Month: May 2020

Going With The Flow

From the pen of the 19^th century French science fiction writer Jules Verne, ‘A Journey to the Centre of the Earth’ is the adventure novel which fuelled my boyhood interest in geology. The tale is very much connected to volcanism. The three protagonists begin their audacious expedition by descending through a volcanic vent on Snaefellsjokull in Iceland and later resurface by means of a similar conduit in sunnier climes on Stromboli, one of the Aeolian Islands in the Mediterranean. The scene, as the story draws towards its climactic finale, sees our travel-weary friends sitting on a wooden raft in something of a dangerous predicament. To quote:

‘An eruption’, I gasped. ‘We are, then, in the volcanic shaft of a crater in full action and vigour’

‘I have every reason to think so,’ said the Professor in a smiling tone, ‘and I beg to tell you that it is the most fortunate thing that could happen to us.’

Carried ever upward by the pressurised surge of bubbling lava, the raft is eventually popped out of the neck of the volcano like the cork in a champagne bottle. Remarkably the trio survive this explosive ordeal to relate the tale of their subterranean wanderings. It left an indelible impression and I have had a passionate interest in volcanic rocks ever since. Pure fantasy of course, but wonderful stuff, nonetheless. In reality, volcanic eruptions are something quite different.

**Volcanic dust, Eyjafjallajokull, Iceland 2010**

A highly explosive eruption began in the south of Iceland in April 2010. The volcano in question was Eyjafjallajokull. A vast quantity of volcanic dust was ejected, some of it up to a height of over 9.5 km into the atmosphere, forming a dramatic dark plume. Ferried by the wind across to Europe, the fine-grained tephra caused chaos in the following weeks as thousands of planes were grounded because of the danger it posed to their engines, leaving millions of passengers temporarily stranded. Large expanses of the Icelandic countryside were shrouded in a covering of ash including Heimaey in the Westmann Islands lying off the south-west coast. This is the youngest rock in my collection that only recently celebrated its 10^th birthday!

In January1973 a volcanic eruption began on Heimaey. Most of the islands’ inhabitants were evacuated to safety in the local fishing trawlers to mainland Iceland leaving volunteers behind to save what they could. When the eruption finally abated several months later the people returned to their island home. They found a third of the town encased in a thick deposit of cinder-like tephra. This has earned it the nickname of ‘Pompeii of the North’. Some of the houses have been ‘archaeologically’ excavated and now form the centre piece of a museum which details this volcanic event and its effects on the island community.

During an eruption blobs of lava are blown high up into the air and, as they spin, cool and solidify before landing on the ground. These are known as ‘volcanic bombs’ and many have a distinctive rugby football shape as in the specimen illustrated here. These ballistic missiles can be dangerous, as Pierce Brosnan’s partner Marianne discovered in the opening scene of the 1997 movie ‘Dante’s Peak’. Volcanic bombs rain down as the couple attempt to flee from their research base. It doesn’t end well for the girl! Well worth checking out on YouTube !

Lava immediately begins to cool on exposure to the air and this causes a crust to form on the surface which becomes wrinkled as it is stretched by hotter lava flowing underneath. This rock is called ropy lava.

Pumice is a rock formed when gas-rich lava cools. Because of its low density the rock can float. Known universally as ‘pumice stone’, it is used for removing dry, dead skin. It is common on Lipari in the Aeolian Islands where sizable fragments can be acquired. The specimen included here weighs just under 1.8 kg. The island also has deposits of obsidian, a volcanic glass formed when lava cools rapidly, fine specimens of which are readily available. Obsidian from this island was traded widely and used for fashioning tools and weapons in prehistoric times.

Best,

Vincent

Tags eyjafjallajokull, pompeiiofthenorth, volcanicbomb, volcano

Cabinet of Curiosities

Having A Blast

I have a large collection of vintage trade cards. These were produced in the main by cigarette companies as a marketing ploy, the intention behind which was to increase product sales. In sets of 25 & 50 individual cards, they showcased a wide range of disparate subjects from wildlife to cricket heroes and were a favourite with children enthused with collecting them. On the front of each was a high quality full-colour drawing, accompanied on its reverse side by a text, in Lilliputian print, which provided succinct facts pertaining to the subject in the illustration. In effect the cards were an important educational resource, helping to spread knowledge on a host of subjects including wildlife, archaeology, industry, sport, history and science to the wider general public. They became hugely popular. The pastime of collecting cards is called cartophily, deriving from a combination of the French ‘carte’ (card) and Greek ‘philos’ (loving). One who indulges in this engaging activity is known as a cartophilist.

The company Chivers, who make jellies and jams, brought out a series called ‘Wild Wisdom’ in the 1960’s. One of the cards featured the weird and wonderful Bombardier beetle. This small fellow has a most unusual defensive technique to discourage predators approaching it from behind. If threatened, the beetle discharges a liquid from its rear opening which on contact with the air bursts into flame, the reaction accompanied by an explosive sound. This highly effective mechanism earned it the name bombardier. The beetle does not occur in Ireland.

A series of cards brought out in 1922 by the cigarette company Wills was titled ‘Do You Know’ and featured a wonderful array of subjects, some of which related to natural history, including the limpet (Patella vulgata). This marine mollusc adheres to the surface of a rock with its powerful muscular foot. When the tide comes in it heads off to feed using the teeth on its radula to graze algae. Interestingly, the creature appears to be something of a home bird. As the tide begins to drop, each individual returns to the exact spot it left and settles into the grooves that the edges of the shell have cut over time into the rock surface, a molluscan personal parking place ! Some fine examples of these are visible on this fragment of limestone I picked up on a north Dublin beach in 1974.

A selection of different bird eggs is detailed on another card from the same series. Seabird eggs are collected annually on Grimsey Island as they become seasonally available. Straddling the Arctic Circle 25 miles off the northern coast of Iceland, it is home to large numbers of guillemots who lay their eggs on the bare rocky ledges of the coastal cliffs. Lowered by rope, the collectors work their way along these precarious footholds picking them up. This was a common practice at one time among some island communities here in Ireland. Childhood memories of collecting eggs on the Blasket Islands are included by Maurice O’Sullivan in his book ‘Twenty Years A-Growing’, first published in 1933. The tapered shape of the guillemot egg may help prevent it from rolling off the ledges. It spins in a tight circle if hit and so ultimately remains safely in place. On a visit to Grimsey a few years ago while working onboard the expedition cruise ship, National Geographic Explorer, we were presented with a large bucket of newly collected guillemot eggs. Ear-marked to be hard-boiled in the ship’s galley, I liberated a few specimens for teaching purposes. They come in a range of attractive colours and have a distinctive flecked pattern.

Guillemot eggs from Grimsey Island, Iceland

Included in a 1960’s Musgrave Tea Company set of cards, the pygmy shrew is Ireland’s smallest mammal and weighs a mere 5 grams. It only lives for a year, so needs to pack in quite a lot in a short time frame. Highly energetic, the animal is a ferocious hunter and dines on small insects and grubs. They have tiny, bead-like eyes, which may account for its Irish name, dallóg fhraoigh, meaning ‘blind animal of the heather’. I once came across a mummified shrew in a bottle and managed to extract it from its glass-walled death-trap. It has since resided in the cosy confines of a match box.

Best,

Vincent

Tags birdseggs, bombardierbeetle, grimseyisland, guillemot, limpet, nationalgeographicexplorer, shellfish, shrew

Cabinet of Curiosities

Shelling Out

The bivalve Great Scallop (Pecten maximus)

The great scallop (Pecten maximus) is a bivalve, a marine mollusc possessing two shells. The 18^th century Swedish scientist Carl Linnaeus is regarded as the father of taxonomy, the academic discipline whose focus is the classification and naming of organisms. His binomial system consists of two parts, the first or generic name which describes the genus or family to which a living organism belongs, coupled with a second, specific one. Scientific names are an engaging study in themselves. Pecten derives from the Latin ‘pectere’ meaning a ‘comb’ and relates to the similarity in shape to a stylish form of that implement, while ‘maximus’ means ‘largest’. It is commonplace to see the convex lower shell used as ashtrays and is familiar worldwide as the logo of the Shell Oil Company.

Pilgrim keepsake – the lower, convex valve

The shell is also a symbol very much associated with St. James the Apostle and his final resting place at Santiago De Compostella in Galicia, Spain. One of the most venerated religious sites in the world, pilgrims have flocked there since Medieval times. Returning devotees wore a scallop fixed to their hats or clothing to indicate that they had visited the site and it remained a cherished keepsake. An efficient vessel for scooping up water to drink, its radiating ribs symbolised the numerous pilgrim routes crossing Europe and converging at Santiago De Compostella. In 1996 the site of an Augustinian monastery and burial ground in the town of Mullingar was excavated by archaeologists. Burials were unearthed dating to the 14^th century, some of which contained scallop shells indicating that their owners had made the arduous journey. A bronze statue was commissioned by the town to commemorate the Millennium in 2000. Called ‘The Pilgrims’, it features two Augustinian monks one of whom wears a scallop and links the modern town to its Medieval origins.

The ‘scallops’ served in seafood restaurants are the bivalves’ adductor muscle, by the alternate contracting and relaxing of which the shells are opened and closed. This action squeezes out water around the hinge at the back, the force of which propels the bivalve forward.

A neat circular perforation is noticeable near the centre of the fossil pecten shell. This is known as a predatory borehole and was drilled by some ancient form of whelk around 50 million years ago in the Eocene Epoch. Once the prey had been located, it drilled through the victims’ shell using its tooth-lined radula. As soon as the hole had been completed, the whelk secreted an enzyme into the scallop which immediately began to digest the flesh which it then consumed. A stony, still-life study of life and death in our distant past.

Echinoderms are a group of spiny skinned marine animals which display a five-fold radial symmetry. They include starfish, sea urchins, sea-lilies and brittle-stars. The skeletons of these animals are composed of the mineral calcite and as a result their ancient ancestors are commonly preserved as fossils. The sea-lilies are also known as crinoids, from the Greek ‘krinon’ and ‘eidos’ meaning ‘lily’ and ‘form’ respectively and stems, no pun intended, from their superficial resemblance to flowers. An extensive family, over 6,000 fossil species have so far been identified.

Fixed on the end of a long stalk by which it was attached to the seabed, the body had arms equipped with fine feathery filaments that directed tiny food particles towards the mouth. The crinoids consisted of numerous conjoined disc-shaped segments which formed the hard structure of the animal. A small number of related species are still found in the depths of the world’s oceans. Working on an expedition to the Sahara Desert in Morocco some years ago I came across some fine crinoid fossils of a species called Pentacrinites. They are around 400 million years old and clearly display the feathery filaments on the arms.

Best,

Vincent

Tags crinoidfossils, echinoderm, fossilmolluscs, greatscallop, Santiagodecompostella