Thursday 30 June 2011

The Cornish Tsunami

On Monday 27th June 2011 at about 10.30 am the south coast of Cornwall was hit by a small tsunami. This was a wave of about 20 cm when it hit Newlyn, but as it moved along the south coast it grew, reaching 30 cm at Plymouth and 40 cm by the time it had reached Portsmouth it had grown to 40 cm. In enclosed estuaries it grew further, reaching 70 cm in the Yealm Estuary (near Plymouth).

Tsunamis grow as they enter enclosed spaces such as estuaries or the English Channel (the growth of this particular tsunami from west to east occurred as it moved into the English Channel) since they are essentially pressure waves. Some event causes a rapid change in seawater pressure (typically an earthquake or a submarine landslide), which spreads out like ripples on a pond after a stone is dropped in (which is a small pressure wave). On open water this eventually dissipates, but if it reaches a coast then things get interesting. The sea narrows close to the shore (obviously) so when a wave of water hits it, it is forced up above the surface; the shallower the water, the higher the wave. Particularly large and powerful waves will continue over the land from the coast for some distance.

Of course waves do not just go up, they go down. So a tsunami isn't just a wave above the normal sea-level, it is typically preceded and followed by rapidly shallowing water. Thus people in areas prone to tsunamis know to evacuate the coast rapidly if the tide apparently goes out rapidly, since this is likely to be followed by the tide coming in rapidly. This gives us the English term 'tidal wave' which is no longer used, since it is inaccurate; the tides are caused by the gravity of the sun and moon, tsunamis are nothing to do with the tide. The term 'tsunami' comes from Japan, where earthquakes, and therefore tsunamis, are all to common.

The presence of a tsunami implies that an earthquake or landslip has happened. No earthquake was detected by seismometers in the UK; this is not greatly surprising as we don't have many. In the absence of any data, the most likely cause would be a landslip about 400 km of the coast of Land's End, where the continental shelf ends abruptly and there are steep marine cliffs. However landslips here usually cause small tsunamis on both coasts of Cornwall, not just the south. This leaves the possibility of an offshore earthquake somewhere to the south of Devon and Cornwall. This would be the third earthquake in the area within a month; a small earthquake struck 20 km east-south-east of Dartmouth, Devon, on the second of June and a small onshore earthquake hit the town of Newton Abbott, again in Devon, on the 23rd. These events could possibly be related; some sort of adjustment in the structure of the Earth beneath Devon and the western English Channel, possibly related to the expansion of the Atlantic, or the movement of Africa (pushing north into southern Europe) or Spain (rotating anti-clockwise).

See also The Newton Abbott Earthquake and Earthquakes on Sciency Thoughts Youtube.

Wednesday 29 June 2011

Head-butting in a Pachycephalosaur.

The pachycephalosaurs were a group of ornithischian (bird-hipped) dinosaurs most closely related to the horned and duck-billed dinosaurs. They were bipedal, herbivorous dinosaurs with distinctive thickened skulls. For many years palaeontologists have argued over wether these creatures fought by head-butting in a manor similar to modern goats or musk-ox; the thick skull looks immediately like an adaptation to this sort of combat, but some biologists have suggested that it had a porous structure unsuitable for this role and that it may have been a heat exchange mechanism, and that it may have been impossible for pachycephalosaurs to lower their heads in a way suitable for head-butting. Pachycephalosaurs ranged in size from under a meter to about four and a half meters in length, though the smaller forms lacked the thickened skulls and it has been argued that they may have been juveniles of the larger forms. They are best know from the Late Cretaceous, earlier forms have been found, but these are on the whole not good specimens, so the origins of the group are not well documented.

A reconstruction of two pachycephalosaurs fighting at Plzeň Dinopark in the Czech Republic.

This month (June 2011) a paper appeared in the Journal PLoS ONE by Eric Snively of the Department of Mechanical Engineering at Ohio University and Jessica M. Theodor of the Department of Biological Sciences at the University of Calgary in which they study the structure of the skull of the pachycephalosaur Stegoceras validum using a computerized tomographic scanner (CT scanner), and compare it to various modern mammals, then developed a computer model of how the skull would have dealt with the stress of impacts.

Stegoceras validum was a two meter pachycephalosaur from the Late Cretaceous (83-70 million years ago) of what is now North America. It has a good fossil record, with several known specimens and is the best studied of the pachycephalosaurs. Stegoceras had a 7.5 cm thick, rounded skull, which, it has been argued, would have been unsuitable for direct forehead-to-forehead butting as seen in goats or musk oxen, but more suited to side swiping as in giraffes or horses. Furthermore it has been suggested that Stegoceras could not have held its head down with its neck behind it as a goat does, but was obliged to hold its neck in an 'S' shape, as in a duck.

Snively and Theodor found that Stegoceras had a layered structure to its skull, with dense, rigid boney layers and spongey vascularized layers. They found similar structures in goats and musk oxen, but not in giraffes or pronghorn antelopes (which clash horns, but do not head-butt), suggesting that pachycephalosaurs did indeed head-butt. The computer simulations also suggested that Stegoceras could withstand considerable impacts to its skull, further supporting the head-butt hypothesis.

A CT scan of the skull of Stegoceras, showing areas of high and low density bone.

All this suggests that pachycephalosaurs, and Stegoceras in particular, did indeed engage in head-butting behavior. It does not settle the debate - it is more-or-less impossible to completely determine the behavior of an animal that has been extinct for tens of millions of years - but it does counter the argument that the skull structure was wrong for head-butting. In fact the skull appears to be so well adapted to head-butting that any other behavioral theory would need to suggest an alternative reason for the structure. It does not counter the argument that the 'S' shaped neck of Stegoceras would be unsuitable for head-butting in the manor of a goat or musk ox; but Stegoceras was neither of those creatures. Woodpeckers also have 'S' shaped necks, and engage in impressive head-butting behavior (though it is unlikely that Stegoceras closely mimicked this behaviour either).

See also An Australian Spinosaurid,
The Ashdown Maniraptoran
and Dinosaurs on Sciency Thoughts YouTube.

Tuesday 28 June 2011

An Australian Spinosaurid

In May this year (2011) a team lead by Paul M. Barrett of the Department of Palaeontology at the Natural History Museum in London published a paper in the journal Biology Letters in which they report the discovery of a single cervical vertebra (neck bone) of a spinosaurid dinosaur from the Early Cretaceous of Victoria, Australia. This is the first reported discovery of a spinosaurid dinosaur in Australia.

The Spinosaurid cervical vertebrae. Scale bar = 20 mm.

The spinosaurids are an unusual group of theropod dinosaurs with narrow elongate snouts that have been compared to those of crocodiles. Palaeobilologists have suggested that they may have fed in a similar way to modern crocodiles, preying on fish and small animals in an aquatic environment. Isotopic studies of the bones of spinosaurs have also suggested they spent much of their time in the water. The group takes its name from the first species discovered, Spinosaurus, which had elongate spines on its thoracic vertebrae (back bones), although these spines have not been found in other species, so the name is slightly misleading. It is theorized that the spines in Spinosaurus supported either a sail-like structure (popular with dinosaur artists and the popular press) or a camel-like hump (popular with palaeobiologists).

An artist's impression of Spinosaurus by dinosaur artist and palaeontologist Lukas Panzarin.

The spinosaurs belong to a larger group of theropod dinosaurs called the Megalosauroidea, which groups them with the megalosaurs (unsurprisingly) and a few other species that are apparently closer to these two groups than they are to the Avetheropoda, the group which includes allosaurs and birds. The spinosaurs appeared in the mid Jurassic and became fairly abundant in the early Cretaceous. They are not known from the later Cretaceous, though some isolated teeth of possible spinosau origin have been found.

The Australian specimen closely resembles a neck vertebrae from Baryonyx walkeri, a species known from the Early Cretaceous Wealden Beds of Southern England, though sensibly Barrett et al. have not attempted to assign a species to this single bone. A Baryonyx specimen from the Wealden beds was found with fish scales in its stomach, further supporting the aquatic lifestyle theory for spinosaurs.

An impression of Baryonyx walkeri by dinosaur artist Adam Stuart Smith.

The specimen was discovered in the Eumeralla Formtion, part of the Early Cretaceous Otway Group, to the east of Crayfish Bay, Victoria. The Eumeralla Formation is a series of mudstones, siltstones and volcanogenic sandstones, thought to represent a floodplain with meandering rivers, swampland and many shallow lakes.

Barrett et al. also note that the absence of spinosaurs, and other groups, from Australia has been used in the past to support theories about the break up of the ancient supercontinent of Gondwana, on the basis that groups absent from a particular chunk of the former landmass indicate that the piece in question had split off from the main before that species had emerged. Barrett et al. dismiss this approach since as we discover more about ancient faunas, we increasingly find species in places where we had thought that they were absent, and that even if we do not find evidence for the presence of a species, that does not mean it was not there.

See also The Ashdown Maniraptoran,
Head-Butting in a Pachycephalosaur
and Dinosaurs on Sciency Thoughts YouTube.

Monday 27 June 2011

Asteroid 2011MD

At about 5.00 p.m. Greenwich mean time today (27th June 2011) Asteroid 2011 passed over Australia, Southern Africa and Central America at a distance of about 12 000 km or 32 times as close as the moon, which sounds pretty close, but, to give a sense of proportion, is also 36 times as far from the Earth as the International Space Station.

The asteroid was discovered five days previously (on the 22nd June) by the Lincoln Near-Earth Asteroid Research (LINEAR) project in New Mexico and given the designation 2011 MD, which means the fourth asteroid discovered in the period 16-30 June 2011. For the purpose of naming asteroids the year is split into 24 half month periods, numbered A to Y (I is not used).

An image of 2011MD, a faster moving streak against the background of stars.

2011MD is thought to be a house sized chunk of rock, between 10 and 45 meters across. This is small enough that it would break up in out atmosphere; small chunks might reach the ground but it would be unlikely to do any significant damage. Nevertheless reports of the near miss in the popular press have been peppered with stories about dinosaur killing asteroids. These step from the 1980 theory proposed by physicist Luis Walter Alvarez that the mass extinction 65 million years ago at the end of the Cretaceous Period, most noted for the loss of all non-avian dinosaurs, was caused by a massive meteorite impact, and the subsequent discovery of a global iridium layer at the same stratigraphic level by his son Walter Alvarez. This theory was popular throughout the 80s and 90s, particularly after the discovery of an impact crater off the Yucatan Peninsula in Mexico which seemed to fit the bill. Subsequent study by geologists has suggested that this crater is in fact to early to mark the end of the Cretaceous, and the impact theory in general is not as widely supported in the geological community as might seem to be the case to an outsider. Many geologists feel that volcanic activity associated with the collision of India and Asia, particularly the massive Deccan Traps flood basalts, may have caused a catastrophic climatic breakdown which caused the extinction. However the impact theory has rather more 'Hollywood' appeal than the volcanic one so it remains the theory most likely to be seen in the popular press, and it is still widely supported by astronomers and astrophysicists, partly out of tribal loyalty, and partly because they do not tend to follow geological journals closely.

Almost certainly not how the dinosaurs died out.

This is not to say that a sufficiently large asteroid impact couldn't cause devastation on such a large scale, or indeed far, far worse. The moon is thought to have been produced as the result of a collision between the Earth and a Mars-sized planet over four billion years ago, but as the solar system has aged the number of large objects floating about has steadily decreased; the odds of such a large impact happening now, let alone with an object we had not yet seen, are vanishingly small.

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Thursday 23 June 2011

The Newton Abbot Earthquake.

The terms 'Newton Abbot' and 'Earthquake' do not usually go together, but at a quarter to two this afternoon (Thursday 23 June 2011) the Devon town was shaken by an Earthquake with a magnitude of 2.7 on the Richter Scale. People in the town and neighboring villages reported a bang similar to a sonic boom, followed by houses shaking. There are no reports of any significant damage or injuries.

Seismogram of the Newton Abbot Earthquake, from the British Geological Survey.

Normally a magnitude 2.7 Earthquake would pass without notice, detected only by seismometers (the UK is hit by about a dozen earthquakes of this magnitude every year), but this one was close to the surface, at a depth of 1.5 kilometers. For comparison the recent Earthquakes in New Zealand have been at depths of between 5 and 10 km and the devastating earthquake that hit Fukushima in Japan earlier this year was at a depth of 10 km. Earthquakes lose energy rapidly as they pass through the Earth, so they are most powerful close to their hypocenter (the centre of the earthquake, as opposed to the epicenter, the point on the ground above the hypocenter) so they have they are most dangerous to humans when this hypocenter is close to the surface - where we live.

The UK is not a notoriously earthquake-prone country, but we do have a few, and some bits of the country are more earthquake prone than others. The more earthquake prone areas are Cornwall, South-West England, the West Midlands, Wales, North-West England, Yorkshire, Western Scotland and around the southern English cities of Chichester and Dover. The last recorded fatality in a UK earthquake was in 1940 when an elderly lady in Wales fell down a flight of stairs during an earthquake.

The UK is far from an active plate margin, but it is not stationary, it is being pulled across the surface of the Earth by the movement of the plates. Several different plate motions effect the UK. Firstly the Atlantic sea-floor is spreading, with new material being created along the Mid-Atlantic Ridge, pushing North America to the west and Europe to the East. Then Africa, India and Australasia are pushing into Eurasia from the south, pushing the continent northwards; however Eurasia stretches more than half way round the northern hemisphere, so it cannot be pushed evenly north without something giving. Then the North Sea Basin is still expanding, pushing the UK westwards. It is also possible that the UK is still rebounding from the last Ice Age; in geological terms millions of tonnes of snow and ice were removed from the surface of the UK a mere eye-blink ago, so it is not surprising that the country is bobbing up and down a bit. This is of course most pronounced in Scotland; it is not clear if earthquakes in southern England can be attributed to this cause.

A map of Earthquakes in the UK, also from the British Geological Survey.

Monday 20 June 2011

The Ashdown Maniraptoran

This May's edition of the journal Cretaceous Research saw a paper by Darren Naish and Steve Sweetman of the School of Earth and Environmental Sciences, University of Portsmouth in which they describe a neck vertebrae from a maniraptoran dinosaur. This was discovered by fossil collector Dave Brockhurst, at the Ashdown Brickworks Quarry at Bexhill in Sussex, and has been dated as belonging to the Valanginian Age (Early Cretaceous), or as being about 140 million years old(ish). If the identification is correct then this will be both the first maniraptoran dinosaur discovered in the UK, and one of the smallest non-avian dinosaurs (i.e. dinosaurs that are not birds) ever discovered.

The single bone from which the Ashdown Maniraptoran was described, seen from a variety of angles.

Dinosaur finds have a reputation for being the only kind of scientific discovery that sells newspapers, and the story duly appeared in a number of papers (e.g. the Mirror, The Daily Mail, Huffington Post), though most of these relied heavily on the University's original press release. This is fair enough, vertebrate palaeontology is a fairly technical subject, and few papers have science corespondents equipped for in depth analysis. The fossil has also been discussed on specialist palaeontology blogs, such as those of senior author Darren Naish or dinosaur artist Matt Martyniuk, though these tend to be quite technical and aimed at other vertebrate palaeontologists. Thus there is a lack of a non-technical discussion of this (fairly remarkable) paper; one which having a background in palaeontology (though not dinosaur palaeontology) I shall attempt to fill.

What is a Maniraptoran?
The maniraptorans are a group of predominantly small theropod dinosaurs, including birds and those groups closely related to them; as such the maniraptorans are not extinct, though all non-avian groups died out during the Late Mesozoic (at least 65 million years ago). When palaeontologists talk about this fossil being the first maniraptoran fossil from the UK they are referring to non-avian maniraptorans.

The maniraptorans are distinguished by having a calcified breast bone (as opposed to a cartilage sternal plate), an elongated, three fingered hand, and a half-moon shaped bone in the wrist. The non-avian maniraptorans were the first group of dinosaurs in which feathers were well described, from remarkably well preserved fossils from Lioaning Province in China, although these have now been found in a wider range of dinosaur groups. Several groups have backwards-facing, bird-like hips.

The maniraptorans comprise six main groups, and a few extra specimens which don't fall precisely into any group. Their classification is likely to change in the future; many maniraptorans are small and known only from fragmentary remains, it is quite possible that new specimens will emerge that cause dinosaur specialists to review their current classification.

The Therizinsaurs are a poorly understood group with bird-like hips and adaptations for herbivory, they had three large, elongate claws on each hand, and specimens with feathers have been found. The smallest therizinsaurs were slightly over two meters long, the largest about twelve meters, and weighed over six tonnes (big for a theropod dinosaur. They were known only from fragmentary remains till the mid 1990s, and subsequently were variously classified as theropods, prosauropods of ornithischians.

Reconstruction of the Therizinsaur Beipiaosaurus, by artist Matias Bofarull Oddo.

The Alvaresaurs are a group of small dinosaurs with elongated rear limbs and snouts (with very small teeth), and reduced fore-limbs, though their structure suggests these fore-limbs were very powerful, with large arm and breast muscles. Feathered specimens have been found. It has been suggested that the Alvaresaurs were adapted to digging into termite mounds or similar insect structures. Many Alvaresaurs are only known from partial specimens, making detailed reconstructions difficult, but those that can be reconstructed ranged in size from about 40 cm to about 2.5 meters.

Reconstruction of the Alvaresaur Achillesaurus by artist Hodari Nundu.

The Oviraptosaurs are a group of maniraptorans with short tails, few or no teeth, and beak-like jaws. They ranged in size from about 15 cm to about 8 meters, though as with other groups many species are known only from fragmentary remains, so this range might be extended. Feathers have been discovered on specimens of several species. Some dinosaur specialists consider the Oviraptosuars should be classified as being true birds.

An artists impression of the Oviraptosaur Hagryphus giganteus. Illustration by dinosaur artist Michael W. Skrepnick.

The Avialans are the birds (Aves) plus a couple of specimens considered so close to the birds they are placed with them rather than in any other group. The two non-bird members of the group are Scansoriopteryx and Epidexpteryx. It is possible that these are the same species as Scansoriopteryx is only known from two juvenile specimens and Epidexpteryx from a single adult specimen, although Scansoriopteryx has a very long tail and Epidexpteryx a very short one, which would be an unusual growth pattern.

A reconstruction of Epidexipteryx by Qui Ji and Xing Lida.

The Troodontids have larger brains for their size than any other known dinosaur group, comparable to modern birds and larger than Mesozoic forms. They also had large forward facing eyes, and enlarged middle ears, implying acute senses. The ears were slightly asymmetric, a trait also known from owls, which suggests that they may have had a similar ability to pinpoint sounds. They had retractable or semi-retractable claws on their second toes. Troodontids ranged in size from about 30 cm to about 2.4 meters in length. Feathers are well documented in the Troodontids.

Illustration of Troodon by Dr Anne Musser of the Australian Museum.

The Dromaeosaurs were bipedal dinosaurs with well developed retractable claws on their second toes, fore-limbs that could be folded close against their bodies and elongate, rigid tails. Most if not all species appear to have been feathered and some species may have been able to fly. They ranged in size from about 70 cm to over 8 meters in length. The Dromeosaurs are often encountered in popular culture as 'raptors'.

A reconstruction of Velociraptor by dinosaur artist Michael W. Skrepnick.

Where did it live?
The fossil was found in the Ashdown Formation, part of the Wealden Group, a Lower Cretaceous sequence of rocks from southern and eastern England and running out under the North Sea. The Wealden Group represent subtropical coastal plains and shallow marine environments. The Ashdown Formation are sand and mudstones from braided river formation, possibly an environment similar to the Lower Mississippi, Senegal, Ganges or Murray-Darling river basins. On the whole smaller vertebrates have lower preservational potential than large ones, since their skeletons are more easily broken up. In an environment such as a river basis whole skeletons from small animals are unlikely to survive, but individual bones stand a good chance of being fossilized.

How confident is the diagnosis?
Claiming a dinosaur group was present in an area where it was previously unknown from a single bone is a bold step, and mistakes have been made in the past, but this does not mean the diagnosis is wrong. In the nineteenth century it was common to describe each new bone discovered and formally name it. Since precedence is important in naming fossils, this meant that a palaeontologist who had painstakingly reconstructed a complete animal could well lose the right to name this to an amateur fossil hunter who had found a single bone. Unsurprisingly this way of doing things fell into disrepute, and for much of the twentieth century palaeontologists ignored isolated bones. Naish and Sweetman are clearly aware of this, and have declined to name a species on the basis of this bone. They have, however, been able to make some deductions from the bone.

Dinosaur vertebrae are quite distinctive to a specialist, and bones from the different parts of the spine can also be identified with confidence, so the diagnosis of the bone as a neck bone from a small dinosaur is probably reasonable. The bone appears to have stopped growing, supporting their analysis of it as an adult bone, suggesting that this does indeed come from a small species, though exactly how small is hard to judge; a reconstruction based upon a typical maniraptoran gives a length of 30-50 cm, though if it belongs to a different group then this would be different. The bone has a distinctive 'x' shaped profile, which has been observed in Oviraptorsaurs, on the basis of which Naish and Sweetman conclude that the bone is a dinosaur bone, most likely to be a Oviraptosaur, and if not then likely to be a closely related Maniraptoran. It is possible that the bone does come from a different form of dinosaur, but this would be a more remarkable find, since no other dinosaur group is known to produce specimens this small, or with this bone structure.

See also An Australian Spinosaurid,
Head-Butting in a Pachycephalosaur
and Dinosaurs on Sciency Thoughts YouTube.

Saturday 18 June 2011

Snowfall in Namibia

The borders of modern Namibia were drawn up on a map at the Berlin conference of 1884, named of South West Africa, and given to Germany as a colony. The germans ruled it from then until 1915, when it was invaded by South African troops during the First World War.

Namibia. The sticky-out bit at the top (Caprivi Strip) was because the Kaiser (german king) wanted his colony to have a view of Victoria Falls.

During the period 1884-1915 the Germans built farms, exploited the county's vast mineral wealth, and drove the indigenous population off the land wherever possible. Many settlers arrived during this period and they did their best to re-create their homes, building faithful reproductions of german houses in the deserts of southern Africa. Many of these buildings followed the traditional style of the German Alps, with steep roofs to prevent the snow piling up, something of a rarity in the area, but a popular tourist attraction a century later.

A row of historic shops in Windhoek, Namibia, with steep roofs to prevent snow accumulation, combined with an open bar on the roof of one building.

In June this year (2011), snow did indeed fall in Namibia. Images of this snow quickly made their way onto the internet, leading to much speculation around the globe, and the emergence of some interesting theories online, which can be quickly ran through.

1) This is a sign that the end of the world is immanent, as prophesied in the Book of Revelations. Basically we're all doomed, though there are a few religious organizations (or at least organizations which claim to be religious) offering salvation in return for large, and prompt, cash donations.

2) This is a sign that the end of the world is immanent, as prophesied in the writings of the ancient Mayans. Unfortunately the ancient Mayan priestly class are no longer with us, so it is unclear if they could have offered salvation in return for cash, or anything else. What we do know of their religion suggests that they may have thought a human sacrifice on top of a large pyramid was worth a go.

3) This is a sign of global warming, normal weather patterns are breaking down and freak weather events are becoming more likely. This is certainly a lot more plausible than either of the previous explanations, and there certainly has been an increase in freak weather conditions in the last few years, which may well be linked to global warming. Yet while climate models used to predict the outcome of various warming scenarios do predict a wide range of extreme weather events becoming more common, I am not aware of any that predict snowfall in the Namib Desert. From a scientific viewpoint just saying 'more freak weather' conditions is not very satisfying, this is just invoking the bogeyman to explain anything we don't have an answer for; as a scientist one should look for more direct explanations.

4) This is a sign that global warming is not happening, all climate science is complete hogwash, and we cannot predict the weather in any meaningful way. There will always be weather events that happen outside our expectations, and we should stop worrying about it. This is more of a political viewpoint than a scientific explanation, it rejects an explanation that its adherents do not like, but offers no explanation for events, indeed it rejects the idea that we should look for explanations - profoundly unscientific.

5) It snows in Namibia, this is not a freak weather event, but an uncommon one, entirely within Namibia's normal conditions.

Actually it does snow in Namibia from time to time (the last snowfall was in 2006), but this is a rare event. and there is only ever a light sprinkling, never enough to collapse anybody's roof. Namibia has a subtropical climate with two seasons; a short, hot, wet season, and a longer, cooler, dry season. The wet season is to hot for snow, and the cool season far to dry (and as a rule, still to warm). So the snow still needs a bit of an explanation.

The snowfall in Namibia, not actually that dramatic.

So if snow in Namibia is an unusual event that requires an explanation, then it is logical to look for other unusual events that happen at roughly the same time. This year has seen a number of dramatic weather events, from floods in Australia to tornadoes in New England, but these are effects rather than causes, and, unlike the Namibian snow, they are all events that have been predicted by the models of climatologists studying global warming. There have also been earthquakes in Japan and New Zealand, but again it is difficult to see how these could cause snow in Namibia.

More interestingly there have been two significant volcanic eruptions this year; Grímsvötn in Iceland and Puyehue kin Chile. Grímsvötn is in the northern hemisphere, too far from Namibia to have had any significant effect on the climate, but Puyehue is ideally placed to cause precipitation in southern Africa.

Volcanoes are not obviously wet objects. We associate them with ash and heat, but volcanic plumes actually contain a considerable amount of water vapor. The volcanoes of South America are fed by the subduction of the Pacific Plate beneath the South American Plate. As the waterlogged sea-floor is pushed deeper it is warmed by the internal heat of the Earth. This eventually forces the water out of the sinking crust, and it rises up through the overlying South American Plate, carrying superheated liquid rock with it. Eventually it emerges in the Andes, forming volcanoes such as Puyehue. This superheated water vapor explodes far into the atmosphere, carrying the more obvious volcanic ash with it (gaseous water vapor is invisible). Once this reaches the upper atmosphere it is carried eastward by the Earth's motion (the ground rotates more rapidly than the upper atmosphere, so anything in the upper atmosphere is carried eastward). The majority of the Puyehue plume has passed to the south of Africa, eventually traveling round the world to disrupt air travel in Australia and New Zealand, but enough material has spread over southern Africa to have an effect (there has been snowfall in South Africa as well, but this is less unusual, and so has escaped comment). In addition to the water vapor the volcano will have produced significant amounts of sulphur dioxide (SO₂) into the upper atmosphere. This (in addition to other effects) acts as a cooling agent, facilitating but not guaranteeing snowfall.

As a theory this is all very well, but to make a strong association between volcanoes in South America and snow in Namibia we would need more than one example. The last time it snowed in Namibia was in February 2006, this time during what should have been the warmer season. This was a month after the onset of volcanic activity at Galeras Volcano in Chile, hundreds of kilometers to the north of Puyehue.

An areal photograph of the Galeras caldera. To the lower right a smaller plume comes from a fumarole, a small vent through which only gas escapes.

Unfortunately I do not have details of every recorded snowfall in Namibia at my fingertips, so I am unable to check them against volcanic eruptions in South America, however the small sample have been able to check suggests that snow in Namibia is usually preceded by volcanic eruptions in South America, although the reverse is not true; not every volcanic eruption in South America leads to snowfall in Namibia.

See also The Puyehue-Cordón Caulle Volcanic Complex,
The Puyehue Eruption, Chile, 2011.

Thursday 16 June 2011

The Christchurch Earthquakes

On the 4th of September 2010 at 4.35 in the afternoon an earthquake with a magnitude of 7.1 on the Richter Scale occurred at a depth of about 10 km beneath the town of Darfield, roughly 40 km west of Christchurch, New Zealand. Despite the size of the earthquake destruction was minimal, as most buildings in the area are re-enforced against earthquakes, and there were few casualties; two people were seriously injured, and one died as a result of a heart-attack which was almost certainly brought on by the quake.

The Richter scale is based upon the logarithm of the amplitude of the waves that make up the earthquake; the maths behind this is a bit complex, but the logarithm bit is important. A logarithmic scale records orders of magnitude, that is to say 2 is ten times as much as 1, 3 is ten times as much as 2 etc. this means that a huge range of wave amplitudes can be recorded on the scale without getting into huge numbers. Seismometers cannot directly detect large earthquakes (they break), so the magnitude of larger earthquakes is calculated from readings on several remote seismometers, or in the case of very large earthquakes, by calculating backwards from the amount the rocks have moved. This means that the scale is not absolutely reliable; it is a useful tool for geologists - and journalists - but there can be rival claims for the strongest earthquakes.

The magnitude of an earthquake is measured at its central point (hypocentre), which can be a long way beneath the ground, thus earthquakes higher on the Richter scale are not necessarily the most destructive, those close to the ground are the most dangerous. An alternative system of measuring earthquakes, the Mercalli Scale, measures earthquakes by their effects; this is measured at the epicentre of the earthquake, i.e. the point on the ground above the hypocentre. This has downfalls of its own, since cities that expect earthquakes tend to be better prepared than those that do not; an earthquake that would flatten London or New York can be endured by Tokyo or Los Angeles.

On 22nd February 2011 a second earthquake struck, this time 2 km west of Lyttelton, a town 10 km south east of Christchurch. This earthquake had a magnitude of 6.3 (i.e. it was roughly a tenth as strong as the first earthquake) and occurred at a depth of about 5 km. This was much more destructive, significant soil liquidification occurred in the eastern suburbs of Christchurch (the soil was shaken so much that it behaved as a liquid), leading to considerable damage to property and the loss of 181 lives. Geologists are still undecided as to whether this was an aftershock of the first earthquake or a separate event.

Damage to Christchurch's Catholic Cathedral following the February 22 Earthquake.

On the 16th April an earthquake with a magnitude of 5.3 occurred 16 km east-south-east of Christchurch at a depth of 9.2 km. This lead to power outages and further damage to property, but no casualties.

On the 10th of May another earthquake struck the region, this time with a magnitude of 5.3, roughly 4 km beneath the town of Rolleston, 20 km to the south-west of Christchurch. Again this caused damage to property but no casualties.

On the 6th of June a second earthquake struck Rolleston, this time with a magnitude of 5.5 but at a depth of 15 km. This caused further damage to properties, but no serious injuries or loss of life.

On the 13th June an earthquake, with a magnitude of 5.7 struck Taylor's Mistake, 10 km south-west of Christchurch, at a depth of 9 km. This was followed by an earthquake under the sea 10 km east of the city, with a magnitude of 6.3 and at a depth of 6 km. These earthquakes caused considerable more damage to property, and resulted in a number of injuries.

All of this has left the people of Christchurch somewhat concerned for the future of the city. Prior to 4th September 2010 there had not been an earthquake of any size in the area since 1922, and now there does not seem to be an end to them.

New Zealand is a seismically active country; it lies on the border of the Pacific and Australian tectonic plates, a convergent boundary where the Pacific Plate is being forced under the Australian at a rate of about 40 mm a year. The country has over forty active volcanoes, and is has around 15 000 earthquakes a year, though most of these are to small for anyone to notice them.

Earthquake prediction is far from being a precise art, but it is safe to predict that if you are on an active fault and have not had an earthquake for a while, then you are likely to have one. The progress of one plate over another is not a smooth process, rocks rubbing against one-another typically move in stops and starts, as the plates move the rocks catch on one another. Stress then builds up within the rocks until they give way, and the plate rolls on. The long period of time that Christchurch has been without an earthquake implies that the rocks beneath it were likely to be very stressed. The earthquakes that have occurred will have released a lot of this stress, possibly all of it. At some point the earthquakes will stop and life in Christchurch will return to normal, though it is impossible to say if this will be tomorrow or in five years time.

Christchurch's situation is made worse by its location on the south-east coast of New Zealand, as this is where the tectonic boundary is at its shallowest. The boundary between the plates runs roughly south-west to north east along the whole of New Zealand. On the southern coast around Christchurch it is only five to ten kilometers beneath the surface, on the far coast it is closer to 500 km deep. This makes earthquakes on the south-east coast far more dangerous than those on the north-east.

A rough diagram of a cross section through New Zealand's South Island (not to scale), showing the depth of the plate boundary beneath the country.

Monday 13 June 2011

The Puyehue Eruption, Chile, 2011.

Puyehue is a stratocone volcano (i.e. a cone-shaped volcano of the kind seen in Hollywood movies) in central Chile. It forms part of the Puyehue-Cordón Caulle Volcanic Complex, along with the Cordón Caulle volcanic fissure and Cordillera Nevada caldera. Puyehue began erupting on June 3rd this year, the complex having been dormant since 1960, when, following an earthquake with a magnitude of 9.5 on the Richter scale (the largest earthquake ever recorded), the Cordón Caulle fissure erupted throwing ash eight kilometers into the air.

See The Puyehue-Cordón Caulle Volcanic Complex.

It is not clear what part of the volcanic complex the eruption occurred in - the complex is rather remote - it could be Puyehue itself or the Cordón-Caulle fissure. There has been an evacuation of the immediate area, although it is unclear what proportion of the population has actually left.

The ash cloud is proving to be far more disruptive than the volcano itself; this has caused heavy ash-falls in neighboring Argentina and Uruguay, leading to power failures as ash settles on power lines and brings them down, as well as the closure of airports in all three countries. The Argentine army has been dispensed to the area to help with the clean-up operation.

From South America the ash-cloud has spread east across the southern ocean (ash clouds entering the upper atmosphere always spread to the east, as this part of the atmosphere does not rotate as fast as the solid Earth; effectively the ash stays still while the planet moves beneath it), missing the tip of Africa then arriving in South East Australia and New Zealand, where it is causing considerable disruption to air traffic. Most airlines affected have agreed to follow guidelines and remain grounded while the crisis lasts, but worryingly Air New Zealand appear to be following the lead of British and Irish airlines and are proposing to fly during the crisis, hoping to dodge the ash clouds. Volcanic ash is particularly dangerous to jet aircraft as the fine ash can melt inside the hot engines, coating their innards with volcanic glass.

Satellite image showing the progress of ash from the Puyehue eruption (false coloured in yellow) around the southern hemisphere.

In addition to the ash cloud a pyroclastic flow (avalanche of hot volcanic material) has apparently reached the Nilahue River, raising the temperature from 10°C to 45°C and causing a mass die-off of salmon. Other rivers in the area are reported to be partially blocked by ash, leading to some flooding of farmland; there are no reports of any urban areas being threatened, nor have there been any reports of loss of life directly connected to the volcano.

The volcanic cloud has produced some spectacular lightning displays. These occur when convection currents in within the cloud carry particles with different charges apart; eventually the charge differential becomes to great and an electric discharge occurs.

See also The Grímsvöten Volcano and
Volcanos on Sciency Thoughts YouTube

Sunday 12 June 2011

The Protostar HOPS-68

HOPS-68 is a protostar located in the Orion Nebula, 1450 light years from Earth. Stellar nebulae are vast cloud of gas and dust floating in space, thought to have been formed by the deaths of earlier stars. Protostars are areas within stellar nebulae that have started to fall in on themselves due to gravity; effectively new stars being born.

Protostars have a roughly whirlpool shaped structure, with a disc of material being sucked in and accreted onto the forming core (this is a vast oversimplification). Due to gravitational effects, not all the material falls directly onto the new star; some of it is slung out in two massive plumes at the north and south poles. These are usually the only visual features of protostars, since the core remains hidden at the centre of a dark accretion disk, but the superheated plumes can stick out far (sometimes light years) on either side.

An artist's impression of a protostar.

On April 19 this year a paper appeared in the Astrophysical Journal Letters from a team lead by Charles Poteet and Thomas Megeath of the University of Toledo, detailing the results of a spectrographic study of the Protostar HOPS-68 using the Spitzer Space Telescope. This found the presence of the mineral forsterite (Mg2SiO4), a form of olivine, apparently being ejected in the plumes then falling back into the accretion disk. Poteet et al. theorized that this was forming in heat caused by friction between atoms and molecules in the inner part of the accretionary disk.

Olivine is a common mineral in both the Earth’s crust and in meteorites, it is a mixture (technically a solid solution) of magnesium silicate (forsterite, Mg2SiO4) and iron silicate (fayalite, Fe2SiO4). Olivine is greenish in colour, and there have been some news stories and pictures of green crystals around HOPS-68. In fact it is the iron that gives olivine its green colour; forsterite, which lacks iron, is colourless.

Colourless forsterite crystals.

Olivine forms at relatively low pressures. It is one of the most abundant minerals in the Earth’s crust and upper mantle, but bellow a depth of 400 km magnesium-iron silicate forms different minerals, depending on the depth; these can be used to infer the depth at which rocks formed. Only the olivine form is ever found in meteorites.

Olivine has long been known in meteorites, and was found in the comets Wild 2 and Temple 1 by the Stardust rocket space probe, so its discovery around a protostar was not that much of a surprise. It had previously been thought that meteors containing it might be remnants of larger bodies, which could have had a liquid phase similar to terrestrial lava or magma in their evolution, but comets are mostly ice, and are thought to stem from a much earlier stage in the solar system’s evolution, they are remnants of our own protoplanetary disk; geologists can date rocks by a variety of techniques, and do not believe any olivine found in our solar system predates the system itself. Poteet et al.’s suggestion that olivine crystals could form by friction within the central part of an accretionary disk very early in a solar system’s evolution, then be ejected into other parts of the disk would solve this problem.

See also; Could there be life on Gliese 581d?,
Stars on Sciency Thoughts YouTube,
Exoplanets on Sciency Thoughts YouTube.

Friday 10 June 2011

Economics for Dogs (may also be useful for politicians and economists).

My dog, like many, enjoys fetching sticks. She is not interested in balls, or frisbees, but will chase a stick all day long. For her (or possibly me) the ideal stick is straight, 2-3 feet (60-90 cm) long and about an inch (3 cm) thick; the sort of stick I can throw the furthest.

The Canine Economist, with a stick.

She clearly places value on appropriately sized sticks, since she will go to some lengths to find one, and if she cannot find a suitable stick for me to throw, will sometimes chew larger sticks to the correct size (yes, tool use in dogs, you read the unsubstantiated claim here first folks). Yet she quickly learnt that if she does not bring the stick back to me then I will not throw it for her again, so while she might play with a stick for a bit after each throw, she will always return it. Similarly she understands that once it is time to stop playing then the stick has no further value, so once I take her lead out of my pocket she loses all further interest in the stick, drops it and returns to my side.

That's about as far as economics goes for dogs. The stick has value only while it is in the game. If I stop throwing it or she stops brining it back, then it loses its value and becomes just another piece of wood. Humans use a slightly more sophisticated system than sticks, called 'money'. Unlike sticks, money can be exchanged for other items, such as tins of food or rubber bones, and can be saved for a while before it is used; but, like sticks, it has no value in itself, it must be passed backwards and forwards to gain value.

Money is quite important to governments, as they are the ones who issue it. The ability to issue money gives governments a lot of their authority, they cover it in things that are important to them, such as reigning monarchs or dead presidents; we judge how important governments are by how much we trust their money. A government which cannot issue money is just a bunch of people making up rules for other people to live by. Such governments tend not to survive long.

This being the case, we would expect governments to be keen to keep money in circulation, but a strange thing has been happening in western countries in the last few years. Governments have come to accept that economics can have winners and losers, that it is reasonable for some people to collect all the money and keep it, and wrong for them to intervene and stop this happening. Thus we have seen a situation develop where a few people come to own more and more of countries assets, while at the same time paying less and less tax, while the rest of the population own less and less of the countries assets, and pay more tax or face cuts in public service because the government can no longer 'afford' them; governments who do not tax the rich end up having to borrow money from them to run services, then having to pay this money back with interest.

Many people feel that this is morally wrong, that there is something inherently wrong about a tiny minority of people living in immense wealth while many other people live in terrible poverty. Other people (usually rich ones, or ones who work for rich ones) argue that this is wrong, that the rich deserve their money as they have in some way earned it, and that it would be morally wrong for governments to take money away from them.

All this rather misses the point. Money, like sticks, only has a value because it moves back and forth. If this stops happening then people lose faith in money, and the governments that issue it. The assumption currently being made is that if money is taken away from ordinary people, then since they need it they will work hard to get more. This might work for a bit, just as when I take a stick from my dog she will find another one, but it can't work for ever, if I keep taking sticks from my dog she will lose interest and do something else.

Because money only represents other things, new wealth can only really be made in a limited number of ways. Either we can harvest things, through farming, mining, fishing, forestry etc., or we make things, such as cars, houses, software or music, we then trade those things for money, and the money for other things. If you take the money away people don't keep trying to get money for ever, they eventually give up and trade without it (or in another country's money that they can get hold of). When this happens they lose they stop paying taxes, which tends to bring them into conflict with governments.

Twenty years ago, when I worked in mineral exploration in West Africa, I got to see this first hand for myself.

Most African countries had very weak economies, so they either had weak currencies (most former British and Portuguese countries), relied on another country to support their currency (most former French colonies, where the CFA Franc was tied to the French Franc, and had a value dependent on the French, rather than the African, economy) or simply didn't bother having a currency at all (Liberia, where US dollars were legal tender. and the only money issued by the government was commemorative coins aimed at collectors).

Most African countries were also heavily in debt. Western (and Soviet) banks had leant large sums of money to African leaders (who were seldom chosen by their own people) who either spent the money on ill-conceived development projects (often on the advice of the banks) or just on plain high living. Now the banks were demanding repayment that governments could not afford. Much of the money in many countries was hoovered up for debt re-payments, which often didn't cover the interest on the loans. Many governments were pressured into selling off national assets on the cheap just to keep up with payments. Governments became agencies of overseas creditors, unable to provide services for their people, but expected to rule their countries for the benefit of outsiders.

According to economic theory the people of these countries should have worked harder to raise the money to pay off the debt. In practice they simply had no means of doing so. Unlike in the West most people in Africa have access to land on which to grow their own crops, so lack of money does not spell immediate starvation. Similarly most locally made products come from craftsmen's workshops rather than large scale factories. So when the money dried up (or lost its value), they simply returned to a system of barter, or used foreign currencies or contraband goods (the black market). But it is not possible to found new industries on any scale in a barter economy, and when things go wrong the safety net we expect in the West does not exist. Thus if you got sick there was no hospital, when you were a victim of crime the police could not be trusted because they earned too little to live, and when crops failed, people starved.

This eventually lead to some countries completely collapsing. In the absence of any meaningful government civil wars were fought between factions who were little more than criminal gangs. Wars in Liberia, Sierra Leone and Somalia were financed by smuggled gold and diamonds, illegally exported timber, piracy on the high seas, even exporting videos of prisoners being tortured.

Fortunately for Africa many people saw this for the madness it was. The Jubilee 2000 Campaign, a loose alliance of charities, churches, rock stars and academics, founded by Martin Dent, a former lecturer in politics at the University of Keel in the UK campaigned for African debt to be cancelled, and, unusually, politicians listened. Debts owed by African nations to developed nations were cancelled, those to private institutions quietly paid off (this may have been a mistake; many organizations came to the conclusion that if African nations could be pushed back into debt Western governments would pay it again).

Rather than learning from this, a new generation of politicians has emerged in many Western nations that seems keen to import the problems formerly faced by Africa to Europe and North America. Taxes paid by wealthy individuals and corporations (which were getting dangerously low twenty years ago) have been cut to the bone, and nations have gone into debt as a consequence. The ordinary population, having faced years of pay-freezes or even cuts, are being told they must pay more tax and accept less services from their governments. Like Africans of an earlier generation Westerners are told they must work harder for less in order to pay off the debts, but have no realistic chance of doing so without the political will. In fact the countries slashing services the hardest, such as the UK and Ireland, are heading further into debt more rapidly.

Of course the West is not Africa, and things cannot be expected to play out the same way. Few people have access to enough land to feed their families, and few goods used by Westerners are made by local craftsmen. This reduces people's ability to fall back on barter as a means of coping without money; i.e. things can potentially get worse much more rapidly in the West than in Africa. Many Western countries have developed strong parallel economies based around our favored form of contraband (narcotics). Mexico is close to a state of civil war, not over any political issues, but due to violence between narcotics gangs; gangs which do not even supply the Mexican market, but that of the US. America itself is greatly troubled by narcotics related violent crime, as are many other Western nations.

Ultimately Western nations are mature democracies. People expect their governments to be accountable, and if they are not, to be able to get rid of them. There is every possibility that the next few years could be rather bumpy, but ultimately we should get through this. But every time I hear a politician claiming that everything else must be cut to pay off debts, or that its OK for the wealthy to avoid taxes the rest of us have to pay, I can't help but think 'My dog knows more about economics than that!'.

Monday 6 June 2011

The Puyehue-Cordón Caulle Volcanic Complex

The Puyehue-Cordón Caulle Volcanic Complex is in southern Chile, about 450 miles south of the capital Santiago, and about 20 miles west of the Argentine border. Chile has about 3000 volcanoes running from north to south along the whole length of the country, which about 80 are still periodically active. These occur as the Nazca Plate (part of the Pacific sea floor) is forced below the South American Plate; the South American plate is lifted up, forming the Andes Mountains, as the Pacific Plate is subducted into the Earth's mantle lighter minerals are melted and bubble up to the surface, creating a string of volcanoes throughout the Andes. The Andes are among the fastest growing mountains on Earth, and were where mountain orogeny (the growth of mountains) was first understood.

View Larger Map

The Puyehue-Cordón Caulle Volcanic Complex lies on the Liquiñe-Ofqui Fault, where the Nazca, South American and Antarctic Plates collide, an area of intense volcanic activity. The Puyehue-Cordón Caulle Volcanic Complex itself is between 200 000 and 300 000 when a shift in the fault shifted to the east and narrowed. A series of older volcanoes to the east all ceased activity at this time, and were replaced by younger larger volcanoes such as Puyehue-Cordón.

Technically Puyehue is a stratocone volcano, i.e. a classic cone-shaped volcano, whereas Cordón Cauelle is an adjacent volcanic fissure. The volcanic complex is very active, with a record of observed eruptions going back to 1759 when the first permanent European settlements in the area were established. There were nine eruptions during the twentieth century, including one in 1960 associated with the May 22 Valdivia earthquake, the most powerful earthquake ever recorded.

The complex began to erupt again on the 4th of June this year (2011), an eruption accompanied by a swarm of earthquakes and throwing an ash-cloud high into the air. It is not yet clear if this originates from the Puyehue stratocone or the Cordón Cauelle fissure, due to the remote location of the complex, within the Puyehue National Park and the fact that it is mid-winter in the southern hemisphere in June.

The Chilean government has responded by ordering the evacuation of around 3000 people from the area around the volcano, although it is unclear how many people have actually left; the raising livestock is an important part of the local economy and people are often reluctant to leave their animals.

The ash cloud has blown eastward over Argentina where two small airports servicing ski resorts among the extinct volcanoes of the eastern Liquiñe-Ofqui. Unlike British and Irish airlines, Argentine ones seem happy to accept that volcanic ash-clouds are dangerous to aircraft.

See also The Puyehue Eruption, Chile, 2011.
The Grímsvöten Volcano and
Volcanos on Sciency Thoughts YouTube