Iceland’s rootless volcanoes

Iceland’s rootless volcanoes

Picture a volcano, like the one you learned about in primary school. Can you see it? Is it a big rocky mountain, perhaps with a bubbling pool of lava at the top? Is it perched above a chasm of subterranean molten rock?

I bet you didn’t picture this:

Rootless cones in the Lanbrotshólar district, S Iceland. Created by the 940AD Eldgjá eruption, there are over 4000 rootless cones in this area. Credit: Frances Boreham

You’d be forgiven for mistaking these small volcanoes for a scene from the Lord of the Rings, or maybe a grassy version of the surface of Mars (in fact, these kind of volcanoes do occur on Mars). These, however, are in Iceland and are called rootless cones.

These mini-volcanoes are unusual because they are ‘rootless’ meaning, unlike most volcanoes, they are not fed from the underground. To make them even stranger, they erupted only once and as part of the same event.

This type of volcanism is observed in several places around the world and occurs only in a unique set of circumstances. Despite showing similarities to more traditional volcanoes (like pyroclastic cones), the cones pictured above actually erupted several tens of kilometres from a ‘true’ volcano.

Rootless cones occur when a hot lava flow produced by an eruption travels away from the volcano and meets water. This can be a lake, a river, a glacier or simply a bit of soggy ground. The only criteria are that there needs to be water, and it needs to be trapped. Lava flows are usually at temperatures of over 1000oC and so, when they come into contact with trapped water or ice, its causes a build-up of steam, which can explode violently through the lava forming a rootless cone.

An article, published in the Journal of Volcanology and Geothermal Research in September by volcanologists from the University of Bristol and the University of Iceland, analysed the shape and location of some of these cones to understand more about the environment in which they formed.

These features are found in northeast Iceland in the region around lake Mývatn. The area, 50 km east of the city of Akureyri, is world famous for its beautiful scenery and unusual landscapes.

The volcano responsible for the phenomena is the Þrengslaborgir–Lúdentsborgir crater row which erupted around 2000 years ago. The eruption produced a huge lava flow that covered an area of 220 km2; over 2% of the surface of Iceland. The flow, known as the Younger Laxá Lava, permanently changed the landscape, diverting rivers and damming lakes. After its extrusion from the volcano, the stream of molten rock meandered through different environments including river gorges and wide glacial valleys.

The flow’s diverse 67km journey allowed lead author Frances Boreham and her colleagues, to learn how it interacted with its surroundings. As she explains it, “one of the things that makes the Younger Laxá Lava such a great case study is the range of environments that the lava flowed through.”

Rootless cones do not all look the same and vary greatly in size, from small ‘hornitos’ which are about the size of a small car, to large crater-shaped cones hundreds of metres in size. The scale and complexity of the deposits makes them difficult to study as Boreham explains, “One of the biggest challenges is trying to understand and unpick the different effects of lava and water supply on rootless eruptions. We see a huge variety in rootless cone shapes and sizes, but working out which aspects are controlled by the lava flow and which by the environment and available water is tricky, especially when working on a lava flow that’s approximately 2000 years old!”

From Boreham et al. 2016. “Different types of rootless cone and associated features. a) Scoriaceous rootless cone at Skutustaðir, Mývatn. Cone base is ~100 m diameter. b) Explosion pits (marked with arrows) surrounding a scoriaceous rootless cone near Mývatn. c) Spatter cone at Mý d) Hornito in Aðaldalur, NE Iceland. Map imagery on d ©2017 DigitalGlobe, Google.” Licensed under creative commons.

Despite their beauty, the rootless cones represent a more serious issue. Lava flows are often thought of as quite benign compared to other volcanic hazards like pyroclastic flows. The presence of rootless cones suggests this isn’t always the case. “As far as I know, none of these rootless cones are currently taken into account for lava flow hazard assessments, in Iceland or elsewhere in the world. While not applicable everywhere, wet environments with a history of lava flows, such as Iceland or parts of the Cascades, could be affected and these hazards should be considered in future risk assessments and plans, e.g. by identifying vulnerable property, roads and infrastructure.” said Boreham.

By Keri McNamara, freelance science writer

Keri McNamara is a freelance writer with a PhD in Volcanology from the University of Bristol. She is on twitter @KeriAMcNamara and

Geosciences Column: Using volcanoes to study carbon emissions’ long-term environmental effect

Geosciences Column: Using volcanoes to study carbon emissions’ long-term environmental effect

In a world where carbon dioxide levels are rapidly rising, how do you study the long-term effect of carbon emissions?

To answer this question, some scientists have turned to Mammoth Mountain, a volcano in California that’s been releasing carbon dioxide for years. Recently, a team of researchers found that this volcanic ecosystem could give clues to how plants respond to elevated levels of carbon dioxide over long periods of time. The scientists suggest that studying carbon-emitting volcanoes could give us a deeper understanding on how climate change will influence terrestrial ecosystems through the decades. The results of their study were published last month in EGU’s open access journal Biogeosciences.

Carbon emissions reached a record high in 2018, as fossil-fuel use contributed roughly 37.1 billion tonnes of carbon dioxide to the atmosphere. Emissions are expected to increase globally if left unabated, and ecologists have been trying to better understand how this trend will impact plant ecology. One popular technique, which involves exposing environments to increased levels of carbon dioxide, has been used since the 1990s to study climate change’s impact.

The method, also known as the Free-Air Carbon dioxide Enrichment (FACE) experiment, has offered valuable insight into this matter, but can only give a short-term perspective. As a result, it’s been more challenging for scientists to study the long-term impact that emissions have on plant communities and ecosystems, according to the new study.

FACE facilities, such as the Nevada Desert FACE Facility, creates 21st century atmospheric conditions in an otherwise natural environment. Credit: National Nuclear Security Administration / Nevada Site Office via Wikimedia Commons

Carbon-emitting volcanoes, on the other hand, are often well-studied systems and have been known to emit carbon dioxide for decades to even centuries. For example, experts have been collecting data on gas emissions from Mammoth Mountain, a lava dome complex in eastern California, for almost twenty years. The volcano releases carbon dioxide at high concentrations through faults and fissures on the mountainside, subsequently leaving its forest environment exposed to the emissions. In short, the volcanic ecosystem essentially acts like a natural FACE experiment site.

“This is where long-term localized emissions from volcanic [carbon dioxide] can play a game-changing role in how to assess the long-term [carbon dioxide] effect on ecosystems,” wrote the authors in their published study. Research with longer study periods would also allow scientists to assess climate change’s effect on long-term ecosystem dynamics, including plant acclimation and species dominance shifts.

Through this exploratory study, the researchers involved sought to better understand whether the long-term ecological response to carbon-emitting volcanoes is actually representative to the ecological impact of increased atmospheric carbon dioxide.

Remotely sensed imagery acquired over Mammoth Mountain, showing (a) maps of soil CO2 flux simulated based on accumulation chamber measurements, shown overlaid on aerial RGB image, (b) above-ground biomass (c) evapotranspiration, and (d) normalized difference vegetation index (NDVI). Credit: K. Cawse-Nicholson et al.

To do so, the scientists analysed characteristics of the forest ecosystem situated on the Mammoth Mountain volcano. With the help of airborne remote-sensing tools, the team measured several ecological variables, including the forest’s canopy greenness, height and nitrogen concentrations, evapotranspiration, and biomass. Additionally they examined the carbon dioxide fluxes within actively degassing areas on Mammoth Mountain.

They used all this data to model the structure, composition, and function of the volcano’s forest, as well as model how the ecosystem changes when exposed to increased carbon emissions. Their results revealed that the carbon dioxide fluxes from Mammoth Mountain’s soil were correlated to many of the ecological variables analysed. Additionally, the researchers discovered that parts of the observed environmental impact of the volcano’s emissions were consistent with outcomes from past FACE experiments.  

Given the results, the study suggests that these kind of volcanic systems could work as natural test environments for long-term climate research. “This methodology can be applied to any site that is exposed to elevated [carbon dioxide],” the researchers wrote. Given that some plant communities have been exposed to volcanic emissions for hundreds of years, this method could help paint a more comprehensive picture of our future environment as Earth’s climate changes.

By Olivia Trani, EGU Communications Officer


Cawse-Nicholson, K., Fisher, J. B., Famiglietti, C. A., Braverman, A., Schwandner, F. M., Lewicki, J. L., Townsend, P. A., Schimel, D. S., Pavlick, R., Bormann, K. J., Ferraz, A., Kang, E. L., Ma, P., Bogue, R. R., Youmans, T., and Pieri, D. C.: Ecosystem responses to elevated CO2 using airborne remote sensing at Mammoth Mountain, California, Biogeosciences, 15, 7403-7418,, 2018.

Imaggeo on Mondays: The ash cloud of Eyjafjallajökull approaches

Imaggeo on Mondays: The ash cloud of Eyjafjallajökull approaches

This photo depicts the famous ash cloud of the Icelandic volcano Eyjafjallajökull, which disrupted air traffic in Europe and over the North Atlantic Ocean for several days in spring 2010. The picture was taken during the initial phase of the eruption south of the town of Kirjubæjarklaustur, at the end of a long field work day. Visibility inside the ash cloud was within only a few metres.

The eruption was preceded by years of seismic unrest and repeated magma intrusions. A first effusive fissure opened outside the ice shield of the volcano at the end of March 2010, followed by an explosive eruption in the main crater of the volcano in April 2010.

Iceland was well prepared for the eruption – the rest of the world obviously was not. The region around Eyjafjallajökull is sparsely populated, residents were prepared days before the eruption and the evacuation went smoothly. However, the grain size of the ejected volcanic ash was fine enough so that the unfavourable and unusual wind direction during these days transported the ash all the way to Europe and led to air space closures almost all over the continent.

By Martin Hensch, Nordic Volcanological Center, University of Iceland (now at Geological Survey of Baden-Württemberg, Germany)

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at

June GeoRoundUp: the best of the Earth sciences from around the web

June GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web. 

Major story  

While May’s headlines may have been dominated by the Kilauea Volcano’s recent eruption in Hawaii, the science news world directed its attention to another volcanic event early this month. On June 3, Guatemala’s Volcán de Fuego erupted, sending plumes of volcanic ash several kilometres into the air. The volcano also unleashed an avalanche of hot gas and debris, otherwise known as pyroclastic flows, more than 10 kilometres down the volcano’s flanks onto the surrounding valley.

The Volcán de Fuego has been an active volcano since 2002, however, this latest event has been the volcano’s most violent eruption in more than four decades.

By 23 June, officials reported that the eruption has killed 110 people from surrounding villages, with hundreds more missing or injured.

Both Kilauea and Fuego gained international attention this year, but the two volcanoes exhibit very different behaviours by nature.

Kilauea is a shield volcano, with a relatively gradual slope and a highly fluid lava flow that can travel far distances compared to other volcanic archetypes. While the volcanic eruption’s lava, ash and haze present real threats to nearby communities, very few injuries have been reported.

“Lava flows rarely kill people,” said Paul Segall, a professor of geophysics at Stanford University, to the New York Times. “They typically move slow enough that you can walk out of the way.”

The Fuego volcano on the other hand is a stratovolcano, characterised by a cone-shaped peak built by layers of lava and ash. This type of volcano usually contains more viscous magma, meaning the hot liquid material has a sticky, thicker consistency. This type of fluid in volcanoes “clogs their plumbing and leads to dramatic explosions,” says Smithsonian Magazine.

Stratovolcanoes like Fuego also often release pyroclastic flows. These plumes can be a major threat to human health and make this kind of volcano particularly dangerous. “On its surface, a pyroclastic flow looks like a falling cloud of ash. But if you could peer into the cloud, you would find a really hot and fast-moving storm of solid rock,” reported PBS NewsHour.

Paul Rincon, a science editor for BBC News notes that pyroclastic flows can reach speeds of up to 700 kilometres per hour and are extremely hot, with temperatures between 200 to 700 degrees Celsius.

As of June 17, Guatemalan authorities have officially stopped looking for bodies and survivors. However, some local rescue workers have kept on with their search. 

What you might have missed

Meanwhile this month, in a vastly different part of the world, scientists have uncovered a wealth of new insight into Antarctica and how the region’s ice melts. Some of the discoveries made known are very foreboding while others more uplifting.

Let’s start with the bad news first. A study published this month in Nature revealed that Antarctica is melting faster than ever, and the continent’s rate of ice loss is only accelerating.

The report explains that before 2012 the Antarctic ice sheet steadily lost 76 billion tonnes of ice each year, contributing 0.2 milimetres to sea-level rise annually. However, since then, Antarctica’s rate of ice loss has increased threefold. For the last fives years the ice sheet has shed off 219 billions tonnes of ice each year. This ice loss now corresponds to a 0.6 milimetre contribution, making Antarctica one of the biggest sources of sea-level rise.

The largest iceberg ever recorded broke away from the Antarctic Peninsula in 2017. Pictured here is the iceberg’s western edge. (Credit Nathan Kurtz/NASA)

This record pace could have a devastating impact around the world, the researchers involved with the study say.

“The continent is now melting so fast, scientists say, that it will contribute six inches (15 centimeters) to sea-level rise by 2100,” reports the New York Times.

The articles continues: “’around Brooklyn you get flooding once a year or so, but if you raise sea level by 15 centimeters then that’s going to happen 20 times a year,’ said Andrew Shepherd, a professor of earth observation at the University of Leeds and the lead author of the study.”

On the other hand, one study published this month in Science offers a glimmer of hope, suggesting that a natural geologic process may help counteract some of the Earth’s sea level rise.

A team of researchers found evidence that, in response to losing ice mass, the ground underneath melting ice sheets naturally lifts up, and more substantially than scientists had previously believed. This process could help prevent further ice loss by land locking vulnerable ice sheets.

Scientists say that many ice sheets in the West Antarctic are at risk of collapsing, and furthermore contributing to sea level rise, because they are in direct contact with the ocean. The relatively warm seawater can melt these glaciers from underneath, making these giant frozen masses more at risk of losing a substantial amount of ice.

However, the new research on the West Antarctic Ice Sheet finds that as these ice masses lose weight, the ground underneath springs up, acting much like a memory-foam mattress.

“This adjustment of the land once the weight of the ice has been lifted is known as ‘glacial isostatic adjustment,’” says Carbon Brief. “It is usually thought to be a slow process, but the new data suggests the ground uplift beneath the [Amundsen Sea Embayment] area is occurring at an unprecedented rate of 41mm per year.”

A press release from Delft University of Technology in the Netherlands goes on to say that “the measured uplift rate is up to 4 times larger than expected based on the current ice melting rates.”

While this discovery offers a brighter view to the serious state of Earth’s melting ice, scientists still caution that this natural grounding process may be rendered useless in extreme cases climate change with extensive ice loss.

Links we liked 

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