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Geological understanding of the world’s continents and oceans was only just beginning to emerge when New Zealander Edmund Hillary with Nepali Tenzing Norgay scaled the six-mile-high Mount Everest in 1953 and US Navy lieutenant Don Walsh with Swiss engineer Jacques Piccard plunged to the one-mile deeper ocean floor east of the Philippines in 1960.
The English philosopher Francis Bacon (1561-1626) noticed the jigsaw fit of Africa and South America, suggesting that these were formerly parts of one supercontinent. But why and how land masses ‘drift’ apart, only to then collide and push up mountains tens and sometimes hundreds of millions of years later, were questions that would await 20th century remote sensing technology of the ocean floor. This developed first in the North Atlantic because of its world’s busiest shipping and submarine routes. And Iceland would emerge as a spectacularly unique laboratory.
A remote island the size of Wales at the Arctic Circle, Iceland has about 350,000 inhabitants and an annual tourist volume nearing 700,000. Its recent volcanic eruption, 15 miles from the capital Reykjavik, fascinated the world, attracting hordes of reporters and onlookers to a two-hour hike for viewing of its fiery action. Causing a massive travel problem, though, was the 2010 eruption of Iceland’s Eyjafjallajökull volcano under an icecap. With its ash rising to the jet stream, airspace above and downwind was closed to air traffic for at least a week.
I have been fortunate to visit Iceland three times. First to its most popular southwestern corner and the northern area around Akureyri during an educational family cruise from the British Isles and Norway via the Shetland Islands and Faroe Islands, then as co-host of 820-mile Ring Road adventures with an Icelandic geoscientist and meteorologist for members from the North Carolina Museum of Natural Sciences. I was however mindful of an earlier riveting experience. The 1960s were an exciting period to embark on a degree in geology but aerial footage of an actual geological event in the classroom was a rare treat. A film documenting a new volcanic island during the mid-1960s, called Surtsey, 20 miles from the south coast of Iceland was unforgettable. Formed quickly by undersea eruptions that built a mile-wide island almost 600 feet high, but soon inactive with erosion of its cliffs by storm waves, it has been protected as a pristine natural laboratory to study the course of colonization by fungi, plants, birds, and invertebrates.
Below the fishing grounds of the Earth’s continental shelves, typically out to a depth of a hundred fathoms, are basins four or so miles deep that flank mid-ocean mountain ranges dislocated by transverse faults. Eroded remnants of unseen former volcanoes, called seamounts, dot the ocean floors. The Mid-Atlantic Ridge is part of a 40,000-mile-long mountain range that encircles the globe, almost all of it hidden from view. It delineates a crustal mosaic of interlocking plates that are either converging, diverging, or sliding laterally from each other. Iceland is the only place to observe the Mid-Atlantic Ridge with its divergent volcanic and related earthquake dynamics of seafloor spreading. North America is the west half of the North Atlantic tectonic plate that begins in Iceland and extends to the Pacific coast mountains of Canada and the United States.
Taking a hemispherical view, the western and eastern sides of Iceland are respectively the trailing edges of the North American and Eurasian Plates that are sliding in opposite directions, thereby widening the Atlantic Ocean. While only at the average rate of an inch or two per year, this can nonetheless open a 100-million-old ocean basin that takes half a dozen or so hours to fly across. Today’s Atlantic Ocean began to open after a preceding ocean, called Iapetus, had narrowed to push up accumulated sediments into mountains of which the Appalachians are a survivor. The hot spot sources for Iceland’s volcanism are under vertical cracks, called fissures, and cones along the Mid-Atlantic Ridge. As molten rock is pushed up to become lava and solidifies, the crust is incrementally pushed apart: as this happens, zones of older and older rocks are increasingly separated. The eastern and western extremities of the Iceland reach ages of a dozen or so million years whereas the ocean floors to the east and west of Iceland, adjacent to Greenland and Norway, are as old as 50 million years.
In mid-oceanic volcanic terranes such as Iceland, iron-and-magnesium rich, low viscosity lava results in relatively long flows over gentle slopes. Crusts form in an hour or so but for several months these can insulate red-hot lava which may still be flowing. The road from Keflavik Airport to Reykjavik is flanked by an overlapping series of lava flows from a few hundred to tens of thousands of years ago. Ranging from unvegetated to lichen-and-moss covered, the black basalt left a landscape that is hummocky, often cracked, and sometimes left cratered from gas-bubble explosions. These flows separate the dramatic sites of recent volcanic eruptions along the central Mid-Atlantic Ridge across Iceland. Its largest volcano, almost 5,000 feet high, is Katla which has erupted almost two dozen times during the last thousand years, but not significantly over the last century.
Unlike zones where tectonic plates converge, regions like Iceland typically have frequent, but relatively low magnitude, earthquakes. Iceland’s typically one hundred or so daily tremors are caused by volcanic activity and related seafloor spreading but are seldom felt. Since 1900 there have however been 11 earthquakes with a magnitude of 6 or higher but more than 1,300 with a magnitude between 4 and 5. I subscribe to a daily report of Iceland’s earthquakes: low magnitude 3 tremors are usual.
An extraordinarily positive outcome of Iceland’s volcanism is extensive tapping of its geothermal energy. The United Nations Environment Programme reports: “At the beginning of the 20th century, Iceland was one of Europe's poorest countries, its people relying on a precarious and polluting mix of imported coal and local peat for electricity. But over the next century, the island nation would pull off one of the great energy makeovers in history, casting off fossil fuels and embracing geothermal power. Today, nearly 100 percent of Iceland's electricity comes from renewable sources…”. In addition to the hard-to-miss energy installations and piping connections across the landscape, tourist awareness of geothermal energy comes from the splendor of hot springs and geysers where the ground either continuously or intermittently emits boiling water.
Yet another dramatic natural phenomenon in Iceland, covering about 10% of its area, are icecaps and glaciers. Most lie within Vatnajokull National Park, the largest icecap in Europe at almost 3,000 square miles. Like the world’s other ice-covered areas, it is decreasing due to global warming. Combined with rainfall that annually averages between 40 and 150 inches across the island, accelerated icecap and glacier melting leads to abundant waterfalls. The most dramatic ones occur along gorges eroded in stages by catastrophic floods from sudden release of ponded meltwater under, or at the margins of, icesheets and glaciers. The Icelandic term jökulhlaup, meaning a glacier outburst flood, has become adopted globally for historic and prehistoric floods of mammoth scale, such as the Channeled Scablands in the State of Washington. Iceland’s most severe floods result from volcanic heating below ice. The Earth Watching Project, which uses satellite imagery, described the jökulhlaup of November 1996 as flooding a coastal area up to 20 miles wide with icebergs up to 1,000 tons. The water level in the volcano’s six-mile-wide caldera under the ice sheet dropped suddenly by as much as 500 feet. An almost instantaneous discharge from a much larger jökulhlaup in the same area in 1755 has been estimated to have been 7.1–14.1 million cubic feet per second, apparently, and incredibly, comparable to the combined average discharge of several of the world’s largest rivers.
Bermuda is situated in the Gulf Stream east of the Carolinas. Known for its warmth and coral reefs, the most northerly in the Atlantic Ocean, it is almost 3,000 miles south of Iceland and coincidentally with almost the same annual tourist volume. But why do I put these two utterly contrasting vacation spots, with a 30°F difference in their sea temperatures, side by side? In 1972 a 2,600-foot drill core was obtained from beneath Bermuda: stacked rock of volcanic origin underlies ancient coral accumulations and today’s reefs. The island that would become Bermuda began 30-40 million years ago, much like the earlier-mentioned Surtsey off the coast of Iceland. Since that fiery beginning, the ocean crust around Bermuda, now a reef-capped seamount, has moved farther and farther away from the Mid-Atlantic Ridge. So although Iceland and Bermuda have the utterly contrasting landscapes of glaciers and coral reefs, such is the amazing process of seafloor spreading that they share the same origin!