Saddle

Our van rumbles down a road that leads to the very heart of the tectonic rift system while our guide, David Sigthorsson, tells us about the myths of Norsemen who settled his home country.Embraced by volcanoes on either margin, this foreign landscape intensifies all of our senses. Long stretches of evergreen grasslands, yellow and orange wetlands, and little streams of bright-blue water pass by my window as if on their way, as we are, to Thingvallavatn Lake, two hours east of Iceland’s capital, Reykjavik. Rain and glacial water traverse unconventional routes on their way into this basin. Most of the glacial water from Iceland’s second-biggest glacier, Lángjökull, filters through the porous basalts for hundreds of years before welling up in the many fissures found around the lake. That is why it is so clear and clean, a diver can drink from it. But there is a price to visiting this wondrous place: water temperatures of 36 degrees.A convenient staircase allows me to descend into Silfra, or “Silver Lady,” one of many ruptures caused by tectonic activity. The cleft is quite narrow, its deepest point around 195 feet. A steep wall of magmatic rock near the entrance guides me into a labyrinth of cavities, arches, troughs and saddles filled with the planet’s purest fresh water. Above my head, a shimmering effect turns the surface into a silvery mirror. Only at the very end of the dive am I reminded of the limiting temperatures.A short break in the bright but faint summer sun gives us enough warmth to continue our dive in a shallow lagoon. At the bottom, just above bright-white sediment, tiny gas bells cause wisps of light-green algae to flutter softly in their stream. Soon we re-enter the main fissure, and a cathedral of massive basaltic boulders steals my breath. Here Earth is split in two by energy coming from the deep mantle below. We are diving between continents, on the Mid-Atlantic Ridge system.Geologically speaking, Iceland is very young, roughly 20 million years old. Much of its landscape has not yet been leveled; Europe’s most powerful waterfalls tumble from great heights as they carve their way into lava fields. It is one of the most active places in Europe, home to more than 30,000 live volcanoes.The island consists of volcanic rock generated at the Mid-Atlantic Ridge, a mountain that stretches north to south along the entire Atlantic Ocean. Here two tectonic plates are being pushed apart, leaving a gap in the middle, where hot magma rises and crystallizes on the ocean floor; much of the ridge lies below the surface of the water. In some areas, the ridge rises above sea level, creating this island country. Iceland is also situated above a hot spot, a region of high volcanic activity due to the rise of a hot mantle plume, similar to the Hawaiian Islands. Mantle plumes come from much deeper than the average mid-oceanic ridge — nearly 2,000 miles below the Earth’s crust.