Many of the coolest things about Iceland is the water, fire and earth.
Iceland! Home to the original Geyser, the Blue Lagoon, and Eyjafjallajokul: a volcano whose explosion was so colossal it halted air traffic for days and whose name is so unpronounceable it befuddled news reporters for much longer. The unusual geology of Iceland is a huge part of its charm. At times awe-inspiring, haunting, mesmerizing, or simply unusual there is nowhere else on the earth that looks quite like it.
The reason is that Iceland is geologically one-of-a-kind. The Mid-Atlantic Rift runs right through the heart of the island, bisecting it in a laterally expanding and gently curving line from Reykjavik in the southwest to Húsavik in the northeast. The island is the highest point in the ridge between the Atlantic and European tectonic plates. As the plates move away from each other, magma from the earth’s core wells up in-between, creating a sub-oceanic mountain chain like a scar bisecting the seafloor.
Iceland is also situated above a magma plume, or hot spot: a glob of extra buoyant magma that finds its way close to the surface, punching the landmass above it skyward. Iceland is ever growing, both horizontally as the plates diverge and vertically as the plume beneath the earth’s surface pushes its highest peak, Hvannadalshnjukur, even higher. Many of the coolest things about Iceland have to do with these two magma sources. They are elemental to Iceland, effecting water, fire and earth.
The particular geology of Iceland has created some of its most popular water-based tourist attractions.
The Blue Lagoon is the most well-known hot spring in Iceland. Conveniently located between the international airport in Keflvik and Reykjavik it is an easy stop over for tourists. While there are many naturally occurring hot springs in Iceland, the Blue Lagoon is actually man made. On a clear day, the steam clouds emitted by the adjacent Geothermal Plant are plainly visible from the highway. In fact, we almost made a wrong turn into the plant on our drive! The plant drills about 2,000 meters into the earth, releasing the superheated, mineral rich waters to produce electricity and hot water for the surrounding neighborhoods. Naturally occurring hot springs tend to be smaller, with the water coming to the surface through artesian springs or natural vents.
The water in the Blue Lagoon is between 98-104 degrees Fahrenheit year round. It maintains that temperature because (you guessed it) the magma plume superheats the ground water beneath the island. All ground water picks up minerals by eroding the surrounding rock, but the super-heated water of the Blue Lagoon is able to dissolve and hold more minerals in suspension than average ground water. The Blue Lagoon is particularly silica rich, giving the water its blue color (the water is actually milky white in small amounts, but the way the dissolved silica refracts sunlight makes it appear blue). The white crust you can see at the edges of the pool is re-solidified silica coating the stone. Other minerals dissolved in the water include sodium, potassium, calcium, magnesium, carbon dioxide, sulphate, chlorine, and fluorine. No wonder it is so good for you!
Geysers are very rare natural phenomena. There are fewer than 2,000 known geysers in the world, with a majority of them in Yellowstone National Park. Of those 2,000 geysers, around 500 are considered active. Iceland is home to the original namesake, Geysir, located close to Reykjavik. It is a vital stop on the Golden Circle, a close grouping of several natural phenomena popular with tourists. Geysir itself is now almost inactive. It simmers and bubbles quietly, but its rare explosions are impossible to predict.
An Icelander I talked with told me that explosions had been induced in the past by throwing common household detergent soap into the pool to celebrate important dates in Icelandic history. I thought, of course, this could not be true, but according to my research he was telling the truth. Apparently adding soap lowers the surface tension of the molecules within the water, making it possible for it to boil at a lower temperature. Pretty cool if you ask me, though I would not recommend you give it a try if you are ever standing next to Geysir. Inducing an eruption this way damages the geyser, making it less likely to erupt naturally in the future. Let’s just say breaking a local landmark is probably not a great way to make a bunch of new Icelandic friends. Although Geysir is inactive, Strokkur, a geyser directly adjacent whose name translates to “The Churn”, is still active and fairly regular, exploding every 10-20 minutes.
Geysers are rare because they require very specific geological circumstances. First and foremost is superheated geothermal water. For all of Iceland, that is a “check!” Next, they need very specific underground “plumbing.” There is a lot about geysers that is still a mystery to geologists but the basics are easy to understand. Deep beneath the earth’s surface, groundwater interacts with the heat coming off the magma. In some places, the water forms a column. The water towards the bottom and middle, closest to the magma, becomes superheated while the water at the top of the column remains relatively cool. This cool water on top acts as a “cap”, preventing the super-hot water at the bottom from actually boiling. Eventually the heat transfer from the magma reaches the top of the water column and the cool “cap” reaches boiling temperature. When this happens the entire water column boils at the same time, releasing bubbles of gas explosively. If conditions are right, the now boiling water will reach the surface through the underground “plumbing” in an explosive column of water and steam.
Sometimes, if the minerals dissolved in the super-heated ground water are silica rich, they can leave deposits on the surrounding “plumbing” as the water column explodes. Consecutive explosions will turn these deposits into a stone called Geyserite, essentially lubricating the underground plumbing, making it easier for the super-heated water to follow the same path to the surface each time. The formation of Geyserite, along with the predictable nature in which water boils and the constant heat of the magma plume, can lead to extremely predictable Geyser explosions. This is the case with Old Faithful in Yellowstone National Park.
There are a lot of variables that determine the way that magma reaches the earth’s surface. Depending on the conditions, different types of volcanoes can be created.
The relatively “safer” volcanos are called shield volcanoes. In these volcanoes, the magma has a low viscosity, that is to say it flows easily over the earth’s surface. The reason is that the magma in shield volcanoes is mafic. All magmas, and all rocks that magma creates as it cools, are made out of mafic and/or felsic materials. The easiest way to tell the difference is color: mafic materials are dark and felsic are light in color. Mafic magmas are rich in physically heavy, dark colored elements, such as iron, calcium and sodium. Felsic elements are physically lighter and closer to white in color. They include elements like silica, oxygen, aluminum and potassium. If mafic magmas are allowed to cool slowly, they can create a range of rocks. However, when extruded from a volcano, and therefore forced to cool very fast, it will not have time to sort out the darker, heavier materials, and will create only dark, heavy (mafic) rocks.
This is the case with shield volcanoes. Rather than explode violently, they “leak” a dark, slow moving lava that rolls down the side of the volcano, spreading thinly across large areas until there is no more lava. Thus shield volcanoes are relatively short, made up of successive, thin layers of black rock.
Strata volcanoes are the ones that erupt violently. They are the result of more felsic magma sources. Felsic lava acts very differently than mafic lava. It has a high viscosity, meaning it flows slowly, clumping and forming rocks easily. It can sometimes clog the top of the volcano, forming a “plug” on the magma chamber below the mountain. This builds pressure inside the mountain until the force of the gases emitted by the magma exceeds the strength of the bonds between the elements that make up the rocky “plug”. Strata volcanoes also tend to have more water mixed into their felsic magma chambers. Adding water to magma makes the eruption more volatile. Extra water means extra gas (steam) is created when the water boils. This adds to the pressure within the volcano. When strata volcanoes do explode, they can literally blow their top, spewing light colored, fast cooling rocks high into the atmosphere. This is exactly the case with Eyjafjallajokul. When that volcano erupted, it threw volcanic dust so high into the atmosphere that it became unsafe to fly planes through the cloud. Strata volcanoes are taller with steeper slopes than shield volcanoes. This is again due to the highly viscous property of the rocks that they create.
Both shield and strata volcanoes exist in Iceland. Now that you know the difference, use a critical eye when you look around. Is the mountain you are looking at tall and pointy with a blown off top? Maybe it is a strata volcano. Is it kind of short and surrounded by large fields of black rock? Maybe it is a shield volcano.
Whether created by lava extruding from a volcano or magma slowly cooling beneath the earth’s surface, Iceland has the raw materials to continuously create new earth.
As I talked about above, large parts of Iceland are covered in lava fields. These occur when slow moving, dark, heavy mafic lava seeps out of a volcano and flows wherever gravity takes it until the original magma chamber is empty. These lava fields can show clues of their original source if you look carefully. On my travels, I heard a lot of people remarking on the ripples in some of these lava flows. It almost looks at if water had been petrified, frozen while in motion. This is a telling characteristic of Pahoehoe flows. Named in Hawaii, where they are common, Pahoehoe flows are formed by only the lowest viscosity (easiest flowing) types of lava. The lava is slow to solidify, acting kind of like water, hence the ripples. Pahoehoe lava can also form “toes,” this is when a gas bubble from beneath the surface rises to the top, deforming the smooth surface of the flow and hardening into a pillar shape. So, are the rocks you are looking at relatively smooth on top with signs of rippling and vertical pillars? Maybe it is a Pahoehoe flow!
But what if the rocks you are looking at do not look smooth and rippled? What if, instead, they have a choppy surface that looks like it might shred your sneakers? Well, then maybe it is an A’A’ Flow. Also named in Hawaii, A’A’ Flows come from more felsic magmas. They will always have a choppy, deformed surface, a little like poorly mixed cement.
I found the basalt columns in Iceland particularly beautiful. Tall, slender, hexagonal pillars, fractured and falling down, they seemed like the ruins of a gothic church or a haunted forest of petrified trees. Basalt columns are the result of lava cooling slowly, normally in pools that are contained in a depression. As the basalt cools, it shrinks and cracks. This is true of almost all materials (except water) as they change from a liquid to a solid. Think of the cracks that form in mud on a hot day.
The same is true of basalt lava as it cools to form basalt rock. The hexagonal tube shape is due to the way the elements bond within the rock itself. The elements within the basalt form stronger bonds vertically than horizontally. Thus, as the lava cools and cracks, it will be more likely to break along the weaker horizontal bonds then the stronger vertical bonds. If the pool cools slowly and evenly, the cracks will be in “perfect” hexagonal patterns. If it cools unevenly they will form uneven geometric shapes. As the rest of the lava cools, farther and farther away from the surface of the lava pool, the fractures will propagate downward from the surface: breaking along the weaker horizontal bonds, maintaining the stronger vertical ones, and continuing the original geometric pattern. As the columns are exposed to weathering, they break off of the original block according to their pre-existing fractures.
Now that you know the basics, go out there and astound your travel buddies with your geological knowledge! Big shout out to my friend Jake Roberson for all his helpful geological knowledge. I really enjoyed our nerdy conversations. You rock! (pun intended.)
Photos: Hillary Kurland
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