Sunday 31 December 2023

Cycadodendron galtieri: Cycad wood from the Permian of Saxony, central-eastern Germany.

Cycads are a thought to have been among the earliest Gymnosperm Plants to have appeared, with molecular clock estimates suggesting that they diverged from other Gymnosperms in the Late Carboniferous or Early Permian. The group underwent a major evolutionary radiation in the Early Triassic, and fossils are abundant in Mesozoic and Cainozoic deposits. These fossils tend to closely resemble modern Cycads, despite these sharing a fairly recent common ancestor, suggesting a high degree of morphological conservatism within the group. Palaeozoic fossils are much less common, and can be more difficult to interpret. These comprise possible Cycad megasporophylls (leaves) from the Late Carboniferous and Early Permian, although it is difficult to be confident about the affinities of these.

In a paper published in the International Journal of Plant Sciences on 11 October 2023, Ludwig Luthardt of the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Research, Ronny Rößler of the Museum für Naturkunde Chemnitz and the Department of Palaeontology at the Technische Universität Bergakademie Freiberg, and Dennis Stevenson of the New York Botanical Garden and the School of Integrative Plant Science at Cornell University, describe a new species of Cycad based upon a piece of stem wood from the Holocene gravel deposits of the Zwickauer Mulde river, which are known to produce silicified woods derived from the Permian Chemnitz Fossil Lagerstätte.

Geography and geology of the source area of the fossil Cycad stem, combining the catchment area of the Zwickauer Mulde River/Chemnitz River with the most important localities of mainly in situ found petrified wood and their stratigraphic affiliation. Abbreviations: NSVC, North SaxonyVolcanite Complex; ZVC, Zeisigwald Volcanic Complex. Luthardt et al. (2023).

The new species is named Cycadodendron galtieri, where 'Cycadodendron' means 'Cycad-tree' (the suffix '-dendron' is commonly used for fossil woods, on the basis that chunks of wood of any size must have come from a tree), and 'galtieri' honours Jean Galtier, a renowned palaeobotanist from Montpellier, France, for his significant contributions to the knowledge of the evolution and anatomy of Palaeozoic fossil Plants. It is described from a single piece of polished wood, K9883, roughly 69 mm by 56 mm, thought to have derived from a larger stem, as the outer parts, including the cortex and vestiges of leaf bases, are not preserved.

Overview of polished sections of Cycadodendron galtieri (K9883, holotype). (A) General view of the specimen in transverse section. K9883a. (B) Counterpart of the specimen, additionally cut in radial sections. K9883b, K9883c. (C), (D), Radial sections of the specimen; successivevascular cylinders are indicated by arrows and X1–X9 in (D). K9883b, K9883c. All specimens are at the same scale. Luthardt et al. (2023).

While foliage can be difficult to ascribe to a particular plant group, due to convergent evolution among plants living in similar environments, the wood of Cycads is highly distinctive, with vascular stands arranged in medullary bundles within a wide inner pith, surrounded by consecutive vascular segments each producing centripetal secondary xylem and centrifugal phloem. The presence of these features within Cycadodendron galtieri marks the specimen as an unequivocable Cycad, and therefore the oldest known fossil which can be confidently assigned to the group.

Anatomical sketches of Cycadodendron galtieri with the overall arrangement of stem tissues. (A) Transverse section showing the pith with medullary bundles and pith-peripheral bundles, successive vascular segments, and traversing medullary bundles. K9883a. (B) Radial section exhibiting vertical arrangement of stem tissues and indicating the number of successive vascular segments and phloem-parenchyma zones. K9883b. Luthardt et al. (2023).

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The Earth approaches perihelion.

On Wednesday 3 January 2024 at 0.3f8 am, GMT, the Earth will reach its perihelion; the closest point on its orbit to the Sun, when it will be 147 069 667 km from the Sun. This is because the Earth's orbit is not a perfect circle, but varies by 3.3% over the course of a year. The Earth will reach its furthest point from the Sun, at a distance of 152 141 035 km, at 5.06 am GMT on 5 July 2022. This perihelion distance varies each year; in 2023 the Earth reached 147 098 928 km from the Sun and in 2025 it will reach 147 099 586 km. 

The Earth's Aphelion and Perihelion. My Dark Sky.

This means that the Earth is at its closest to the Sun in the middle of the Northern Hemisphere's winter, counter-intuitive to most of the planet's population. This is, however, purely coincidental; the Earth's seasons are not caused by its distance from the Sun, which only varies by 3.3%, but rather by the tilt of the planet. The Earth is currently tilted at an angle of 25.5° to its plane of orbit (this varies on a timescale of tens of thousands of years, but remains fixed from the point of view of any human observer), causing the Sun to appear to rise higher and lower in the skies of each hemisphere as the year goes by. In the northern winter the Southern Hemisphere is tilted towards the Sun, so that the days are longer there (and in around the Southern Solstice in December, permanently above the horizon at the South Pole). In addition, the Sun being directly overhead means that the energy from the Sun has to pass through less of the atmosphere before it reaches the surface of the Earth, so that less energy is lost to the atmosphere, causing the surface to warm.

How the tilt of the Earth relative to its plane of orbit causes the seasons. ESA.

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Saturday 30 December 2023

Trimeresurus ayeyarwadyensis: A new species of Mangrove Pit Viper from the Ayeyarwady and Yangon regions in Myanmar.

The taxonomy of the Asian Pit Viper genus Trimeresurus have proved difficult to unravel, as species tend to be both similar to one-another and morphologically variable. The Mangrove Pit Vipers, Trimeresurus purpureomaculatus and Trimeresurus erythrurus are considered to form a species complex, with Trimeresurus purpureomaculatus being an obligate Mangrove-inhabitant with variable colouration and dark blotches on its back, found in southern Thailand, Peninsula Malaysia, and on the island of Sumatra, while Trimeresurus erythrurus is a green Snake lacking markings, found in but not restricted to Mangroves, found in northern Myanmar, and eastern Bangladesh and India. Between these, in southern Myanmar, is a population of Snakes which show a mixture of traits seen in the other two groups, which have been assumed to represent a zone of hybridization. However, a recent study of genetic structures within the group has suggested that this southern Myanmar population is actually a separate species, which forms a sister taxon to Trimeresurus purpureomaculatus, although this species does show signs of hybridizing with Trimeresurus erythrurus.

In a paper published in the journal ZooKeys on 13 December 2023, Kin Onn Chan of the Lee Kong Chian Natural History Museum at the National University of Singapore, and the School of Biological Sciences at the Universiti Sains MalaysiaShahrul Anuar, also of the School of Biological Sciences at the Universiti Sains Malaysia, Ananthanarayanan Sankar of the Herpetological Society of Singapore, and the Department of Biological Sciences at the National University of Singapore, Ingg Thong Law and Ing Sind Law, also of the Herpetological Society of Singapore, Rasu Shivaram, also of the Lee Kong Chian Natural History Museum at the National University of Singapore, and of the Herpetological Society of Singapore, Ching Christian, again of the Herpetological Society of Singapore, and of the Department of Life Sciences at the Natural History MuseumDaniel Mulcahy of the Museum für Naturkunde at the Leibniz Institute for Evolution and Biodiversity Science, and Anita Malhotra of the School of Natural Sciences at Bangor University, formally describe the southern Myanmar Trimeresurus population as a new species. 

The new species is named Trimeresurus ayeyarwadyensis, meaning 'from Ayeyarwady'; the species is known from the Ayeyarwady and Yangon regions on the Ayeyarwady delta in southern Myanmar. The species has partially fused first infralabial and nasal scales, a condition not seen in any other member of the genus Trimeresurus, but otherwise shows a mosaic of traits seen in other species.

An unvouchered, live specimen of Trimeresurus ayeyarwadyensis from the Yangon Region, Myanmar. Wolfgang Wüster in Chan et al. (2023).

Unhybridized populations of Trimeresurus ayeyarwadyensis were found in Mangrove forests in the Pyapon and Myaungmya districts of the Ayeyarwady Region, as well as in a forest surrounding a lake unconnected to any Mangrove system in the Hlawga Park in the Yangon Region. In the Pathein District of the Ayeyarwady Region a population of Trimeresurus ayeyarwadyensis hybridized with Trimeresurus erythrurus was found living alongside an unhybridized population of Trimeresurus erythrurusTrimeresurus purpureomaculatus is known from the Dawei District in the Tanintharyi Region of Myanmar, and could potentially have a contact zone with Trimeresurus ayeyarwadyensis in Mon State, where no members of the genus Trimeresurus have been recorded, but this is thought likely to be due to a lack of searching rather than an absence of Snakes.

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Friday 22 December 2023

Examining the possibility of undetected small terrestrial planets in the Outer Solar System.

Free floating planets (which is to say, planet-sized objects floating free in space, unbound to any star) were first observed more than two decades ago, and this population is now known to contain terrestrial mass objects as well as large Jupiter-type planets.

In a paper published in The Astrophysical Journal Letters on 18 December 2023, Amir Siraj of the Department of Astrophysical Sciences at Princeton University, discusses the possibility that one or more terrestrial sized planets might have been captured by the Sun's gravity early in the history of the Solar System, and be as yet undiscovered components of the Outer Solar System.

Siraj notes that this is a different topic to the search for Planet Nine, a hypothetical body with a mass six times that of Earth and a semi major axis (average distance from the Sun) of about 400 AU (i.e. 400 times as far from the Sun as the Earth), which has been proposed due to observed clustering extreme trans-Neptunian objects in the Outer Solar System.

Siraj instead debates the possibility of sub-Earth-mass planets in the Outer Solar System, motivated by the fact that such bodies have been observed free floating in space, and could potentially be captured by the Sun's gravity.

An artist's impression of a free floating planet. NASA/JPL/CalTech/Wikimedia Commons.

In theory, any stellar system is most likely to capture drifting planets when it is still very young, and within its birth cluster, that is to say a cluster of stars forming within a single molecular cloud, which acts as a stellar nursery. This is the stage at which young stellar systems are most likely to eject planets, and the time when they are close to the largest number of other systems, making it most likely that such planets will be captured.

Stellar nurseries are variable in nature, with planets more likely to be captured in clusters where the molecular cloud is expanding rapidly. To give a conservative estimate of the probability of planet-capture, Siraj assumed a gently collapsing cluster, which is thought to be the environment in which planetary capture is least likely.

Surprisingly, despite applying the most conservative conditions, Suraj's simulation predicts that there wit be approximately 1.2 captured planets with a mass at least equivalent to that of Mars in the Outer Solar System, and 2.4 planets with a mass equivalent to Mercury or larger. If less conservative assumptions are made, this increases to roughly 2.7 planets with a mass equal to that of Mars or larger, and about 5.2 Mercury sized or larger planets. The average distance from the Sun of these planets would be 1400 AU, with half of all such bodies orbiting at between 600 AU and 3500 AU.

Detecting such planets would be another problem, as they would be very faint objects, and we do not actually know where to look for them. The Legacy Survey of Space and Time project at the Vera C. Rubin Observatory is due to Survey the entire Southern Hemisphere sky every three nights in six optical bands ranging from 320 to 1050 nm for a ten year period. 

The largest high-performance optical lens ever fabricated (1.55 m feet in diameter) in a clean room at the SLAC National Accelerator Laboratory, where the lab assembles the 3,200-megapixel digital camera of the Legacy Survey of Space and Time instrument. Farrin Abbott/SLAC.

This survey should be capable of detecting such planets in the Outer Solar System, if they are present and visible from the Southern Hemisphere (bodies in the Outer Solar System will orbit extremely slowly, taking hundreds or even thousands of years to complete a single orbit of the Sun, and are also likely to have more eccentric orbits than the planets of the Inner Solar System, making it possible that bodies could spend an entire ten year period in the northern sky). Suraj estimates that this survey could detect between about 1.0 and 1.4 Mercury sized planets, and 0.7-0.9 Mars sized planets, although only planets in the innermost part of the Outer Solar System, between about 400 AU and about 700 AU from the Sun. 

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Thursday 21 December 2023

Identifying the skins used to make Scythian leather.

The term 'Scythian' has been used to describe a vast array of nomadic people's living on the Eurasian steppes in the first millennium BC, who played an important role linking the sedentary civilizations of Europe to those of Asia. The term was originally used by Greek writers such as Herodotus to describe the peoples of the Pontic Steppes to the north of the Black Sea, a group best known in the archaeological record for their spectacular elite burials and the highly decorative gold items found within them. The lives of ordinary Scythians, however, are less well understood, as the materials from which they made the majority of their clothing, tools, and weapons, such as wood, bone, leather, and textiles, tend not to preserve well, and often degrade into unphotogenic fragments.

In a paper published in the journal PLoS One on 13 December 2023, Luise Ørsted Brandt of the Globe Institute at the University of Copenhagen, Meaghan Mackie, again of the Globe Institute, and of the Novo Nordisk Foundation Center for Protein Research, also at the University of Copenhagen, Marina Daragan of the Institute of Archaeology of the National Academy of Sciences of UkraineMatthew Collins, also of the Globe Institute at the University of Copenhagen, and of the McDonald Institute for Archaeological Research at the University of Cambridge, and Margarita Gleba of the Dipartimento dei Beni Culturali at the Università degli Studi di Padova, present the results of a study of Scythian leather samples from southern Ukraine, which sought to identify the Animals whose skins were used to make the leather.

The leather examined came from 18 burials at 14 different sites in southern Ukraine. Many of the leathers were in an extremely fragmentary state, making it impossible to tell what sort of object they had come from. Some of these leathers may have come from leather clothing, particularly trousers, boots, or vessels of various types, although the majority are thought to have come two iconic Scythian leather objects, quivers, used to hold arrows, and gorytos, which were used to carry both arrows and bows. These items were clearly very important to the Scythians, and are found in almost all burials, as well as being depicted on numerous decorative items. The majority of quivers and gorytos are heavily decomposed when found, but can be identified by the presence of metal arrowheads. Quivers used by elite members of Scythian society were artistic and decorative objects, with the best-preserved examples, such as those from Bulhakovo and Ilyinka, give us some idea of how these items were constructed, but little us understood about the manufacture of the quivers used by ordinary members of Scythian society.

The sites from which leather samples were recovered: (1) Bulhakovo; (2) Ilyinka; (3) Kairy; (4) Kislychevate; (5) Ol’hyne; (6) Orikhove; (7) Otradne; (8) Sadove; (9) Tyahinka; (10) Vil’na Ukraina; (11) Vodoslavka; (12) Vysuns’k; (13) Zelene; (14) Zolota Balka. Marina Daragan in Brandt et al. (2023).

Traditional microscopy can sometimes be used to identify leathers, although this is difficult, as the scraping and tanning significantly alter the surface of the material significantly, and leathers from archaeological contexts tend to be further degraded by decay processes. Two samples within Brandt et al.'s study material were preserved with fur on, making it possible to use hair strands to identify the Animals from which the skin had come, but none of the other leathers could be identified by this technique. The first of the two fur samples came from what appears to have been a fur garment from Burial 1 within Kurgan 22 at the Vil’na Ukraina 3 cemetery (an adult woman, apparently of high status buried with jewellery, a mirror and mirror case, and domestic items in the second half of the third century BC), and was identified as having come from an unknown Mustelid, while the second came from a decorative quiver with fur fragments from Burial 3 (a child buried with weapons in the second or early third quarter of the fourth century BC) in Kurgan 4 at the Ilyinka cemetery, and was identified as coming from an unknown Rodent.

In order to identify the remaining leathers (and better identify the furs) Brandt et al. turned to biomolecular techniques. These have become increasingly important in archaeological investigations in recent decades, with DNA analysis allowing not just the identification of Animal and remains to species level, but quite often Human and Animal remains to specific populations, and the illumination of relationships between ancient and modern populations. DNA, however, is seldom recoverable from leather, as it is typically destroyed by the tanning process. Proteomics offers an alternative approach, enabling archaeologists to identify proteins (such as collagen in leather or keratin in hair) from small samples of material, including samples of material, which is likely to be to old, to degraded, or otherwise treated in ways which make the preservation of DNA unlikely.

A selection of the leather object fragments analysed: (1) Ilyinka Kurgan 4 Burial 2; (2) Ilyinka Kurgan 4 Burial 3; (3) Vodoslavka Kurgan 8 Burial 4; (4) Orikhove Kurgan 3 Burial 2; (5) Zelene I Kurgan 2 Burial 3; (6) Kairy V Kurgan 1 Burial 1; (7) Ol’hyne Kurgan 2 Burial 1; (8) Bulhakovo Kurgan 5 Burial 2; (9) Zolota Balka Kurgan 13 Burial 7. The units of the scale bars are cm. Marina Daragan in Brandt et al. (2023).

Forty five samples of leather from the eighteen burials were included in the study. Of these, thirty three samples were identified, sixteen to species level, four to a probable species, seven to family level, one to probable family level, and five to one of two or more species. The majority of the leathers come from domestic Animals, with more than half coming from Sheep and Goats. One sample, from part of a quiver recovered from Burial 2 at Kurgan 3 at Orikove (two adult males buried with a variety of weapons in the first half of the fourth century BC) came from either a Goat or a Reindeer. Another sample, from one of three quiver found in Burial 2 at Kurgan 5 at Bulhakovo (a probable adult male, buried with weapons, jewellery, and domestic items in the second quarter of the fourth century BC), was identified as Cattle leather. Another three samples of leather were identified as either coming from a Bovid or a Cervid, although they were too poorly preserved for any more precise diagnosis.

One of the samples, from a fragment of a leather mirror case found with Burial 1 at Kurgan 6 at Vysuns’k, which comprised two skeletons buried with weapons, jewellery, a mirror, and a Greek kantharos cup, in the second quarter of the fourth century BC, was found to have come from a Red Fox. Another, from a decorative quiver found in Burial 2 of Kurgan 3 at Orikove, came from an unknown Carnivore, probably either a Tiger, Lion, Marten, Wolverine, Otter, or Hyena. 

The piece of fur from a quiver buried with a child, previously identified as an unknown Rodent, was more precisely identified as having come from a Squirrel, although the exact species could not be determined. The fur garment buried with a high status woman, previously thought to be from an unidentified Mustelid, was re-classified as having come from an unknown Felid.

Finally, two samples of leather appear to have been made from Human skin. The first of these comes from one of the three quivers buried with a probable adult male from Kurgan 5 at Bulhakovo, and was identified as definitely Human. The second from Burial 2 of Kurgan 5 at Bulhakovo, in which two skeletons, interpreted as a man and a woman, were buried together in the second quarter of the fourth century BC, with a variety of goods including weapons, domestic items, and jewellery. This fragment was identified as coming from a member of the Family Homininae, which includes Chimpanzees, Bonobos, and Gorillas, as well as Humans, though it is unlikely that any of the other Hominin species were present on the Pontic Steppes in the fourth century BC, so this leather can also be assumed to be of Human origin.

There is no simple recipe for turning skin into leather; the skins of different Animals need to be treated in different ways to achieve a leather of acceptable quality. The fact that the Scythians were using leather derived from numerous different Animals implies that they had a sophisticated understanding of the leathermaking process, and were likely selecting leather from different Animals for different purposes, just as modern leatherworkers do.

The majority of the skins used for leather by the Scythians appear to have come from domestic Animals which would have been herded on the Steppes by the pastoralist Scythians, particularly Goats and Sheep, although at least one of the leathers in Brandt et al.'s study was derived from a Cow, and Horse leathers have been recovered from burials in the Tuva Region of Russia (although this is a long way from the Pontic Steppes). Such Animals are also frequently depicted in Scythian goldware, and bones of Goats and Sheep have been found within the Kurgans of Scythians, interpreted as the remains of funeral feasts.

Scythian gold pectoral from Tovsta Mohyla, Ukraine, depicting a number of domestic Animals. Brandt et al. (2023).

Several of the leathers, and in particular the furs, in Brandt et al.'s study derive from wild Animals, which appear likely to have been hunted for their skins, including a Red Fox, and unknown Cat, and a Squirrel. None of these have been previously identified in the Ukrainian Scythian archaeological record, but are consistent with the types of furs found in Scythian setting across the wider Eurasian area.

The discovery of Human skin being used to make leather by the Scythians is new, and significant. The Greek historian Herodotus, who wrote extensively on the Scythians, certainly described this practice, however Herodotus is known to have embellished his stories somewhat, leaving modern historians unclear as to what can be taken as fact and what is fiction. On this occasion, Brandt et al.'s work appears to confirm that Herodotus was telling the truth. 

Both the direct presence of leather in Scythian archaeological sites, and iconography produced by the Scythians themselves depicting garments, suggests that these people made extensive use of leather to make vessels, mirror cases, quivers, shoes, garments such as trousers and coats, and the lining for metal armour such as greaves. The Scythians are also known to have made extensive use of scale armour, in which metal scales were sewn onto a leather base. It is presumed that the Scythians made leather themselves, as described by Herodotus, although no direct evidence for this has been found on the Pontic Steppes (the such evidence has been found for the nomads of Kazakhstan and Eastern Tibet, whose life-styles are not thought to have been dissimilar to those of the Pontic Scythians). Notably, the Tovsta Mohyla pectoral appears to show two Scythian men engaged in either skinning a Sheep or production of a garment made of sheepskin.

Depictions of Scythian warriors wearing decorated sleeved leather garments: (1)–(2) Gilded silver bowl from Haimanova Mohyla, north chamber. (3)–(4) Golden cone from Perederiyiva Mohyla, Ukraine. Brandt et al. (2023).

However, many of the embossed decorations on quivers from southern Ukraine have a very Hellenic feel to them, suggesting that the Scythians of this region were obtaining materials by trade with the Pontic Greeks, and that some of the goods obtained in this way were either quivers, or materials used in the making of quivers. It is also possible that those Scythians in contact with Greeks adopted some of their decorative styles. Given that high status objects buried with members of the Scythian elite are often decorated with Greek mythological and decorative motifs, either seems plausible.

Some of the fragments of quivers had traces of a red pigment, which was found to be cinnabar, a naturally occurqring form of mercury sulphide. This pigment is known to have been used by the Scythians for a range of decorative purposes, making its presence on quivers a probable indicator of Scythian manufacture.

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Wednesday 20 December 2023

The December Solstice.

The December (or Southern) Solstice this year falls on Friday 22 December, with the Sun reaching its southernmost point in the sky at 3.24 am GMT. This is the shortest day of the year in the Northern Hemisphere, where it is known as the Winter Solstice and the longest day in the Southern Hemisphere, where it is known as the Summer Solstice. At very high latitudes the sun may not rise (Northern Hemisphere) or set (Southern Hemisphere) for several weeks on either side of the Southern Solstice.

The solstices are entirely a product of variation in the Earth's rotation on its axis, which is at an angle of 23.5° to the plain of the Earth's orbit about the Sun. This means that in December the Earth's Southern Pole is tilted towards the Sun, while the Northern Pole is tilted away from it. This means that around the Southern Solstice the Southern Hemisphere is receiving radiation from the Sun over a longer part of the than the Northern, and at a steeper angle (so that it to pass through less atmosphere to reach the planet), creating the southern summer and northern winter.

The tilt of the Earth during the December Solstice. Wikimedia Commons.

The solstices are fairly noticeable astronomical events, and tied to the seasons which govern the life cycles of life on Earth, and they have been celebrated under different names by cultures across the globe, but most notably by those at higher latitudes, who are more profoundly affected by the changes of the seasons.

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Volcanic eruption on the Reykjanes Peninsula, Iceland.

On 11 November 2023 residents of the town of Grindavík on the Reykjanes Peninsula, Iceland, were evacuated from their homes following a major increase in seismic activity beneath the nearby Fagradalsfjall Volcano. The evacuations were triggered by the discovery of a magma tunnel running directly beneath the town at a depth of about 1.5 km. This is about 12 km long, originating near Stóra-Skógfell hill, and running beneath the town and some way out to sea. Seismic activity in the area has remained high in the area in the intervening weeks, although some people had begun to return to their homes. 

Slightly after 10.15 pm on Monday 18 December 2023, a new volcanic fissure opened on the peninsula, spewing vast amounts of lava and prompting a new series of evacuations. The fissure is about 3.5 km in length, and about 3 km from the town of Grindavík. It is currently producing 100-200 m³ of lava per second, although this is not flowing towards the town, and is not thought to present a threat to Human life.

Lava spewing from a new volcanic fissure on the Reykjanes Peninsula, Iceland, which opened on Monday 18 December 2023. BBC.

Although dramatic, lava flows are not usually considered particularly dangerous, as their advancing fronts are quite slow and can quickly be outpaced by an able-bodied Human being. The more deadly volcanic events are pyroclastic flows, such as the one which engulphed the Roman town of Pompeii, in which clouds of superheated gas and ash move downhill at high speeds in an avalanche-like motion, and phreatic explosions, caused by bodies of lava encountering bodies of water, which evaporate almost instantly, causing huge explosions.

People watching a lava flow on the Reykjanes Peninsula, Iceland, this week. Kristin Elisabet Gunnarsdottir/AFP/Getty Images.

Iceland lies directly upon the Mid-Atlantic Ridge, a chain of (mostly) submerged volcanoes running the length of the Atlantic Ocean along which the ocean is splitting apart, with new material forming at the fringes of the North American and European Plates beneath the sea (or, in Iceland, above it). The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. The ridge itself takes the form of a chain of volcanic mountains running the length of the ocean, fed by the upwelling of magma beneath the diverging plates. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island. All of this results in considerable Earth-movement beneath Iceland, where Earthquakes are a frequent event.

The passage of the Mid-Atlantic Ridge beneath Iceland. NOAA National Geophysical Data Center.

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