in the 2018 Structural Geology and Tectonics Forum), I thought I would wrap up my ‘geology of the Phoenix area‘ posts with a walk I took on my last day there. This was to what Google Maps calls “Hayden Butte,” but the locals call “A Mountain.” Not “a mountain,” but “the mountain called ‘A‘.” It has …
1 December 2017
People and Pyroclastics: Mount Agung at the Confluence of Science and Society
A guest post from an American expat living in east Bali, displaced with his family from their home due to Mount Agung’s recent eruption, and trying to help out as best he can.
22 September 2017
Friday fold: bend in a vesicular lava flow, Etna
It’s the First Friday of Fall! Here’s a sort of fold to help you celebrate: a section through a ∧ shaped bend in a vesicular basalt flow from the eastern flanks of Mount Etna in Sicily. It’s due to volcanic lava flowing rather than ductile deformation of a pre-existing solid rock (our usual habit with this feature), but I think we can appreciate it regardless:
15 July 2017
Flow-banded rhyolite from Vulcano, Italy
I collected only a single rock on my summer travels in France and Italy. (Those of you who know me will realize how extraordinary this low number is!) It’s a flow-banded rhyolite from Vulcano, in the Aeolian Islands north of Sicily a few weeks ago. It contains porphyritic vesicular basalt xenoliths. I featured a similar sample on Twitter yesterday on the occasion (supposedly) of “International Rock Day”: For #InternationalRockDay , …
1 May 2017
Accretionary lapilli from Archean volcanic eruptions
Volcanic “hailstones” called accretionary lapilli rained down on South Africa 3 billion years ago, and have survived to be seen in the present day, along the R40 road through Barberton Mountain Land, near the Bulembu border crossing into Swaziland.
26 April 2017
Pseudocraters at Lake Mývatn, Iceland
Near the southern end of Lake Mývatn, astride the Mid-Atlantic Rift in northern Iceland, lies a field of “pseudocraters” that result from steam explosions beneath a fresh lava flow. Put on your head-net and join us to check it out!
2 March 2017
A virtual field trip to the Grind of the Navir
On the northwestern coast of the Northmavine Peninsula of Shetland, there is an unusual coastal landform: a gate-like entrance to an elevated amphitheater, like something out of Tolkien, and a storm beach of slab-like boulders inland of that.
1 February 2017
An oddball at Eshaness
In eastern Shetland, the sea chews away at the innards of a Devonian stratovolcano. But there’s an odd visitor there too – and we’re not talking about the blogger.
11 January 2017
More Messengers from the Mantle
Since I showed off the 3D kimberlite intrusion breccias yesterday, I feel as if I owe you some other photos from that lovely exhibit at the IGC. I apologize for the poor quality of these photos – the gorgeous samples were behind glass and brightly lit, which made photography difficult. But the rocks are sooooooooo pretty, I think you’ll enjoy viewing them just the same. Let’s start with a gargantuan …
Callan Bentley is an assistant professor of geology at Northern Virginia Community College. He is a fellow of the Geological Society of America and the President of the Geo2YC division of the National Association of Geoscience Teachers. Callan is a contributing editor at EARTH magazine and Past President of the Geological Society of Washington. He lives in the Fort Valley of Virginia.
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