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If you take a look at a map of Scotland, you'll notice an eerily straight line running through the highlands, this is the Great Glen Fault the product of half a billion years of time and geology.

Hosted by: Stefan Chin

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Sources:

https://earthquake.usgs.gov/learn/glossary/?term=strike-slip
https://www.geolsoc.org.uk/Plate-Tectonics/Chap4-Plate-Tectonics-of-the-UK/Caledonian-Orogeney
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998TC900033
https://www.geo.fu-berlin.de/en/geol/fachrichtungen/geologie/mitarbeiter_neu/Professoren/elinelebreton/LeBreton-etal_13_GGF.pdf
https://www.researchgate.net/publication/258616891_Cenozoic_reactivation_of_the_Great_Glen_Fault_Scotland_additional_evidence_and_possible_causes
https://www.tandfonline.com/doi/full/10.1080/17445647.2013.866369
https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/1998TC900033
https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3585.html
https://www.usgs.gov/science-support/osqi/youth-education-science/cenozoic
https://www.gsi.ie/en-ie/geoscience-topics/geology/Pages/Geology-of-Ireland.aspx
https://www.rte.ie/brainstorm/2018/0315/947589-ireland-on-ice-how-the-ice-age-influenced-our-placenames/
https://www.geolsoc.org.uk/Policy-and-Media/Outreach/Plate-Tectonic-Stories/Great-Glen-Fault
https://courses.lumenlearning.com/suny-earthscience/chapter/tectonic-stress-and-geologic-structures-2/
https://www.nationalgeographic.com/science/article/plate-tectonics

Images:
https://en.wikipedia.org/wiki/Great_Glen#/media/File:Great_Glen_Project_Station_M_-_geograph.org.uk_-_818230.jpg
https://commons.wikimedia.org/wiki/File:Great_Glen_Fault_map.png
https://commons.wikimedia.org/wiki/File:Scotland_from_satellite.jpg
[♪ INTRO].

If you look at a map of Scotland, you’ll notice an almost perfectly straight line through the Highlands that cuts from coast to coast. This region is home to plenty of valleys and peaks, but this valley is eerily straight.

Some interesting geology had to happen there at some point. And it wasn’t just one event. About 520 million years ago, most of the Earth’s landmass was split between two big continents: Laurentia and Gondwana.

This meant the modern-day island of Great Britain was separated, with the north of. Scotland sitting on Laurentia, and the southern half of the island on Gondwana. Then, the two landmasses collided around 430 million years ago during a period known as the Caledonian Orogeny, which joined the two pieces through the collision forming the island we now know as Great Britain.

This process resulted in the crumple and buckle of the Earth’s crust which also formed new mountains and fault lines all around the world. One of those new faults was the Great Glen, which is a strike-slip fault. This kind of fault happens when two tectonic plates shear, or move horizontally, past each other.

Other types of faults typically move one of the plates vertically, which creates mountains and all kinds of elevated terrain above the fault. But because of how these two plates collided with each other during its formation, the pieces of the Great Glen Fault move horizontally. And they’ve actually moved a few times since the formation of the fault.

The Great Glen Fault has occasionally reactivated and the two landmasses,. Laurentia and Gondwana, moved anywhere from 8 to 29 kilometers each time. This is a thing that faults do from time to time to dissipate built-up stress.

When force is applied by the two landmasses punching against each other, stress is created and when it reaches a tipping point, the plates shear and move in opposite directions, to relieve that built-up stress. The biggest reactivation happened relatively recently, sometime in the last 66 million years, possibly prompted by other parts of. Earth’s crust spreading apart nearby.

But why don’t we see straight lines like this more often? Well, these days, the Great Glen fault line is even more visible due to a string of lakes, or lochs. That’s because most of the islands of Great Britain and Ireland were covered in enormous ice sheets during a handful of Ice Ages over the last few hundred thousand years.

The glaciers around the Great Glen started receding over 10,000 years ago, carving a deep valley along the fault line that actually goes below sea level, making that straight line through Scotland even more visible. So, this straight fault line is the product of half a billion years of time and geology and it’s evidence of the large-scale events that formed Earth as we know it today! Thank you for watching this episode of SciShow!

At this point, we’ve made thousands of educational videos over the years, and we’ve been able to offer them for free because of our patrons on Patreon. So, to all of our patrons, thank you for what you do to make SciShow happen. If you’re not a patron but want to learn more about what that means, you can go to Patreon.com/SciShow. [♪ OUTRO].