Eruptions on La Palma, Canary Islands.

Following a marked increase in seismic activity beneath La Palma volcano, on the Canary Island of the same name, authorities on the island began to make plans to evacuate residents from the area in the event of an eruption on 17 September 2021. Two days later, on Sunday 19 September, the volcano began to erupt at about 3.10 pm, with two fissures roughly 200 m long and 200 m apart opening on the flank of the volcano, producing columns of gas and ash that rose to 1.5 and 3.0 km above sealevel respectively, and lava fountains that set fire to nearby forests. Lava began to descend the sides of the volcano at a rate of about 700 m per hour (slow enough to evade at a walking pace), prompting evacuations and causing extensive damage to properties in its path. The volcano produced a vast plume of sulphur dioxide, which reached the coast of Morocco on 20 September, by which time lava flows had reached up to 3 km from the vents and destroyed 166 buildings. Over the next few days, the volcano produced further ash columns, which rose to heights as great as 4.6 km, while the lava spread to cover about 1.54 km², destroying over 350 homes and prompting the evacuation of over 5000 people.

 

Spanish police officers evacuating people from the course of a lava flow on La Palma. Emilio Morenatti/AP.

The eruptions continued through the remainder of September, producing ash columns that rose up to 5 km above sealevel and lava flows that reached the west coast of the island at Playa de los Guirres, destroying over 650 buildings and 18.9 km of roads, and sulphur dioxide emissions of up to 25 000 tons per day. 

 

Lava engulphing a residential building on La Palma. AP.

On Friday 1 October 2021 a third vent was discovered to have opened on the side of the volcano, producing two new lava flows, one of which flowed rapidly towards the town of Los Llanos de Aridane, which has been partly evacuated in response. A total of over 6000 people have now been evacuated from their homes on the island, with over 7 km² covered by lava flows and over a thousand homes and other buildings destroyed.

 

Satellite image of a lava flow running through a settlement on the west coast of La Palma. Copernicus Sentinel/European Space Agency/Reuters.

The Canary Islands are a group of volcanic islands fuelled by a mantle plume rising through the African Plate, on which they are situated. The plume is rising from deep within the Earth, and is independent of the movement of the tectonic plates at the Earth's surface. As the plate moves relative to the hotspot new volcanic islands form on its surface, each over the hotspot when it forms, with the oldest islands of the chain in the east (the African Plate is being pushed east by the expansion of the Atlantic Ocean, but the hotspot is relatively motionless).

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Flights to and from the Canary Islands cancelled due to dust storm.

Flights to and from the Canary Islands have been cancelled today due to a major dust storm brought clouds of red sand from the Sahara to the islands, greatly reducing visibility. Several local events have also been cancelled due to the storm, and people with respiratory problems are being warned not to go outside until the storm has passed. The dust storm has been caused by winds of up to 120 km per hour over parts of North Africa, and is expected to pass on Monday 24 February 2020.

A dust storm in Santa Cruz de Tenerife on Sunday 23 February 2020. Andres Gutierrez/AP.

The predominant weather system over North Africa is the Saharan Air Layer, a hot, dry, and often dust-laden air system that prevents moister air from the Atlantic and Mediterranean brining rain to the area. Over the Atlantic this layer is typically forced up, above the moist, but cooler, sea air, carrying dust westward to South America. However, on some occassions a climatic inversion, whereby the air from the Saharan Air Layer is unable to move westward, and piles up in position till its upper layers become cool and dense enough to be forced down, brining a dense, dust-laden storm to the Canaries, known as a Calima.

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Thousands forces to flee their homes as wildfire sweeps across central Gran Canaria.

Around 9000 people have been forced to flee their homes as a wildfire sweeps across the northwest part of central Gran Canaria this week. The fire started near the town of Tejeda on Saturday 17 July 2019, and has so far proved impossible to bring under control. The fire has destroyed about sixty square kilometres of land cover in a mountainous region largely covered by wooded ravines, much of it in the ancient Pine forests of the Tamadaba Natural Park. There are no reports of any injuries at this time, but it is thought that several hundred homes have been destroyed.

Fire burning near El Rincón on Gran Canaria on 18 August 2019. Cabildo de Gran Canaria/AP.

The cause of the fire has not yet been determined, though local authorities have not yet ruled out the possibility that it may have been deliberately set, but it has spread rapidly due to a combination of exceptionally high temperatures in the area (over 40°C), combined with low humidity and high winds. Flames in excess of 50 m high have been reported, which helps the fire jump to new places. Pine forests are particularly prone to fires, as Pines produce a large number of long, flammable needles, which drop to the ground around the trees, causing any fires to burn rapidly and intensely.

Fire fighters trying to tackle a wildfire on Gran Canaria this week. AP.

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Bryozoas from the seamounts, islands, and continental slopes of the northeast Atlantic.

Bryozoans, or Moss Animals, are colonial filter-feeding invertebrates that form encrusting or weed-like colonies. The individual 'animals' are on average about 0.5 mm in length, and live inside a protective covering from which they extend a crown of cilia-covered tentacles called a lophophore. These are not true individuals though as they develop as buds on the colony and share nutrients; for this reason they are referred to as 'zooids'. The colonies produce sexually by means of reproductive zooids that have gonads, but lack feeding apparatus. Bryozoans are widespread globally, but are often overlooked because they are small and the colonies resemble plants.

In a paper published in the European Journal of Taxonomy on 31 August 2017, Björn Berling of the Oberösterreichisches Landesmuseum, and the Centro de Investigação em Biodiversidade e Recursos Genéticos, Jean-Georges Harmelin of the Mediterranean Institute of Oceanography at Aix-Marseille University, and Beate Bader of the Institut für Geowissenschaften at Christian-Albrechts-Universität, describe ten new species of Bryozoas from the seamounts, islands, and continental slopes of the northeast Atlantic.

The first new species described is named Atlantisina atlantis, in reference to the Atlantis Seamount, where it was found; it is considered to be sufficiently different from a previoulsy described Bryazoans to merit also being placed in a new family, the Atlantisinidae. This an encrusting Bryozoan, forming ribbon-like colonies by linear budding. It has a translucent frontal shield covered with densely packed irregular nodules, and six spines around its oral orifice. The species was found encrusting Coral skeletons at depths of between 275 and 460 m.

 Atlantisina atlantis, Atlantis Seamount. Overview of colony growing on a Stylasterid skeleton; note the biserial-branching growth. Scale bar is 1 mm. Berling et al. (2017).

The second new species described is also placed in the genus Atlantisina and given the specific name meteor, in reference to the Great Meteor Bank, where it was discovered. This species is similar to Atlantisina atlantis, but has a frontal shield covered in nodules with flattened tips and eight spines around its oral opening. This species was found encrusting shells, pebbles and fragments of Coral skeleton on the Grand Meteor Bank and the Irving and Hyères seamounts at depths of between 270 and 750 m.

Atlantisina meteor, Great Meteor Bank, several autozooids and ovicellate zooids. Scale bar is 300 μm. Berling et al. (2017).

The third new species described is again placed in the genus Atlantisina, and given the specific name inarmata, meaning 'unarmed' as it lacks a spike beneath its mouth opening, someting found in many species. The frontal shield of this species is porcelain white, and covered with flattened nodules, and it has six spines around its oral opening. This species was found growing on shells, pebbles and fragments of Coral skeleton around Gran Canaria in the Canary Islands, at depths between 345 and 485 m.

Atlantisina inarmata, Canary Islands. An autozooid with a borehole in the frontal shield (centre), presumably drilled by a predatory Microgastropod, and one with an intramural bud (at right), indicated by the presence of a secondary orifice rim. Scale bar is 100 μm. Scale bar is 300 μm. Berling et al. (2017).

The forth new species described is again placed in the genus Atlantisina and given the specific name seinensis, meaning 'from Seine', in reference to the Seine Seamount, where it was discovered. This species has a frontal shield with large flattened nodules, six oral spines and a plate with a large spike beneath the oral structure. The species was found encrusting rocks at a depth of 235–260 m.

Atlantisina seinensis, Seine Seamount. Lateral view showing the vertical dimensions of the suboral umbones. Scale bar is 200 μm. Berling et al. (2017).

The fifth new species described is again placed in the genus Atlantisina and given the specific name tricornis, in reference to the sub-oral plate, which has a triple spike. The frontal shield of this species has a pattern of raised ridges around polygonal depressions, and it has six oral spines. The species was found encrusting rocks, Brachiopods, and fragments of Coral and other skeletal elements at depths of between 450 and 1040 m on the Iberian continental slope and between 675 and 1700 m on Galicia Bank.

Atlantisina tricornis. Colony from Galicia Bank forming biserial ribbons; note the relatively broad ooecia. Scale bar is 300 μm. Berling et al. (2017).

The sixth new species described is once again placed in the genus Atlantisina and given the specific name lionensis, meaning 'from Lion' in reference to Lion Seamount, where it was discovered. The frontal shield of this species has a pattern of raised ridges around polygonal depressions, it has six oral spines, and a suboral plate with three-to-five irregularly shaped spikes. This species was found encrusting small rocks at depths of between 320 and 630 m, on the Lion and Seine seamounts.

Atlantisina lionensis, Lion Seamount. Ovicellate zooids at the colony growth margin. Scale bar is 100 μm. Berling et al. (2017).

The seventh new species described is once again placed in the genus Atlantisina and given the specific name gorringensis, meaning 'Gorringe' in reference to the Gorringe Bank, where it was discovered. This species has a small, frontal shield with a reticulate pattern of raised ridges encircling round to polygonal depressions, six oral spines and a suboral plate with up to eight spikes. This species was found encrusting small shells and pebbles at depths of 180 to 330 m, on Gorringe Bank and Ampère Seamount.

Atlantisina gorringensis, Gorringe Bank. Periancestrular region, the constricted oral region of the partly overgrown ancestrula is to the left. Scale bar is 300 μm. Berling et al. (2017).

The eighth new species is once again placed in the genus Atlantisina and given the specific name acantha, meaning 'thorny', in reference to its suboral plate, which is flared and has a variable number of large spikes. The species has a frontal shield with a reticulate pattern of raised ridges encircling round to polygonal depressions and six oral spines. It was found growing on small rocks at a depth of 660 m off the coast of Gran Canaria.

Atlantisina acantha, Canary Islands. Close-up of ooecium and the suboral crest. Scale bar is 100 μm. Berling et al. (2017).

The ninth new species described is named Bathycyclopora suroiti, where 'Bathycyclopora' is a combination of 'bathyal', meaning 'deep' and 'Hemicyclopora', a previously described genus which it superficially resembles, and 'suroiti' in honour of French research vessel ‘Le Suroît’. This species has a frontal shield with pronounced ridges and seven or eight oral spines. It is an encrusting Bryozoan, with colonies forming patches with the individual zooids separated by grooves. This species was found on Atlantis Seamont at depths of 275–460 m, encrusting fragments of shell and Coral.

Baythycyclopora suroiti, Atlantis Seamount. Overview of a partly damaged colony. Scale bar is 100 μm. Berling et al. (2017).

The final new species described is named Calvetopora otapostasis, where 'Calvetopora' in honour of the early twentieth century marine biologist Louis Calvet, for his work on Bryozoans, and 'otapostasis', meaning 'protuding ears', in reference to the two avicularia (modified zooids that are used as suplimentary mouthparts) on either side of the oral opening. This species has a frontal shield with a granular texture and six oral spines. It forms large, patch-shaped colonies, which sometimes overgrow themselves, and was found growing on fragments of coral skeleton at depths of 280 to 460 m on Atlantis Seamount.

Calvetopora otapostasis, Atlantis Seamount. Slightly oblique view of an autozooid at the growth margin showing the communication pores in the lateral walls as well as marginal areolar pores (black arrow) and the roughly crescentically arranged pseudopores (white arrows) in the frontal shield. Scale bar is 200 μm. Berling et al. (2017).

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Series of Earthquakes beneath the Canary Islands.

The  Instituto Geográfico Nacional has recorded a series of deep tremor beneath the Canary Islands since Saturday 7 October 2017, with the majority of the tremors beneath the southern part of the island of La Palma. None of these events was large enough to cause any problems in itself, however the islands are volcanic in origin and seismic activity beneath volcanoes can be significant, as they are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode.

Earthquakes in the Canary Islands since 7 October 2017. Instituto Geográfico Nacional. 

The Canary Islands are a group of volcanic islands fuelled by a mantle plume rising through the African Plate, on which they are situated. The plume is rising from deep within the Earth, and is independent of the movement of the tectonic plates at the Earth's surface. As the plate moves relative to the hotspot new volcanic islands form on its surface, each over the hotspot when it forms, with the oldest islands of the chain in the east (the African Plate is being pushed east by the expansion of the Atlantic Ocean, but the hotspot is relatively motionless).

  

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Predicting eruptions in monogenetic volcanic fields.

Seismic activity and fumerol (gas) emissions are well established as predictors of eruptions on stratovolcanoes (volcanic mountains which undergo repeated eruptions), but predicting eruptions in other kinds of volcanoes is more problematic. Monogenetic fields are areas of volcanic activity where sporadic eruptions occur at different locations, rather than at a single site. Most such sites only suffer very irregular eruptions, but the fields are often home to hot spring systems or other features which make them attractive to humans, leading to settlement in potentially hazardous areas, making finding a method for predicting eruptions in these areas a priority.

In a paper publishd in the journal Geology on 5 February 2016, Helena Albert of the Central Geophysical Observatory at the Spanish Geographic Institute, Fidel Costa of the Earth Observatory of Singapore and Asian School of the Environment at the Nanyang Technological University and Joan Martí of the Institute of Earth Sciences Jaume Almera, discuss a number of historic eruptions at a number of different monogentic fields, with a view to understanding the processes driving volcanic activity at these sites and the possibility of predicting future eruptions in such areas.

Albert et al. examined ten historic eruptions at five mongenetic fields; the 1704-05 Tenerife eruption (part of the Canary Islands Volcanic Field), the 1909 Tenerife eruption, the 1949 La Palma eruption (also in the Canaries), the 1971 La Palma eruption, the 2011 El Hierro eruption (again in the Canaries), the 1759 Michoacan eruption (in the Michoacan-Guanajuato region of Mexico), the 1943 Michoacan eruption, the 1943 Goropu Mountains eruption (part of the Owen Stanley Range of Papua New Guinea), the 1973 Heimaey Island eruption (Iceland) and the 1989 Higashi-Izu eruption (on the Izu Peninsula, Japan).

 Emissions from the 2011 El Hierro eruption, which happened offshore to the south of the island. Guardia Civil.

Of these, only the 2011 El Hierro eruption was monitored with high quality modern seismic equipment, with three others having lower quality records available. However witness accounts of earthquakes provide insight into seismic activity in all of these fields prior to the onset of eruptive activity. All of the eruptions were proceded by periods of seismic activity, with the longest such recorded period preceding the 2011 El Hierro eruption, where tremmors were recorded 4-5 years ahead of the eruption, and the shortest being the 1973 Heimay Island eruption, where seismic activity was only noticed 2 days before the main eruption.

Lava flow from the 1973 Heimay Island eruption which entered the town of Vestmannaeyjar, destroying about half of the homes there and causing the population to evacuate to the Icelandic mainland. Will Perry/The Reykjavík Museum of Photography.

Albert et al. next looked at samples of erupted lava from all of the eruptions except the 1943 Goropu Mountains eruption and the 1989 Higashi-Izu eruption. In each case they found that the lavas were mineralogically mixed, that is to say included minerals thought to come from different magmatic intrusions. Magma extruded from deep within the Earth is thought to be more-or-less entirely liquid, however if it becomes trapped in chambers close to the surface (5-15 km underground) it cools foming a mush with crystals suspended in a liquid matrix. Different minerals are formed at different temperatures, and larger crystals form more slowly (implying the mush has remained cool enough for the crystals to form but hot enough for the matrix to remain liquid for a longer period of time), giving each magmatic intrusion its own distinctive makeup. Lavas with mixed compostitions contain crystals which cannot have formed in a single intrusion.

Ruins of the San Juan Parangaricutiro Church which was destroyed by the 1943 Michoacan eruption. Sparks Mexico/Wikipedia.

From this Albert et al. conclude that each of these volcanoc fields is fed by a an extensive shallow plumbing system with an extensive system of dykes at mid-crustal levels recieving intermittent intrusions of deep magma. While a full understanding of the processes behind this is beyond the scope of this study, the majority of these eruptions were preceded by a rise in seismic activity which began months to years before the main eruptive episodes, giving the potential for the prediction of such eruptions using dedicated seismic monitoring networks.

 Possible plumbing system configuration and evolution of events that may occur below monogenetic volcanoes (schematic and not to scale). The depth of the subvolcanic system may vary from 5 to 15 km. The depth of the magma source is also variable but is at least 20 km. (A) Intrusion of magma approximately one or two years prior to the eruption, stalling of magma at 5–15 km due to the loss of buoyancy or freezing of dikes, and mixing processes registered by the crystals. Crustal assimilation occurs in some cases. Seismic activity is felt by the population in some cases. (B) Renewal of magma intrusion, progressive opening of the path between deep and shallow reservoirs, and mixing processes registered by the crystals. Crustal assimilation occurs in some cases. The seismic activity is commonly felt by the population. (C) Continued intrusion of mafic magma leads to easier transfer from deep to shallow reservoirs, and this allows the magma to finally erupt. Magma mixing (and crustal assimilation in some cases) are recorded by the crystals. Seismicity is felt by the population. Also shown the possibility that magma is directly transfer from the mantle to the surface. Albert et al. (2015).

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Magnitude 5.4 Earthquake off the coast of El Hierro.                                                          The United States Geological Survey recorded a Magnitude 5.4 Earthquake at a depth of 22.8 km roughly 31 km to the northwest of the island of El Hierro in the Canaries, slightly after 5.45 pm local time (which is GMT) on Friday 27 December 2013. There are...

The floating stones of El Hierro.               When volcanic activity began off the south coast of El Hierro, in the Canary Islands, in October 2010, it led to the production of large plumes of pumice-like rocks that floated on the surface of the ocean, producing a distinctive volcanic 'stain'. Pumice is a volcanic rock which contains large vesicles (sealed, gas filled cavities) which cause it to float on the water, which is formed by superheated magma coming...

Earthquake of the coast of El Hierro.           On Friday 29 March 2013, slightly after 5.00 pm GMT, the United States Geological Survey recorded a Magnitude 4.6 Earthquake at a depth of 17.3 km, roughly 30 km southwest of El Hierro in the Canary Islands...

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