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Photographer: Sue Strickland

Summary Author: Sue Strickland

Slicing through the center of Iceland is the Mid-Atlantic Ridge. This is the boundary between the North American and Eurasian tectonic plates. Tectonic plates are the enormous slabs that make up the earth's crust. The North American and Eurasian plates are slowly separating, at a rate of about three millimeters each year. There are many places on the Earth where two tectonic [not continential] plates are drifting apart, but most of these sites are deep under water. Thingvellir National Park, in southwestern Iceland, is one of the few spots in the world where an underwater ridge rises above the water surface. This enormous geologic rift has created spectacular scenery, including dramatic cliffs and Iceland's largest natural lake.

Over the past 10,000 years the Thingvellir Rift Valley has been changed in appearance by the spreading and sinking of the Earth’s crust and by earthquakes. Measurements suggest that the floor of the valley has widened 230 feet (70 m) and sunk by 131 feet (40 m) in the space of 10,000 years. Not only is the mid-ocean ridge changing the geography of Iceland, it’s also responsible for the volcanic activity which created the island. As the two tectonic plates shift, fissures periodically form in the crust. Over time, these gaps allow molten rock from underground to surface as lava, creating Iceland's many volcanoes. Iceland is one of the most geologically active places on Earth with more than 15 volcanoes that have erupted in the last century.

The top photo shows visitors walking along the edge of the North American plate. The bottom photo was taken from the North American plate, looking across the Thingvellir Rift Valley to the Eurasian plate on the other side. It shows how much the two plates have separated over the last 10,000 years.

Photo details: Camera Maker: Canon; Camera Model: Canon EOS DIGITAL REBEL XTi; Focal Length: 18mm; Aperture: f/16.0; Exposure Time - TOP: 0.0080 s (1/125); Exposure Time - BOTTOM: 0.0063 s (1/160); ISO equiv: 400; Exposure Bias: -0.33 EV;Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Manual; Flash Fired: No; Color Space: sRGB