The Silfra rift, and the Mid-Atlantic Ridge
This globe shows the ages of rocks that make up the seafloor of the Atlantic Ocean. The rocks that make up the crust on the ocean’s floor are youngest near the Mid-Atlantic Ridge. They are colored red in this picture.
The rocks are older (yellow, green) further from the spreading ridge. Molten lava pours out at the mid-ocean ridge. It hardens into basalt rock. Plate tectonics gradually moves the rocky seafloor away from the ridge. The oldest rocks in the Atlantic (blue) are about 180 million years old.
Image courtesy of NOAA.
How do we know what the ocean floor looks like?
Figure 6.8: A ship sends out sound waves to create a picture of the seafloor below it. The echo sounder pictured has many beams and as a result it creates a three dimensional map of the seafloor beneath the ship. Early echo sounders had only a single beam and created a line of depth measurements.
Located in the Þingvallavatn Lake in the Þingvellir National Park in Iceland,
The following text was written by Kaushik, Silfra: The Crack Between Two Continents, Amusing Planet:
Located in the Thingvallavatn Lake, in the Thingvellir National Park in Iceland, Silfra is part of the Atlantic rift – the dividing line between the continents of Europe and America.
It’s a huge crack in the earth’s surface, where the continental plates meet and which is slowing widening by about two centimeters per year.
In the deep waters of the Atlantic Ocean this crack is mainly unseen, but at Silfra, clear melt water of Icelandic glaciers make the rift visible.
The amazing visibility and accessibility makes Silfra a popular diving spot. Divers and snorkelers can float between the American and Eurasian tectonic plates and at places, can actually touch both continents at the same time.
The visibility is extraordinary at nearly 100 meters. The reasons for this outstanding clarity are two-fold. First, the water is cold – 2º and 4ºC – and remains at this temperature all year round. The coldness keeps the water free of aquatic life. Secondly, the water itself is of the purest form. It begins as distilled water when the leading edge of the glacier melts high up on the Hofsjokull mountain, 50 km away. This water then disappears and runs underground, to emerge once again in the Thingvellir national park. On its journey it is constantly filtered by porous lava rock, until is becomes so pure that it can be drunk without any form of treatment.
The Mid Atlantic Ridge is the longest mountain range in the world but for the most part, it is submerged deep beneath the surface of the Atlantic Ocean. The ridge includes a deep rift valley which runs along the axis of the ridge along nearly its entire length. This rift marks the actual boundary between the two tectonic plates – the Eurasian and the American.
Right between the tectonic plates lava underneath the earths crust flows out into the ice cold water of the Atlantic. The lava coagulates instantly, and over millions of years this process has formed the Atlantic Ridge.
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