Iceland’s Golden Circle is a popular tour through three of Iceland’s biggest attractions near Reykjavik. It’s an easy way to see some of the most dramatic scenery during a short visit. Some tour companies even operate directly out of Keflavik airport to serve tourists during flight layovers. The tour is also a quick showcase of the geological features which make Iceland unique.

Geological background: the skin and muscle of the Earth

We live on the Earth’s skin, which is called its crust. On the continents, the crust has an average thickness of 30km. That’s like having more than three Mt. Everests under your feet. It’s an enormous amount of rock by human standards, and if you live anywhere but Iceland[1] you can go your entire life without sensing anything underneath. 30km, however, is tiny compared to the 6371km diameter of the Earth. The Earth’s crust has roughly the same proportions as the skin around an elephant’s waist. The Earth’s muscle is hidden underneath its crust. This rock is denser and hotter than the crust. It moves with massive momentum and pulls the crust along with it. Currently, the Americas are being pulled away from Africa and Europe. On any map of the ocean floor, you can see a long ridge running the length of the Atlantic. At this ridge, the ocean floor is separating, and material from deeper inside the Earth is filling in the rift. The mid-Atlantic ridge runs directly across Iceland (red line in the image below). The rock from inside the rift is called basalt. It’s a dark, dense rock found in many volcanic areas and all of the seafloor. It typically forms in volcanic eruptions and spreads away from its source in flat planar layers. These layers aren’t usually thick enough to build islands from the bottom of the sea, but in Iceland they had help. Iceland has a second source of volcanism called a hot spot. For currently unexplained reasons, hot material from inside the Earth jets upwards. It erupts in volcanoes when it reaches the surface, and in time these grow into basalt islands. The most famous hot spot is Hawaii. Under Iceland, the combined output of the rift and the hot spot built an island on a spot where the land itself is being torn apart.

Golden Circle 1: Þingvellir and the mid-Atlantic Rift

Our tour bus pulled up to Þingvellir (Thingvellir) on an uncommonly sunny afternoon with spots of March snow still on the ground. Þingvellir is one of the most dramatic sites of the rift, and its rough, vertical walls are truly unique. We were too stunned to absorb everything on our brief tour stop, and returned to camp in another of the National Park at the end of our trip. Many of the deeper rifts are full of water, making their depths impossible to guess. Their steepness is remarkable. In one place, I stepped over a narrow gap, then turned around and dropped in a heavy pebble. It was three seconds before I heard the splash.

Golden Circle 2: Gulfoss

The tour bus drove on, and our guide entertained us with Icelandic myths and stories of terrible trolls who ate misbehaving children in the night. I stayed pressed up against the window watching the cliffs and terraces that we drove past. In the introduction, I explained that basalt usually forms in flat layers after a volcanic eruption. Between lava flows, these layers are often covered by volcanic ash, tuff, or unconsolidated cinders called tephra. These materials are far softer than basalt. If a river erodes through a layer of basalt into soft tephra, it can continue horizontally without resistance through the tephra until it erodes the next basalt block. The falls were covered in frozen spray during our March visit, but it was warm enough for liquid mist to make a rainbow. On the right bank the ice highlights five distinct layers of basalt. The river has broken these into steps seen on the left.

Golden Circle 3: Geysir

Of course, you can’t have as much volcanism as Iceland does without some heat. After visiting frozen Gulfoss, we made a final stop at the boiling springs of Geysir. These springs are one of the more visible examples of Iceland’s geothermal resources. In addition, Iceland has many hot springs. Some are open to swimming, some are tapped for their power. As of 2010, over one-quarter of Iceland’s power is geothermal, as well as 87% of building heating systems. Many houses in the countryside have private pipes to bring in hot water for heating. The Strokkur geysir is very well-behaved. It goes off every five to ten minutes. Great Geysir itself has been dormant since an earthquake in 2010. The surrounding area is full of smaller water features and hot mud pots, such as the adorably-named ‘Litli Geysir’.