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Imaggeo on Mondays: A volcanic point of view

Imaggeo on Mondays: A volcanic point of view

It’s not every day that you can peer into a volcano, much less gaze out at the sky from the inside of one. The Algar do Carvão, or “the Cavern of Coal,” is one of the few places on Earth where you can explore the underground reaches of a volcanic site.

The volcanic pit is found on the island of Terceira, part of the Azores archipelago. This collection of islands is an autonomous region of Portugal, located in the Atlantic Ocean about 1800 kilometres west from the Portuguese mainland. The archipelago is an especially volcanic hotspot, situated on the border of three major tectonic plates: the North American, Eurasian and African Plates.

The Algar do Carvão is essentially an ancient lava tube, made up of a volcanic chimney, about 80-90 metres deep, which then opens up into secondary magma chambers. The chimney formed first roughly 3,200 years ago, in the wake of a volcanic eruption. Then a second eruption, occurring in the same spot 1,200 years later, created many of the magma chambers seen today.

A profile of the Algar do Carvão, based on a similar cutaway produced by “Os Montanheiros,” (Credit: Ruben JC Furtado / Wikimedia Commons)

Despite what the cavern’s title suggests, the volcanic site is not a source of coal, but rather named for the walls’ dark black, ‘sooty’ colour. The volcanic pit is actually better known by geologists and cave enthusiasts for its source of silica-rich stalagmites and stalactites, a feature not commonly found in this region. Scientists have hypothesized that the structures’ silicate composition could have come in part from the volcano’s past hydrothermal activity or its population of diatoms, microorganisms which contain silica in their cell walls.

As you can see from the lush flora featured in today’s photo, the Algar do Carvão is teeming with life. Vegetation blankets the mouth of the cone structure and many animal populations thrive in the cavern environment. The volcanic pit is also home to several species found only on the Azores islands, like the troglobian spider Turinyphia cavernicola and the Terceira Island scarab Trechus terceiranus.

References

Daza, D. et al.: Isotopic composition (δ¹⁸ O y δD) of silica speleothems of the Algar do Carvão and Branca Opala volcanic caves (Terceira Island, Azores, Portugal), Estudios Geológicos, 70, 2, 2014.

Borges, P. A. V., Carlos Crespo, L., Cardoso, P.: Species conservation profile of the cave spider Turinyphia cavernicola (Araneae, Linyphiidae) from Terceira Island, Azores, Portugal, Biodiversity Data Journal 4: e10274, 2016.

Nunes, J.C., J.P. Constância, M.P. Costa, P. Barcelos, P.A.V. Borges & F. Pereira: Route of Azores Islands Volcanic Caves. Associação Os Montanheiros & GESPEA (Ed.). 16, 2011.

Algar do Carvão, Associação Os Montanheiros

Natural Monument of Algar do Carvão, 2011 Regional Secretariat for Agriculture and Environment, Governo dos Açores

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 http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Iceland’s original birch forest

Imaggeo on Mondays: Iceland’s original birch forest

Iceland is a country of dramatically rugged landscapes. The region is home to sweeping valleys and mountain ranges, dotted with lava fields, large glaciers, hot springs and impressive waterfalls.

The territory is also notoriously treeless. As of 2016, forests only made up 1.9 percent of Iceland, according to the Icelandic Forest Service. However, about a thousand years ago the country’s landscape was far more vegetated, and remnants of Iceland’s original woodlands still exist today.

It is a common misconception that Iceland is too cold to sustain a forest. “On the contrary, it has been observed that, at the time of human settlement, birch woods and scrubs have covered large parts of Iceland,” said Marco Cavalli, a researcher at the Research Institute for Geo-Hydrological Protection in Italy and the photographer of today’s featured image. In fact, Iceland’s fossil evidence suggests that, before human settlement, 25-40 percent of the island was dominated by woodlands and thickets.

When humans migrated to the island about 1100 years ago, much of Iceland’s natural forests were chopped down to make way for fields and pastures. In the centuries following human settlement, intensive sheep grazing and volcanic eruptions prevented forests from regenerating. By 1950, less than one percent of the country was covered by trees.

Iceland’s vegetation-devoid state presents an environmental problem to local Icelanders, since the lack of trees, combined with the island’s volcanic activity, has left the land vulnerable to severe soil erosion. Since the soil conditions prevent vegetation from taking root, erosion has limited farming and grazing efforts. Iceland’s loose soil and strong winds are also responsible for damaging sandstorms.

Soil conservation and forestry services have made substantial efforts to repopulate the Icelandic environment with trees, just about doubling Iceland’s tree cover since the mid-20th century. However, there is still a long road ahead to reach the Icelandic Forest Service’s goal to see 12 percent of Iceland afforested by 2100.

This picture was taken by Cavalli while on a field trip in Rangárvellir, a southern region of Iceland near Gunnarsholt, the headquarters of the Soil Conservation Service of Iceland (SCSI). The workshop focused on the area’s severe degradation from both human activities and natural causes, and efforts to restore the ecosystem.

During the workshop he spotted this particular grove of dwarf birch trees. “I was impressed to see a small remnant patch of the Icelandic original birch forest resisting all these adverse conditions,” said Cavalli. “I would say this is a good example of nature fighting to survive.”

References

Forestry in a Treeless Land, Icelandic Forest Service

Changes in vegetation cover from the time of Iceland’s settlement, Icelandic Institute of Natural History

Vikings Razed the Forests. Can Iceland Regrow Them?, The New York Times

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 http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: White mist on White Island

White Island, also known as Whakaari, is an active stratovolcano off the coast of New Zeland’s North Island, nested in the northern end of the Taupo Volcanic Zone. Much of its activity is made up of bubbling mud pools and steamy, sulphurous clouds from fumaroles like the one below – sights that attracts many a tourist to the marine volcano.

“Geothermal energy live” by J. Florian Wellmann, distributed via imaggeo.egu.eu.

“Geothermal energy live” by J. Florian Wellmann, distributed via imaggeo.egu.eu.

Over the last 200 or so years, a large part of White Island has been peppered with fumaroles like this one – each releasing a variety of volcanic gasses into the atmosphere. Sometimes, though, the island shows signs of real unrest and when a lot of water comes in close proximity to the hot basalt beneath the surface, it rapidly vaporises, resulting in a steam-driven explosion known as a phreatic eruption. These are not something you want to be close to.  The force of the water sends blogs of basalt into the air, together with ash and other debris, and the eruption produces high velocity volcanic flows that spread out from the point of the explosion. The last phreatic eruption at White Island occurred in October 2013 and resulted in a new layer of mud being deposited across the crater floor.

Step back to take in the view – Crater Bay on White Island. (Credit: Javier Sánchez Portero)

Step back to take in the view – Crater Bay on White Island. (Credit: Javier Sánchez Portero)

GeoNet monitors New Zealand’s volcanoes, White Island among them, so that the authorities can rapidly respond in the event of a disaster. While the volcano isn’t in a phreatic phase, current activity is higher than normal, putting White Island at alert level 1 (on a scale of 1 to 5). You can check out the volcano’s latest activity here – when the sun is up you can see some great images from the volcano-cam, as well as a short and sweet summary of seismic action on the island!

Is the volcano-cam is shrouded in darkness? This footage, which shows some spectacular mud explosions, will make up for it (while you’re behind the safety of your computer screen):

Reference:

Rose, W. I., Chuan, R. L., Giggenbach, W. F., Kyle, P. R., & Symonds, R. B.: Rates of sulfur dioxide and particle emissions from White Island volcano, New Zealand, and an estimate of the total flux of major gaseous species. Bulletin of volcanology, 48, 181-188 (1986).

The EGU’s open access geoscience image repository has a new and improved home at imaggeo.egu.eu! We’ve redesigned the website to give the database a more modern, image-based layout and have implemented a fully responsive page design. This means the new website adapts to the visitor’s screen size and looks good whether you’re using a smartphone, tablet or laptop.

Photos uploaded to Imaggeo are licensed under Creative Commons, meaning they can be used by scientists, the public, and even the press, provided the original author is credited. Further, you can now choose how you would like to licence your work. Users can also connect to Imaggeo through their social media accounts too! Find out more about the relaunch on the EGU website. 

Imaggeo on Mondays: Hekla’s history

Iceland is well known for its extensive volcanism. Situated amid the northernmost part of the Mid-Atlantic Ridge, the spreading centre is a hub of volcanic activity, from Krafla in the north to the young volcanic island of Surtsey in the south.

Simplified geological map of Iceland, showing the country’s larger volcanoes. (Credit: Wikimedia Commons user Pinpin)

Simplified geological map of Iceland, showing the country’s larger volcanoes (click for larger). (Credit: Wikimedia Commons user Pinpin)

Hekla is one of the country’s most active volcanoes – both in terms of erupted material and eruption frequency, and lies at the heart of a 40 kilometre long, 7 kilometre wide volcanic system. This week’s Imaggeo on Mondays features a lava flow in Landmannalaugar, not far from the volcano:

“Lava outflow in Iceland” by Wolfgang Schwanghart, who took this photo at Landmannalaugar in the Icelandic highlands. This image is distributed by the EGU under a Creative Commons licence.

“Lava outflow in Iceland” by Wolfgang Schwanghart, who took this photo at Landmannalaugar in the Icelandic highlands. This image is distributed by the EGU under a Creative Commons licence.

The frequency of Hekla’s eruptions is reflected in its chemistry: long periods between eruptions correspond to the eruption of viscous, silica-rich magma known as rhyodacite, and shorter ones (30 years or fewer) result in the eruption of low-silica magmas, from andesite to basaltic andesite. Hekla’s historic eruptions have always begun explosively, but the magnitude and duration of this explosive period is dependent on the length of time between eruptions – the longer the gap, the more explosive the eruption.

Once the initial explosive phase is over, and the eruption becomes effusive Hekla releases large volumes of lava like the one above. Records show this is the case for all of the eruptions that have occurred during recorded history – the exception being the 1104 eruption, where it is not certain Hekla had an effusive phase.

The volcano has erupted in this pattern at intervals of about 55 years since the 1100’s. That is, until fairly recently. The last four eruptions occurred in 1970, 1980, 1991 and 2000, and may indicate that Hekla may be entering a new phase of activity – one characterised by relatively small, frequent eruptions.

The 1980 eruption of Hekla volcano. (Credit: Wikimedia Commons user Oxonhutch)

The 1980 eruption of Hekla volcano. (Credit: Wikimedia Commons user Oxonhutch)

References:

Gronvold, K., Larsen, G. , Einarsson, P. , Thorarinsson, S. and Saemundsson, K.: The Hekla eruption 1980–1981, Bulletin of Volcanology, 46, 349-363, 1983.

Gudmundsson, A., Oskarsson, N., Gronvold, K., Saemundsson, K., Sigurdsson, O., Stefansson, R., Gislason, S. R. et al.: The 1991 eruption of Hekla, Iceland. Bulletin of Volcanology, 54, 238-246, 1992.

Lacasse, C., Karlsdóttir, S., Larsen, G., Soosalu, H., Rose, W. I., and Ernst, G. G. J.: Weather radar observations of the Hekla 2000 eruption cloud, Iceland. Bulletin of Volcanology, 66, 457-473, 2004.

Thorarinsson, S. and Sigvaldason, G. E.: The Hekla eruption of 1970. Bulletin of Volcanology, 36, 269-2888, 1972.

Imaggeo is the EGU’s open access geosciences image repository. A new and improved Imaggeo site will be launching soon, so you will be able to peruse an even better database of visually stunning geoscience images. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.