The 6-million-year-long prehistoric eruption that built a giant’s road
In 2017, my grandma took me, my cousin, and my two aunts on a cruise around the British Isles. WOW Air still existed at this point, so my cousin and I decided that on our way there, we would spend about five days in Iceland. Personally, I enjoy exploring nature much more than cities, so I was really excited. Because we were there for such a short period of time, we took two organized day-trips departing from Reykjavik, in order to see as many sites as possible.
On our second tour day in Iceland, we went to the Reynisfjara beach near Vík, Iceland's southernmost village. The beach is gorgeous, with crashing waves, black sand on the shore, jagged sea stacks in the water that made me imagine nesting dragons, and huge walls of stone columns facing the water.
Reynisfjara Beach, Iceland.
(Bailey Cohen-Krichevsky)
These columns are incredible. They’re vaguely hexagonal, and about 3 feet wide. Some of them were 2 feet tall or less, while others soared 60 feet into the sky. In places, they almost formed natural staircases, which let you clamber up them. The columns, with the black sand, the crashing water, and the cloudy sky made for a dramatic scene – we even saw a couple having a very fancy photoshoot on them!
Basalt columns at Renisfjara Beach, Iceland.
(Bailey Cohen-Krichevsky)
Fast-forward a week or so, when we got off the cruise ship in Belfast. We drove an hour to see the Giant's Causeway, and I had a bit of a sense of déjà vu. You see, the Giant's Causeway is another set of basalt columns. They're actually from the same prehistoric flood basalt. These ones are just a lot more horizontal. So instead of a wall of columns, they look kind of like a road - hence, Giant's Causeway. They’re so regular that it's almost hard to believe that they're not man-made, so I can definitely see where the idea of a road made by a giant came from.
Giant’s Causeway, Northern Ireland.
(“Giant’s Causeway (14) by Chmee2, CC BY 3.0)
So, what is basalt, and why does it form these regular columns?
The type of rock that forms both the soaring columns in Reynisfjara and the stony boulevard in Northern Ireland is basalt. Basalt is a dark-coloured rock that is created when lava cools and hardens. Rocks like basalt that are made of cooled lava are called igneous rocks. There are different theories about why basalt can cool into columns like these. The most widely accepted theory has to do with the way that the lava contracts as it cools. Cracks start forming at a right angle to the direction that the lava flowed, and these spread out to make a network of cracks – think about how mud dries. The size of the columns depends on how fast the lava cools: faster-cooling lava makes thin columns, and slower-cooling lava makes wider columns
The cracks spread in cooling lava a bit like in this dried mud.
Continents on the move
If these rock formations were made in the same eruption, why does it take an airplane to get between them now? Well, our continents weren’t always in their current spots. They actually move around very slowly: North America and Eurasia, for example, are moving apart at about 1 inch per year. Continents can come together, and they can also break apart. 335 million years ago, all of our current continents were mashed together in one supercontinent called Pangea. When Pangea broke apart, it didn’t break apart all at once: it separated in stages. During one of the last stages of Pangea’s breakup, a volcanic eruption that lasted for as long as 6 million years broke open the North Atlantic Ocean. This eruption created igneous rock formations as far apart as Greenland, Iceland, Scotland, and the Faroe Islands. Some of these rock formations include the basalt columns I saw in Iceland and Northern Ireland! The huge volume of lava that pushed the continents apart over millions of years contracted as it cooled and created these columns.
In a series of coincidences upon coincidences, about a year after I took this trip, I took a few courses in earth science at the University of Toronto Mississauga. I learned about all kinds of cool things like these basalt columns, and was actually given the assignment that inspired me to get a degree in science communication. Inspiration can come from anywhere. Exploring the world around you is always worth it, and always, always keep learning.
Pangea’s breakup
(Public Domain)
In loving memory of my grandma, Miriam Cohen. May her memory be a blessing.
References:
Á Horni, Jim, John R. Hopper, Anett Blischke, Wolfram H. Geisler, Margaret Stewart, Kenneth McDermott, Maria Judge, Ögmundur Erlendsson, and Uni Árting. “Regional Distribution of Volcanism within the North Atlantic Igneous Province.” Geological Society, London, Special Publications 447, no. 1 (July 11, 2017): 105–25. https://doi.org/10.1144/sp447.18.
Ashwell, Paul. "ERS111: Lecture 4 Plate Tectonics." ERS111: Earth, Climate & Life. Class lecture at the University of Toronto Mississauga, Mississauga, ON, Fall 2018.
Ashwell, Paul. "ERS111: Lecture 5 Volcanoes and the Climate." ERS111: Earth, Climate & Life. Class lecture at the University of Toronto Mississauga, Mississauga, ON, Fall 2018.
Evers, Jeannie, ed. “Continental Drift.” National Geographic Society, October 9, 2012. https://www.nationalgeographic.org/encyclopedia/continental-drift/.
Hetényi, György, Benoît Taisne, Fanny Garel, Étienne Médard, Sonja Bosshard, and Hannes B. Mattsson. “Scales of Columnar Jointing in Igneous Rocks: Field Measurements and Controlling Factors.” Bulletin of Volcanology 74, no. 2 (2011): 457–82. https://doi.org/10.1007/s00445-011-0534-4.
Marshak, Stephen. Essentials of Geology. 5th ed. New York, NY: W.W. Norton, 2016.