Month: May 2008

A drop off the old block?

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It is not so long ago that detachment and foundering of material from lithospheric blocks began to be visualised as a means to explain large areas of recent, rapid uplift of the continental surface. Chunks falling from the subducted slabs beneath Tibet and Kamchatka (see Evidence for slab break-off in subduction zones in EPN September 2002) may have generated unusual magmatism or stopped volcanism respectively. Massive Himalayan uplift and that of areas such as the Sierra Nevada in the western US seem to indicate foundering of large masses of mafic rocks from the base of thickened lower crust (see Mantle dripping off mountain roots in EPN October 2004). Even the end-Miocene Messinian salinity crisis in the Mediterranean has been ascribed to uplift resulting from delamination (see When the Mediterranean dried up in EPN May 2003). Yet convincing evidence from seismic data are conspicuous by their rarity. A necking, or monstrous boudinage of the subducting slab beneath the Hindu Kush region of the Himalayan chain is convincingly demonstrated by geophysicists from the Australian National University (Lister, G. et al, 2008. Boudinage of a stretching slablet implicated in earthquakes beneath the Hindu Kush. Nature Geoscience, v. 1, p. 196-201).

The setting for this remarkable ‘caught in the act’ phenomenon is where a minor ocean basin closed when the Kohistan arc was accreted to Asia during the closure of the Tethys ocean, and is in the process of vanishing. Wherever such minor basins have been caught up in major destructive-margin tectonics they seem to coincide with markedly arcuate orogens characterised by high-P metamorphism and repeated stacking of thrust slices. Once school of thought seeks a solution by some kind of ductile ‘dripping’ of mantle, which the authors sought to test by looking at seismicity beneath the most prominent of these arcuate mini-orogens. What they found was a zone of ‘necking’ defined by clustered earthquakes on either side. Detailed analysis suggests that a drop-shaped mass is in the process of detaching itself by a combination of brittle and ductile deformation –a boudin several orders of magnitude than any the have previously been described.

Desert varnish

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Just as vultures are annoyed by glass eyes, so geologists who use remote sensing detest vegetation cover. But the spectral blanket thrown over geology by grass and other plants is not the only irritation and one occurs where least expected. Arid terrain usually pays the best dividends in remote geological mapping, because the spectral properties of rocks and their constituent minerals emerge in reflected and emitted radiation  and bear close relationships to those determined in laboratories. Images captured from orbit that use carefully chosen wavebands are often stunningly informative in deserts. The bugbear is desert varnish, an often shiny black coating that completely masks what lies beneath, be it basalt, granite, sandstone or carbonate, even in the field. Generally it is no more than a millimetre thick, and often far thinner. Close examination often shows a minutely botryoidal texture and parallel laminae in cross section, very like a tiny stromatolite. Basically, desert varnish is such a biofilm deposit, and the responsible organisms are cyanobacteria, as in stromatolites, but exceptionally sturdy ones. However, the bulk of the material is inorganic, and it is spectrally featureless, hence the problem in remote sensing.

Widespread as it is in arid environments, desert varnish has not been deemed an appropriate subject of study, so any information is welcome (Garvie, L.A.J. et al. 2008. Nanometer-scale complexity, growth and diagenesis in desert varnish. Geology, v. 36, p. 215-218). Hailing from Arizona University, the authors are well placed. Their approach is no so much directed at organic aspects, which is a shame, but at the geochemistry of this annoying gunk. As previously known, they show the dominance of manganese phases, but mixed in with very fine-grained quartz, clays and iron oxy-hydroxides. The varnish seems to contain a wind-blown component, but the manganese and probably the iron is derived in some other way, having grain sizes less than 100 nanometres. Iron and manganese minerals dominate the fine laminae, and at very high electron microscope resolutions their grains show yet finer structure at 1 nm scale. The authors ascribe the cyclical structures and mineralogy to repeated wetting and drying, with leaching and oxidation of Fe and Mn. Both iron and manganese are multi-valent, Mn more so than Fe. For both to be leached, i.e. drawn into solution as Fe2+ and Mn2+ ions, requires strongly reducing conditions, and then oxidation to precipitate Fe3+ and Mn4+ or Mn7+ minerals. At this minute scale, whatever the source of the Fe and Mn, a biological influence seems crucial.

Renewed interest in desert varnish seems to be connected with Mars – the study was partly financed by NASA. Yet, none of the Martian remote sensing studies report annoyance with huge tracts blacked out by manganese minerals. Such surface alteration that has been analysed by the Mars Rovers proved to be iron-enriched with little significant manganese enrichment. If desert varnish is biogenically mediated, then its occurrence on Mars would be cause for excitement bordering on hysteria. The cyanobacteria in terrestrial varnishes are tough, and may date back into Precambrian times as the first colonisers of dry land. As yet, there have been no attempts to examine their genetic affinities.

New hope for very old molecular phylogeny …

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Although DNA has been obtained from a number of fossils, including Neanderthals, its complexity more or less rules out any being preserved in a useful state beyond a few hundred thousand years ago. However, information about molecular relatedness also emerges from protein sequences, albeit with less chance of detailed comparisons. Collagen from bone is a potential resource for palaeobiologists, and fossils as old as the Jurassic Period have provided useable sequences. Prime targets are large extinct animals, as the greater the mass of a bone, the better the chance that it preserves some. Two irresistible beasts are the American mastodon (Mammut americanum) and T. rex (Organ, C.L. et al. 2008. Molecular phylogenetics of mastodon and Tyrannosaurus rex. Science, v. 320, p. 499). Unsurprisingly, the research group from Harvard, Boston and North Carolina, found that a Pleistocene mastodon contains proteins closely similar to those of African elephants. The T. rex, however, has a passably close relationship to the ancestral chicken, the South Asian Red Junglefowl (Gallus gallus) and the ostrich (Struthio camelus).

In fact, both connections were expected by the team, for their research set out to show that it is possible to extract intact parts of protein sequences from fossil bones. The matches confirm their hopes, and seem set to launch attempts at resolving evolutionary relationships among vertebrates that hitherto have depended on morphology alone.

Impact cause for Younger Dryas draws flak

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Almost a year ago two dozen scientists presented evidence to suggest that onset of the Younger Dryas at 12.9 ka followed upper atmosphere explosions of cometary material (Firestone, R.B. and 25 others 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. Proceedings of the National Academy of Sciences of the United States of America, v. 104, 16016-16021; see Whizz-bang view of Younger Dryas in EPN July 2007). Evidence cited included: excess iridium; tiny spherules; fullerenes containing extraterrestrial helium; nanodiamonds and evidence for huge wildfires. Not quite the Full Monty, as neither crater nor shocked mineral grains were claimed, hence the teams’ opting for a cometary airburst. In North America such signs were said to overly the last known occurrences of Clovis tools at 7 archaeological sites (see Clovis First hypothesis dumped above). It was pretty clear that the suggestion for a hitherto unnoticed event with a widespread signature – 26 sites either side of the Atlantic were cited –  was going to be challenged, and so it has (see Kerr, R.A. Experts find no evidence for a mammoth-killer impact. Science, v. 319, p. 1331-1332), perhaps not unconnected with the blaze of publicity surrounding the paper’s appearance, including several TV documentaries.

Well, say experts, sooty layers do suggest large-scale fires, but forest fires occur every year, especially when humans are around. Fullerenes or ‘buckyballs’ equally can form terrestrially, except those containing ET helium. The last is regarded by many critics as ‘inventive’; they have never been isolated since such combinations were first reported in 2001 (see Extinctions by impacts: smoking artillery in EPN March 2002). The accepted methodology for detection of tiny diamonds seems to have been ignored, and that claimed to have found them misused. The iridium ‘spike’ – crucial in identifying the global nature of the K-T event – by itself is not enough for claims of impacts. Astonishingly, the authors cited such a Younger Dryas iridium spike in a Greenland ice core, yet the originator of those data says his paper does not report abnormal iridium at 12.9 ka or anywhere during the YD. Microspherules rain down all the time with interplanetary dust, and do not constitute sound evidence either.

So, what on Earth is going on? A collaboration between 26 authors, who willingly supply other workers with materials for checking surely cannot be conspiring at a hoax. Impact experts are hinting at ‘over-enthusiasm’ by a team outside the ‘impact community’. It all sounds oddly similar to the furore that in 1980 greeted  first suggestions by the Alvarezes for the K-T impact…

May geologists now synchronise their watches?

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Calibrating the stratigraphic column to absolute time depends, of course, on radiometrically dating geochemically suitable rocks or minerals. Yet there is a range of available methods based on decay of unstable isotopes, such as 14C, 40K, 87Rb, 147Sm, uranium and thorium. All depend on a variety of assumptions, of which that of a constant, well-established half-life is common to all. If all were perfect, several methods applied to the same materials should give the same results. The trouble is, each parent isotope favours different minerals and different compositions of igneous rocks, so that discrepancies in the dates assigned by different methods to the same stratigraphic unit may either be due to disturbance of one isotopic system relative to the other or to the half-life of one (or both) parent isotope being inaccurate. Currently, the two most widely used and best-regarded methods are U-Pb and Ar-Ar, the latter depending on 40K being converted to 40Ar by neutron bombardment. The first often uses zircons, the second various potassium minerals such as alkali feldspar. Both minerals are magmatic in origin and so the same igneous rock may sometimes be dated by either method or both. It is becoming increasingly clear that the two approaches do not give the same age, which is worrisome at the detailed level permitted by the high precision of each of the methods.

A means of checking the timing parameters for radiometric dating is to compare its results with absolute age determined by a non-radiometric method. The best-calibrated and most widely possible method that does not rely on radioactive decay is based on the astronomical pacing of climate, with its 100, 41, 23 and 19 ka cycles. Analysis of cyclicity in repetitive sedimentary sequences reveals patterns of frequencies that match the astronomical signals. So, within such a sequence it is possible to chart time differences to within a few thousand years. If there are igneous rocks interlayered with the cyclical sediments it should be possible to check their radiometric age differences against the difference determined independently. A Miocene sequence in Morocco has many intercalations of igneous tephras, and therefore provides a crucial test for radiometric approaches (Kuiper, K.F. et al. 2008. Synchronizing rock clocks of Earth history. Science, v. 320, p. 500-504). The team from the University of Utrecht, the Free University of Amsterdam in the Netherlands, and the University of California, dated sanidine (K-feldspar) from the tephras using the Ar-Ar method. This involved using a standard age determined for sanidines from a similar rock type at Fish Canyon in Colorado USA. By turning the approach on its head, i.e. by using astronomically calibrated ages for the samples, they recalculated the age of the Fish Canyon standard. It seems to be 0.65% older than previously thought (from rather dodgy U-Pb dating of  zircons in the Fish Canyon Tuff).

All Ar-Ar ages involve the Fish Canyon standard. So, an underestimate of its age would imply revision of quite a lot of geological events dated by Ar-Ar, especially those that happened abruptly, such as mass extinctions, impacts and magnetic reversals. Using the new standard age puts the K/T boundary event back to 66 Ma from 65.5 Ma. The formerly 251.0 Ma mass extinction at the end of the Permian becomes 252.5 Ma, which coincides better with the outpouring of the Siberian Traps. Similarly, the once 200 Ma end-Triassic extinction, but now possibly 201.6 Ma, links better to the Central Atlantic Magmatic Province outpourings. Quite a stir may be on the horizon, if Kuiper and colleagues’ recalibration is confirmed by similar independent measures.

That radiocarbon dates need to be used with caution is well known, as the amount of 14C produced by cosmic ray bombardment of atmospheric nitrogen varies markedly over time. Again, the ‘work-around’ involves using non-radiometric ages to calibrate the fluctuating relationship between radiocarbon ages and real time. The data of choice are those from tree-ring analysis, but ice cores also preserve ages with a 1-year precision from their annual layering. The Younger Dryas cold period that interrupted the global deglaciation began when atmospheric 14C production was high. It was also a tremendously important event in the progress of human migration and perhaps even genetics – population crashes in hard times can have a ‘bottleneck’ effect on evolution. A multinational team has addressed the interrelations between radiocarbon dating, ice-core climate proxy records and tree-ring analysis for this crucial episode (Muscheler, R. et al. 2008. Tree rings and ice cores reveal calibration uncertainties during the Younger Dryas. Nature Geoscience, v. 1, p. 263-267). They combined measures of varying 14C in tree rings and 10Be in ice cores, both of which are cosmogenic. Rather than resolving the issue, they discovered that the best marine record of the carbon-cycle during the YD, in the Cariaco basin off Venezuela, has a bias caused by anomalous concentration of 14C in shallow seawater as the YD began. Their study open the possibility of resolving such changes in the marine C-cycle.

See also: Kerr, R.A. 2008. Two geological clocks finally keeping the same time. Science, v. 320, p.434-435.

Great surprise: Deccan flood volcanism emitted gases

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The only documented volcanic eruption resembling those thought to characterise effusion of flood basalts was of the Icelandic Laki fissure in 1783. At 14 km3 its lava volume was minuscule compared with those of ancient flood-basalt flows, but it did have a remarkable effect on the atmosphere and climate of the Northern Hemisphere. A bluish, ground-hugging dry fog spread over much of Europe and North America. The fog caused severe chest ailments and was probably full of sulfuric acid aerosols. Such droplets also serve to increase the reflectivity of the atmosphere, thereby reducing solar heating. In fact, witnesses remarked on how dim the summer sun appeared that year, although it seems not to be particularly chilly. The climatic effects emerged the following winter with the average temperature in Paris falling by almost 5°C from the long-term average. On Iceland itself, crops failed during the eruption, but worse was to come. Both livestock and humans developed the awful bone lesions associated with fluorosis, for the basalt magma emitted hydrogen fluoride as well as SO2. Human and animal skeletons from the time show gross bone deformities, often like fibrous needles that would have grown through living flesh. Gas emissions from modern basalt flows chemically similar to those of Laki and far larger flood basalts are well documented, and the potential climate effects of continental flood basalt magmatism have been modelled repeatedly using those data.

Measuring actual gas contents of the magmas that fed ancient lava flows is difficult, simply because most magma degasses before it finally crystallises. Even vesicles are devoid of pristine gas that formed them, due to later percolation of fluids. In a few extremely fresh flows some of the original magma may have been preserved as glassy blobs trapped within phenocrysts such as olivine or Ca-plagioclase that formed in magma chambers before eruption. A group from the Open University, UK has analysed sulfur and chlorine content in four such minute samples by electron probe and XRF, finding levels up to 1400 and 900 ppm respectively (Self, S. et al. 2008. Sulfur and chlorine in late Cretaceous Deccan Magmas and eruptive gas release. Science, v. 319, p. 1654-1657).  The sulfur values are not unusual compared with modern basaltic glasses that have not lost their magmatic gases, though chlorine concentrations are somewhat high in the known range.

The climatic and environmental implications of both gases are noteworthy, mainly because each basalt flood would have emitted hundreds to thousands of teragrams of each annually – vastly more than modern emissions by both humanity and active volcanoes. In the lower atmosphere effects would have been like those of Laki – locally choking fogs acid rain, and cooling. Had chlorine reached the stratosphere it would have destroyed ozone to increase exposure of terrestrial life to UV radiation. So quite a few large-scale kill mechanisms may be ascribed to continental flood basalts such as the Deccan province.

This may well be the first direct evidence for actual gas-emission potential of ancient basalt magma samples. Sadly, however, the specimens containing glass were erupted some time before the K-T extinction event – the on-line data supplement reports ages of 66-68 Ma for the lower Deccan flows in which glass inclusions occur, between 0.5 to 2.5 Ma earlier than the end of the Cretaceous. That undermines, to some extent, the need to have analysed the glasses in the first place, when modern data serve well for modelling the effects of CFBs.  Still, even at the low end of S and Cl contents of modern undegassed basalt magmas, the stupendous volume of any flood basalt province – up to millions of km3 – would have repeatedly placed great stresses on the biosphere. The wonder is that not all CFBs are associated with mass extinctions, so maybe the environmentally less-destructive CFB provinces since 250 Ma ago (8 out of 11) involved magmas with extremely low S and Cl contents…

Clovis First hypothesis dumped

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For decades palaeoanthropology of the Americas has been dominated by a single idea; that nobody entered the continents before those people who used the elegant fluted spear blades first found near Clovis, New Mexico in the 1930s. These were eventually dated at a maximum age of around 13 ka before the present. One reason for accepting the Clovis people as the first Americans, apart from the lack of conclusive evidence for any earlier occupation, was the fact that glaciers blocked the route from the Bering land bridge of the last Ice age until about 13 ka. Increasing evidence has suggested earlier penetration by people who did not use Clovis tools from Asia, which reached Chile by around the same time and possibly as early as 33 ka. However, none of the evidence is definitive and the Clovis First hypothesis has been stoutly defended against this growing body of contrary evidence.

The ‘traditional’ idea of American occupation by humans after 13ka has taken a double whammy from an unusual set of fossils – of human excrement – discovered in a cave in Oregon. These have been dated at up to 15 ka and are unmistakably human, containing human mtDNA with genetic signatures typical of Native Americans (Waters, M.R. & Stafford, T.W., Jr. 2007. Redefining the Age of Clovis: Implications for the Peopling of the Americas. Science v. 315, p. 1122-1126; Gilbert, M.T.P et al. 2008. DNA from pre-Clovis human coprolites in Oregon, North America. Science, DOI:10.1126/science.1154116).

Ideas of how and when the Americas were colonised are changing rapidly after decades of ossification. A fascinating article in the 14 March 2008 issue of Science magazine reviews the issues and prospects (Goebel, E. et al. 2008. The late Pleistocene dispersal of modern humans in the Americas. Science, v. 319, p. 1497-1502). Genetic studies of living native Americans suggest their common ancestry in a Siberian population no earlier than 30 ka, and perhaps as late as 22 ka. The Beringia land bridge had repeatedly created a possible migration route during every major glaciation followed by many of the Pleistocene mammals that inhabited the Americas, but not by humans until the late stages of the last glaciation. Dating of archaeological sites and remains, including the human coprolites found by Waters and Stafford, is slowly pushing back the earliest evidence for a human presence to around 15 ka, several trhosand years before the Clovis culture appeared. Sometime before that, the first Americans had arrived and begun to spread. Ice barred their way through the interior of Alaska and NW Canada, and they must therefore have travelled along the coast, where the way was open from Beringia to Cape Horn; perhaps they used boats to move along the flat, but frigid shores of Beringia and the rugged western seaboard of North America. Early populations subsisting on shoreline resources would not have needed the heavy projectiles of the Clovis culture that are more attuned to ‘big-game’ hunting on plains. That may explain the sudden appearance of Clovis artefacts once access to plains was possible around 13.5 ka and its equally sudden disappearance at the start of the Younger Dryas around 12.8 ka when survival on icy plains would have become very difficult. Interestingly, the period of occupation of Siberia around 30 ka, would have presented the Beringia route to migration to North America when climate was similar to that following the last glacial maximum. So far, no tangible evidence

Homo floresiensis had big feet

Controversy has raged about her identity since the skull of a minute female hominin was unearthed from the Liang Bua cave on the Indonesian island of Flores. On the one hand are authorities who believe the fossil is that of a distinct human species, while on the other are sceptics convinced that the diminutive stature and chimp-like brain capacity reflect some pathological issue in a population of ordinary humans. The 12 April meeting of the American Association of Physical Anthropology in Columbus, Ohio (see Culotta, E. 2008. When hobbits (slowly) walked the Earth. Science, v. 320, p. 433-435) were treated to an anatomical exposition of the rest of the Liang Bua skeleton. A great deal more turns out to be different from human characteristics, including the legs and feet. Amusingly, for J.R.R. Tolkien’s Hobbit had them, the feet of H. floresiensis were disproportionately large. Also, her gait was quite different from ours – a kind of careful, high-stepping plod. Although not all agree, the post-cranial bones of H. floresiensis appear to bear close resemblance to those of early Homo species. Those favouring a separate species from our own suggest either that it arose through allopatric speciation from SE Asian H. erectus  after isolation of a population on Flores, or perhaps even that it is a relic of an early migration of H. habilis from Africa almost 2 Ma ago. Whatever, it is now going to be even more difficult not to speak of hobbits.

Orrorin walked the walk

Orrorin tugenensis is one of those fossils over which palaeontologists tend get heated. It is a hominin, old (~6 Ma) and fragmentary, so it just might be the daddy of us all. That possibility takes a significant step forward with statistical evidence that Orrorin walked upright in a similar manner to the much later australopithecines and paranthropoids (Richmond, B.G. & Junggers, W.L. 2008. Orrorin tugenensis femoral morphology and the evolution of hominin bipedalism. Science, v, 319, p. 1662-1665). The study was made independently of the original discoverers, who claim that the femur has especially human-like features. Whichever, one of the original suggestions that Orrorin  was on the ancestral line to gorillas has become improbable. The creature clearly displays the oldest known example of a bipedal gait (the older Sahelanthropus (~7 Ma) is known only from skull fragments and teeth, although its skull’s foramen magnum hints at bipedalism). In itself, Orrorin’s walking biomechanics is remarkable, as molecular evidence suggests that the branching that led to chimpanzees and to hominins is not much older than 6 Ma. It does seem as if that phylogenetic split may well have centred first on adaptation for traversing open ground from a forest common ancestor.

Colonisation of Europe pushed further back

Europe is so close to Africa that in recent years repeated waves of immigrants have crossed the Straits of Gibraltar, often on frighteningly flimsy craft. Their driving force is simply the search for a better life in the booming economies of Spain and Italy. Far more intense pressure from deteriorating climate and vanishing game drove Africans of many earlier times to escape their home continent, reaching back almost 2 million years. So how come the European hominin record is so short? At last count it went to H. antecessor around 750 ka, albeit a species that was sufficiently adventurous to reach British shores (see Earliest tourism in Northern Europe in EPN of January 2006). The famous Sierra de Atapuerca cave systems in northern Spain have now yielded clear evidence of much earlier occupants from around 1.1 to 1.2 Ma ago in the form of a lower jaw fragment in association with tools and bones showing signs of butchery (Carbonell, E. and 29 others 2008. The first hominin of Europe. Nature, v. 452, p. 465-469). Provisionally, the person has been assigned to H. antecessor, and there are two possible interpretations: either (s)he was a new immigrant from Africa, or represents a new speciation in northern Spain from an earlier population of African colonists. The paper’s title may prove to be premature.

 

Clouds and large earthquakes

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The press announced in April that the USGS and other western US geoscience institutes had issues the first ever comprehensive earthquake forecast for California (see http://www.scec.org/ucerf/) , but it was cautiously phrased in terms of probabilities of destructive magnitudes (>6.7) over the next 30 years. That might be fine and dandy for administrators and civil engineers, but not so good for anyone who becomes a victim at the precise time this or that Californian fault ‘goes off’. People world-wide have rarely chosen where to live based on knowledge of geological risks; indeed most threatened communities have little choice, for many reasons. What would be useful is being warned that a devastating earthquake is definitely due where one lives, and it will happen sometime in the next few days or weeks. Even an hour’s warning will save many lives. But no geological survey will commit itself to that kind of pronouncement, except perhaps some of the many surveys in China. The fact that all kinds of phenomena, such as nervousness among animals, rising water levels in wells and so-on have been shown to occur shortly before many big earthquakes has prompted a kind of ‘barefoot’ monitoring that is officially co-ordinated in some parts of China. It is said that lives have been saved on a number or recent occasions.

It is easy for western scientists to make the analogy with homeopathy, and pooh-pooh such methodology. Also, there has been a succession of observations from space that could prove useful, such as ‘earth lights’ and magnetic-field fluctuations that accompany some seismic events (see Remote signs of earthquakes in EPN August 2003, Early warning of earthquakes in EPN December 2005). The latest odd, but conceivably useful connection is an association of unusual cloud formations with earthquakes in Iran (Guo, G. & Wang, B. 2008. Cloud anomaly before Iran earthquake. International Journal of Remote Sensing, v. 29, p. 1921-1928). The authors, from Nanyang Normal University in China, scrutinised free, hourly images from the geostationary Meteosat-5 satellite covering the whole of Iran, where seismicity is concentrated on a single large zone of deformation that trends NW-SE through the Zagros mountains. On several dates they found cloud formations parallel to the fault zone. Between 60 to 70 days later large eathquakes took place along the fault, including the highly destructive Bam earthquake of 26 December 2003. Indeed, a noticeable thermal anomaly in clouds directly above Bam occurred 5 days before the disaster.

How often do tsunamis occur?

Fortunately, truly destructive tsunamis on the scale of that of 26 December 2004 are rare events. So much so that nobody has a clear idea of their average frequency at different exposed shorelines; a vital statistic for risk analysis. Tsunamis produce high energy marine deposits, but unless they are preserved in accessible locations their incidence would be difficult to estimate, and they may be confused with tempestites generated by hurricanes. One characteristic of tsunamis is that they are waves that affect the entire ocean volume, unlike wind waves whose effects are restricted to a few tens to hundred of metres, which can create unique features. Canadian, US and Omani sedimentologists have examined a sediment deposited in Oman by a recorded tsunami generated by a large earthquake off Pakistan in 1945 and have discovered one such signature (Donato, S.V et al 2008. Identifying tsunami .deposits using bivalve shell taphonomy.  Geology, v. 36, p. 199-202). The deposit, a coquina rich in bivalve shells, contains an unusually high proportion of still-articulated shells, suggesting that living animals were ripped from the seabed and then flung into a lagoon. Along with oddities in fragmentation of other shells and the sheer size and extent of the coquina, this feature seems to be characteristic of tsunamites. Features in the Oman example closely match those in another on the eastern shore of the Mediterranean Sea in Israel.