Iceland’s Upper Crust
September 18, 2023
By Paul Erickson
COSMOS Explores the Mid-Atlantic Ridge
Thingvellir National Park, Iceland, provides a walkable pathway between the two tectonic plates.
At 4:30 AM on 18 November 1775, an earthquake rocked eastern Massachusetts, tilting church steeples, and sending the grasshopper weathervane atop Boston’s Faneuil Hall hopping to the plaza below. Today, geologists link this magnitude 6 quake with an undersea fault line—a fracture in the bedrock—27 miles east of Rockport.
As shocking as the 1775 Cape Ann Earthquake was, our local geology is relatively stable compared to the volcanic Mid-Ocean Ridge located roughly 1,500 miles east of Cape Ann.
Restless Planet
Circling the earth “like the seam on a baseball,” as oceanographers like to say, the 40,000-mile-long Mid-Ocean Ridge is a vast chain of volcanoes forming the longest mountain range on earth. Ninety percent of the ridge lies submerged in the deep sea.
A major segment of the Mid-Ocean Ridge is the Mid-Atlantic Ridge, where molten lava erupting out of colossal cracks in the earth’s crust spread apart major sections of the tectonic plates.
Along the ridge in the North Atlantic, the North American Plate has been separating from the Eurasian and the African Plates at a rate of about an inch per year. When the earth performs this Herculean task for about 165 million years, voilà, the result is the Atlantic Ocean. Even now, the Atlantic basin continues to widen as molten rock erupts and cools, paving new areas of sea floor.
World distribution of Mid-oceanic ridges. Iceland is located on the separation line of the Mid-Atlantic ridge tectonic plates.
Visit Thingvellir National Park
(Where you will not be vaporized by molten lava!)
As it turns out, you can visit the Mid-Atlantic Ridge! And if you prefer not to feel like a canned sardine in a compact, deep-sea submersible, sinking more than a mile below the waves to the ridge, just fly to Iceland and check out Thingvellir National Park, as I did last June. The park is one of the few places on earth where the Mid-Atlantic ridge rises above sea level. After a brief hike from a parking lot, you can stand smack dab between the colossal North American and Eurasian Plates.
Conveniently, this popular attraction on the Mid-Atlantic Ridge is not currently an active volcano, so tourists do not have to worry about molten basalt rock turning them into mostly water vapor.
And so, in this issue of COSMOS, we’d like to share some of our recent tourist photos of Iceland, including its portion of the Mid-Atlantic Ridge. Meanwhile, back in Rockport and Gloucester, you can rest easy, secure in the knowledge that your local earthquake zone is merely a placid, minor mid-tectonic-plate fault.
Still, on Cape Ann, it never hurts to watch out for falling weathervanes.
Paul and friends push apart the North American and Eurasian tectonic plates
DID YOU KNOW?
Ever since modern world maps were drawn up, even first-graders have remarked how North America and South America clearly fit together with Europe and Africa like pieces of a jigsaw puzzle.
Yet doubting scientists did not believe the kids, or more accurately, had not collected sufficient deep-sea data until the 1960s. That’s when the scientific community finally accepted the theory of continental drift—now called plate tectonics.
FACT CHECK
The estimated age of the Atlantic Ocean varies in scientific literature. The aforementioned “165 million years” appears in The History of the Atlantic, Scientific American, Vol 240, No. 6, June 1979.
