For geologists, an active volcano is one that has had at least one eruption in the last 10,000 years. But in Iceland we even observe ones that had their last eruption only 10 or 20 years ago. That’s why Iceland is a great place to learn about volcanoes and the effects of their life.
Volcanism is the totality of processes involved in the eruption of magma, gases and steam onto the Earth’s surface. The effects of volcanism, which can be easily observed in Iceland, mainly include volcanic mountains, lava fields, exhalations, geysers and thermal springs. Earthquakes and glacial floods are also effects of a slightly different kind. In this article, we will look at just all of these effects of volcanism.
Volcanic ashes are a very important product of volcanic eruptions. They are what paralyzed air traffic in 2010. (after the eruption of Eyjafjallajokull). However, what stays with us for a long time after volcanic eruptions is lava.
Lava is divided into two large groups depending on its chemical composition: acidic lava and basic lava. In turn, depending on the magma’s viscosity and gas content, so-called block lava and visceral lava are distinguished.
Acidic lava is very rich in silica (SiO2) and viscous. It flows lazily down slopes and often takes much of the rock material it encounters with it. The rocks that form from it are light and usually brightly colored. Characteristic examples are, for example: rhyolites or porphyries, such as we can see in Landmannalaugar or Kerlingarfjoll.
Rhyolite rocks in Landmannalaugar
Bardarbunga volcano lava extent [13]
Gases that failed to escape from the lava masses leave behind characteristic bubbles. These make the lava light, rough and often crumble as it cools. It is called block lava. In Iceland it is apalhraun, and in Hawaii, for example, its name is aa. If the lava doesn’t have as many free gas spaces, it is smooth and shiny and is called visceral lava; in Iceland: helluhraun, and in Hawaii, for example, pahoehoe.
Examples of lava apalhraun and helluhraun (Fraedrich, 2018)
Pumice is also a characteristic type of rock that forms when a volcano erupts. It solidifies from the ejected lava, which is hot but also very rich in gases. This makes pumice very light because it has a great deal of free space in its structure. Pumice is heavier than ash that is why it falls first, which means it always accumulates at the bottom of the ash lids. It is very interesting that due to its porosity it holds on to water. That’s why, for example, pumice from Japanese volcanoes sometimes flows all the way to Hawaii!
Pumice landscape on the F26 road (full color photo!)
Another interesting form that lava sometimes takes is a glaze that looks almost like black glass – this is obsidian. This unique form of lava requires very special conditions for its formation: the lava must be cooled very rapidly and must not have time to solidify. This happens, for example, when heated lava comes into contact with water. Obsidian has a glassy luster and a characteristic shell-like break. It is a rock so intriguing that it often appears in fantasy literature. In Game of Thrones, it was known as dragonglass and was the best weapon against white wanderers and the undead… In The Lord of the Rings, on the other hand, obsidian was used to make the indestructible tower of Orthank in Isengard, where Saruman lived.
Obsidian
Another very interesting and extremely impressive form of lava solidification is the so-called columnar (thermal) blow. Its characteristic product is basalt columns, looking as if the rock was divided into regular vertical columns of polygonal (six, five or quadrilateral) cross-section. This kind of form is formed in the last stage of lava cooling. Cracks are formed perpendicular to the cooling surface due to tensile stresses, which in turn are created by the shrinkage of the lava during solidification. They form best when the cooling is uniform, very slow, and the lava is homogeneous (that is, usually basaltic). Such pillars can be found quite often in Iceland – for example, on the beach of Reynisfjara, by the rocks of Borgarvirki, at the canyon Studlagil or by the waterfalls Litlanesfoss, Svartifoss or Aldeyjarfoss. Such pillars were also the inspiration for the shape of Reykjavik’s largest church – Hallgrimskirkja.
Basalt columns in Studlagil Canyon
Volcanic activity is inevitably accompanied by fumes of gases and vapors called exhalations. They are emitted not only during the eruption itself, but also before and after it. There are three such forms: fumaroles, solfataras and mofetas. The main criterion for distinguishing them is the temperature of the escaping gases and vapors. During an eruption, fumaroles are formed closest to the volcano, followed by solfataras and, at the very end, mofets.
Video: Fumaroles in Hveravellir.
Fumaroles are the hottest, and can range from 200 ºC to as high as 1,000 ºC. Their main product is steam, carbon dioxide, iron, chlorine and sulfur. Often you can also find in the composition of their “fumes” hydrogen sulfide (a noxious gas with a characteristic smell of rotten eggs), hydrogen chloride (which, when combined with water, forms hydrochloric acid) and hydrogen fluoride (which, together with water, also forms hydrofluoric acid, which is very dangerous to humans). Fumes of this type occur near craters in active volcanoes. Being in a place where these with harmful products are present is very dangerous for most living organisms, including humans.
Another type of exhalation is solfataras. Their name comes from the Italian language, where solfa means sulfur. This comes from the fact that with solfataras, so-called native sulfur can be formed. Solfatars are fumes with moderate temperatures – from 100 ºC to 200 ºC. Their main product is superheated steam and small amounts of hydrogen sulfide and carbon dioxide. Due to the fact that their temperature is no longer so high, they occur near dormant or extinct volcanoes.
Mofets are the coolest of the exhalations with temperatures below 100 ºC. They are composed mainly of carbon dioxide and occur farthest from the craters of dormant or extinct volcanoes, where temperatures are no longer as high.
Scientists while measuring the mass of steam from a small exhalation (Fridriksson, 2006)
Geysers are also a spectacular but quite rare manifestation of volcanism. These are springs that periodically eject water, steam and sometimes rock material into the air. They are typical of very young volcanic activity and are known mainly from Iceland, the American Yellowstone, New Zealand and Kamchatka. Some of them may erupt once a year (or less frequently), while others may even erupt every few to tens of minutes! “Godfather” of all geysers in the world, is Geysir, located about 75 km as the crow flies from Reykjavik.
Strokkur geyser eruption
Despite the increased pressure, thanks to the consistently high temperature of the volcanic rocks, the water eventually exceeds the boiling point and bubbles of steam form in it. The small bubbles merge into larger ones and raise the water column slightly, partially ejecting the water. This causes a sudden drop in pressure at the bottom of the geyser and a corresponding drop in boiling point. The water, which has been constantly heating up to, say, 150 ºC, now suddenly finds itself at a point where its boiling point is “only” 110 ºC or 120 ºC. As you can easily guess at this point, a huge amount of water is boiling extremely rapidly. Huge amounts of steam are released, which in turn causes a spectacular explosion – the water above the exploding steam flies high into the air.
Today Geysir itself erupts irregularly and low, but in the 19th century eruptions were recorded in which it ejected water as high as 120 meters. Tourists in Iceland today tend to view the slightly smaller geyser Strokkur, located right next to Geysir, which erupts only at 15-20 m, but regularly every 8 to 10 minutes… The results are absolutely mind-blowing 🙂
Video: How the Strokkur geyser works (and how it explodes!).
Another companion to volcanic activity are thermal springs (also known as hot springs, thermae or thermae). They occur in areas of active or recently extinct volcanic activity. Hot springs are formed from surface water that, through permeable layers or fissures, seeps deep into the earth where it warms at a certain depth. It then seeks the easiest outlet, which is most often a fault, and comes to the surface under pressure. This includes all springs whose temperature of the outflowing water is higher than the average annual temperature in the area, and those whose temperature is consistently higher than 20 ºC.
In Iceland, there are a great many bathable thermal springs, that is, those where the temperature at the outflow does not exceed 35 ºC. Where the spring gives a higher temperature, people often find ways to mix it with cold water and get a nice, pleasant hot bath. Examples include Landmannalaugar or Hveravellir. By contrast, in large pool and spa complexes, of course, everything is under the careful control of technology. Give the Icelandic climate, the hot springs offer a very nice change and a chance to relax during or at the end of a day.
Thermal pools and SPA: Blue Lagoon
The continuous persistence or proceeding of tectonic and volcanic processes in Iceland also results in seismic effects, or earthquakes. These phenomena are tracked by The Icelandic Meteorological Office (IMO). In a way, it is the equivalent of the Polish IMiGW, but due to the nature of the country it also tracks volcanic eruptions, lava flows, earthquakes, volcanic floods and other effects of the island’s volcanism.
However, there is no need to worry – the vast majority of them are very weak tremors. They have a strength, or so-called magnitude, of less than 1.0, and often even referred to as 0.0. So these are shocks perceptible only to specialized apparatus, and associated, for example, with the movement of lava in underground chambers of volcanoes. Human-sensible tremors – those with a magnitude above 3 – occur in Iceland “only” about once a month. However, most of them take place in uninhabited areas, some even in the ocean surrounding the island. The result is that they, too, are usually not felt by people.
Strong quakes – with magnitudes above 6 – usually occur about once a decade [12]. The most recent such quake occurred on May 29, 2008, near the town of Selfoss in the south of the country. The tremor was clearly felt also in Reykjavik, 50 km away. No one was killed as a result of the quake, but 30 people were injured, and many farm buildings in the Selfoss area were damaged.
Statistics suggest that since the last such quake occurred 12 years ago, and they occur on average every 10 years, another one could happen soon. However, while sometimes two strong quakes occur in the same year (e.g., 2000), there could just as well be a 40-year gap between such events (e.g., 1929 – 1968). Therefore, there is no need to postpone the trip until “after the next big earthquake.” After all, it might just as well happen later this year as in 20 years or more. It’s just that when going to Iceland we have to be a bit lucky 🙂
Any flood is, of course, a natural disaster and almost always entails a lot of damage. However, compared to a volcanic eruption, it may seem an unlucky event, but not a dramatic one. Also, its special case – a glacial or glacial flood – does not sound particularly terrible. The English equivalent of this name – GLOF (glacial lake outburst flood) – or Icelandic jokulhlaup also do not carry some particularly frightening emotional charge.
Nothing could be further from the truth. Glacial floods can be a massive disaster, the force of which is hard to imagine.
Glacial flooding owes its catastrophic nature to the fact that the outflow of water is usually stopped by natural barriers in the first phase. This can be a (not yet melted) glacier wall or a moraine or other earthen embankment. Lava pouring out of the volcano melts the ice, but the ice does not immediately flow down. It accumulates in a natural reservoir, and only when the walls of this reservoir break does the water pour out. But then it doesn’t do it slowly – such a flood is already absolutely catastrophic.
The most recent example of such a flood in Iceland is the jokulhlaup of the Grímsvötn volcano in 1996.
In early October 1996, an eruption on the Vatnajökull glacier melted about 3 km3 of ice. The resulting water collected in a subglacial reservoir in the Grímsvötn caldera, the surface of which was about 1,500 meters / 1 mile above sea level.
On November 4, 1996, at about 9:30 PM, the ice wall of this reservoir began to crack. At 7:20 AM the following day, a flash flood occurred 50 kms away at the eastern face of the Skeiðarárjökull outflow glacier. […] In the later hours of that day, the flood gradually covered more areas to the west, along the glacier front located at an altitude of about 100 meters above sea level.
By 3:40 PM floodwaters were leaking from almost the entire 20-kilometer stretch of the glacier front. […] The two main channels through which the flood waters flowed – Gígjukvísl and Skeiðará – at their peak reached flow rates of 33,000 m3/s and 23,000 m3/s, respectively.
Fifteen hours after the flood began in the glacier’s headwaters, the combined maximum flow velocity exceeded 50,000 m3/s [ca. 65,500 cubic yards per second], making these rushing streams of water the second largest river in the world at that point.
Beyond the glacier, an area of 750 km2 [290 sq miles] was flooded. The shoreline advanced as much as 800 meters [880 yards] from the mouth of the Gígjukvísl River. This created a new land area of about 7 km2.
The jökulhlaup on Skeiðarársandur…; Oddur Sigurðsson et al.; [10]
On Road 1, about 3 km south of Skaftafell and the waterfall Svartifoss we can still see the remains of the bridge over the Skeiðará River, which stood there until that flood… The bridge’s huge iron levellers bent like plasticine give a very vivid idea of what power a glacial flood can be. Not only is lava a powerful “weapon” of volcanoes….
Skeidara River bridge destroyed in the 1996 glacial flood
If you’re interested in the topic of the effects of Iceland’s volcanoes, be sure to also read our articles on how volcanoes form and function: Iceland’s Volcanoes, which eruptions we count as the biggest volcanic eruptions in Iceland and why, and about how Iceland itself was formed in the first place and why there are so many volcanoes in Iceland: How Iceland was formed – the geology of the island in a nutshell.
If you want to see the most interesting volcanoes that are easy to see on a trip to Iceland, take a look at the index of sites on the subject: Iceland’s most interesting volcanoes.
