As soon as you arrive in Iceland, you can see that it is geologically unusual. Over much of its length, the bus ride from Keflavik airport on the Reykjanes peninsula to Reykjavik, the capital city, presents a scene as bleak as you can imagine. A dark, hummocky plain, Reykjanes peninsula was created by the same violence that both built Iceland and pulls it apart today.
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The dark lava plain of Reykjanes Peninsula is broken by linear rift faults, as seen in this view looking southeastward. In the distance steam rises from geothermal wells. |
Iceland sits astride the Mid-Atlantic Ridge, part of the world-circling undersea mountain system that is the locus of new crust formation. Iceland formed by the coincidence of the spreading boundary of the North American and European plates and a hotspot or mantle plume. As the plates moved apart, excessive eruptions of lava constructed volcanoes and filled rift valleys. Subsequent movement rifted these later lava fields, causing long, linear valleys bounded by parallel faults. These movements continue today, accompanied by earthquakes, reactivation of old volcanoes, and creation of new ones.
Some of the most active areas of new crust formation are in the southwestern parts of Iceland, accessible to all travellers. The trip from Keflavik airport to Reykjavik takes you along the edge of the North American plate where it meets the European plate. A drive to nearby Thingvellir valley, the site of the world's first parliament, reveals an older part of the rift system, where you can see both sides of the plate boundary in one sweeping panorama. A flight to the island of Heimaey gives you a glimpse of new land forming and of the hazards of living in the path of a propagating rift.
Reykjanes Peninsula is the onshore continuation of the Mid-Atlantic Ridge. The rift valley that lies at the crest of the ridge extends in a northeast direction along the peninsula, from Reykjanes, in the southwest, to Vogar and the airport road, in the northeast. Here the rift ends. Another rift starts about 10 km to the east and is parallel to the first. This one passes by Reykjavik on its eastern edge. This stepping pattern, called en echelon by geologists, repeats twice more. The fourth rift is quite long and eventually passes through Thingvellir to the northeast. The en echelon rifts are caused by the plate boundary, which runs along the peninsula, being not quite perpendicular to the spreading direction in this area. Energetically, it is easier for the crust to break in tension, rather than shear, so it does so whenever possible. With continued spreading, the offset ends of the rifts will eventually become connected by transform faults. A transform fault may be forming further to the east near Selfoss, where an east-west belt of earthquakes are causing some concern.
The rocks seen along the Keflavik-Reykjavik road are basalt lava flows, all younger than 700,000 years old. These rocks are somewhat similar to those found in Hawaii. Near the village of Vogar lie some of the youngest rocks in the area. Little or no soil or vegetation cover them. Geothermal wells have been drilled into the underlying hot rock and steam is extracted to heat the Icelanders' homes.
About 50 km northeast of Reykjavik is Thingvellir, a national park accessible by car or tour bus. The name means Parliament Plains and is the site of the old Icelandic legislative assembly, the Althing, first held in 930 AD. A natural amphitheater is created by the shear walls on the western side of the valley. At the base of the cliff is a small plateau, called Logberg or Lawhill, where laws were proclaimed, charges made and verdicts announced to the throng assembled in the valley below.
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Viewed northwards from the air, the cliff along the western side of Thingvellir rift rises above the valley floor. Logberg, the site of the Althing, the world's first parliament, lies near the center of the photograph overlooking the river flowing into Thingvellavatn to the south. |
A short way north along the cliff is Drekkingarhylur, or Drowning Pool, a crystal clear pool of water where unfaithful women were drowned and their male accomplices had their throat cut. This pool is part of Oxara, the river that flows from 300 m higher in the volcanoes to the north and eventually ends in Thingvallavatn, the largest lake in Iceland. Today the water flows over the cliff at Oxararfoss, a 10 m high falls. Originally the falls lay further to the north, but was diverted by the early Vikings to lie closer to the Logberg. Traces of the old river course can still be seen on the high plain above the valley.
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En echelon down-dropping faults form the eastern side of the Thingvellir rift on the edge of the European plate. This photo was taken from the air looking towards the northeast. |
Thingvellir is part of the extensional plate boundary that crosses Iceland. The extension appears as nearly parallel fissures and down-dropped fault blocks running along the length of the valley, best seen from the air (a small plane and pilot can be hired at the city airport). On the west (North American) side of the valley, the blocks step down toward the east, while the situation is reversed on the east (European) side. Thus the valley floor is a linear block that has subsided as the valley walls were pulled apart by plate motions. Geologists estimate that the valley walls are moving apart at a rate of about 3 mm per year, much less than the 21 mm per year rate measured on the Reykjanes peninsula. The floor is subsiding at a minimum of 0.4 mm per year, with a total subsidence of 70 m, indicating activity for at least 100,000 years. The fact that fissures at Thingvellir cut 9000 year old (geologically young) basaltic lava and that severe earthquake activity occurred as recently as 1789 shows that the action continues today.
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The cliff on the western side of the Thingvellir rift reveals a section through the layer-cake stack of successive lava flows that accumulated before active rifting began. |
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As the two sides of the Thingvellir rift moved apart during plate spreading, a large block on the western edge of the valley subsided and rotated, tilting the once-level strata so that they dipped into the valley. The flag pole in the distance towards the north lies on Logberg. |
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Looking eastward across the Thingvellir rift valley from the North American side, the faults on the European side appear as dark, linear cliffs, some marked by snow patches. The rectangular slab in the foreground is a marker on Logberg, the site of the Althing. Here, Viking leaders spoke to their followers assembled on the valley floor below. |
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Steam rises from several geothermal wells drilled into the valley floor at the south end of the Thingvellir rift. Hengill, an old but still intermittently active volcano, sits in the distance. |
A half-hour flight from Reykjavik city airport takes you to Heimaey, the largest of the 15 islands that make up Vestmannaeyjar (Westmann Islands), south of the mainland. These islands are part of some of the newest geological development in Iceland and include Surtsey, a new volcanic island created by submarine eruption lasting from 1963 to 1966. They are in a northeast-southwest trending belt of recent volcanic activity that includes the volcano Hekla. Some geologists believe that this belt may be a new spreading center, parallel to the local plate boundary, but about 100 km to the east within the European plate. The plate boundary extending southeast from Reykjanes peninsula is asymmetric, with the North American plate moving faster than the European plate. The extra motion on the European side is probably made up by spreading in the new rift zone.
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Viewed to the north from halfway up the slope of the dormant volcano Helgafell, the eastern end of Heimaey lies buried under black basalt. Lava flowed towards the northeast when the northern half of Eldfell collapsed. The remains of several ancient volcanoes, now severely eroded by the sea, provide a protective wall for the village harbor. |
In the early hours of January 22, 1973, the citizens on Heimaey were awakened to the eruption of a new volcano, afterwards called Eldfell. Eldfell formed on the northeastern flank of Helgafell, a dormant volcano to the south of the town. Black ash and lava poured out of the central crater, covering nearby homes.
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Half buried under Eldfell's ash, a home lies abandonned. Grasses and wild flowers have taken root on the new earth. |
The most extensive damage occurred when the northern side of the new volcano collapsed, spreading lava and debris to the northwest and northeast. With the help of equipment from a local military base, the townspeople sprayed sea water on the advancing lava flow when it threatened to cut off the entrance to the harbor. By the time the eruption had finished, the debris buried about one-fifth of the town, added several square kilometers to the size of the island, and improved the quality of the harbor. On that first night, all five thousand inhabitants were evacuated and no lives were ever lost.
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The harbor entrance at Heimaey, once threatened by the advancing blocky lava, now provides even more protection from the Atlantic waves. |
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Beside the harbor entrance at Heimaey, a water tank sits, partly crushed by the weight of blocky lava. |
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Steam rises from the still-hot ash covering the remaining southern half of new volcano Eldfell, Heimaey. |
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Workmen, with their trucks and equipment, are enveloped by steam as they drill into the hot ash of Eldfell, Heimaey. Exhaust vents from numerous geothermal wells appear in the distance. |
Iceland is a land of extreme contrasts, from a vigorous, lively city life to stark, barren landscapes, mountain glaciers, and the ever-present threat of natural violence. You can see them all on day outings. And you have the added thrill of standing on two plate boundaries where new crust is forming, slowly, fitfully, relentlessly, mindless of the cares and concerns of the life that clings to its surface.
| Icelandic | Pronunciation |
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| Drekkingarhylur | Drehkkingarhilur, with both h's pronounced and a trilled r as in Scottish and Spanish |
| Heimaey | Haimi, rhyming with high |
| Hekla | Hehkla, where the second h is aspirated |
| Keflavik | Kehblavik, where the h is not pronounced |
| Oxara | Oxarau, with a trilled r |
| Reykjanes | Reykyaness |
| Reykjavik | Reykyavik |
| Thingvallavatn | Thingvadlavahtn, with an aspirated h in the last syllable. |
| Thingvellir | Thingvedlir |
| Vestmannaeyjar | Vestmanniyar |
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