Sunday, 23 October 2011

Major earthquake in Van Province, eastern Turkey. 23 October 2011.

Slightly after 1.40 pm on Sunday 23 October 2011 the Turkish province of Van was shaken by an earthquake with a magnitude of 7.2 on the Richter Scale which occurred at a depth of 20 km, 16 km to the northeast of the provincial capital, also called Van. This was followed by a number of aftershocks, some exceeding 5 on the Richter Scale. This appears to have caused a large number of fatalities; at the time of writing the recorded death-toll has passed 70 and is likely to continue to climb.
Map showing the location of the 23 October quake and its aftershocks. Larger squares represent larger shocks, the reddish square is the most recent (at the time of writing). From the United States Geological Survey.

As of 6.00 pm GMT casualties have been reported in the cities of Van and Ercis (closer to the Iranian border), but there are no reports from the surrounding countryside, or across the border in Iran. The Turkish Red Crescent has dispatched emergency relief to the region, but at present rescue attempts seem to comprise largely local people moving rubble by hand.

Local news report, from the scene of the quake.

Turkey is an extremely earthquake-prone country, as the boundary between the Arabian and Eurasian Plates passes through its eastern provinces (red line on the map above), creating tectonic disturbances as the Arabian Plate pushes northward into the Eurasian. This is causing the Anatolian Block (roughly Turkey, the Greek Islands and the Peloponnese) to rotate anti-clockwise, splitting away from the rest of Eurasia in the north, and subduct beneath (northward moving) Africa in the southeast.

Map showing the stresses upon and movement of the Anatolian Block.

This has lead to a history of devastating earthquakes in Turkey (and Greece & Iran), the most notable of which in recent years was 1999 earthquake on the North Anatolian Fault that killed over 17 000 people in and around the city of Izmit.

Sunday, 16 October 2011

Ongoing volcanic activity on El Hierro in the Canary Islands.

The island of El Hierro in the Canaries is the peak of a shield volcano (a volcanic mountain made up of layers of lava, with a wider, less cone-shaped, profile than the more notable stratovolcanoes) rising 1500 m above the sea. It is about 1.2 million years old, but has been relatively inactive during recorded history, with one observed eruption in 1793, and some lava flows dated to the 1600s. With no recorded history of large scale volcanic eruptions the island has developed as a popular tourist spot, and has a permanent population of over 10 000. Then in July this year (2011) El Hierro began to change.

The island of El Hierro.

From the start of July onwards seismologists began to record small earthquakes beneath El Hierro. These were minor, none larger than a 3 on the Richter Scale, but shallow, with an average depth of about 10 km, and as time went on they were becoming more frequent. This is something that volcanologists pay careful attention to, as it can be a sign of magma movements beneath a volcano, heralding a forthcoming eruption. This lead scientists from the Instituto Volcanologico de Canarias to place a network of GPS monitors around the island, to measure any movements. On 24 August they reported that the volcano had inflated by about 1 cm during the previous month.

By 3 September El Hierro was experiencing up to 250 minor tremors a day, with some of the quakes as shallow as 2 km. There was then a fall off in the number and intensity of quakes, lasting until the 27th, when the quakes abruptly resumed. The local government issued calls for calm, but closed schools on the island as well as the only significant road tunnel, Los Roquillos. On the 28th there were reports of rocks emerging from the Pico de Malpaso summit, though local authorities have denied this. People living close to the mountain were evacuated, but as a precaution against landslides. At about this point newspapers started to point out that there had been previous predictions that a major eruption in the Canaries could cause an Atlantic-wide tsunami. Authorities in the Canaries denied that there was any risk of this unless there was a submarine eruption on El Hierro, something thought highly unlikely.

On the 29th evacuees were allowed to return to their homes, as the area of seismic activity had moved offshore into the Las Calmas Sea, to the south of the island. This was thought to be caused by magma moving into a new chamber beneath the island, but was not seen as a cause for alarm, as only about 10% of magma movements result in an eruption at the surface. These quakes persisted for the next couple of weeks, waxing and waning in strength.

On 10 October 2011 a small submarine eruption in the Las Calmas Sea was reported, 5 km from La Restinga, the most southerly point on the island, at a depth of about 600 m. A significant number of dead fish were seen close to the sight. The next day the alert level for La Restinga was raised from yellow to red, and an emergency meeting was called at the village's football field, where the villagers were informed they were to be evacuated to the north of the island. A 4 nautical mile (7.4 km) shipping exclusion zone was also placed around the eruption.

On 12 October two new volcanic fissures were discovered, one at a depth of 750 m, 3.7 km from the shore and the other at a depth of 500 m, 2.8 km from the shore. These apparently turned the water around them green, and gave off a strong sulphurous smell. This combination of dead fish, water discolouration and odour was interpreted as indicating the vents were emitting gas rather than lava, and it was hoped that this might cause the pressure in the magma chamber to fall, decreasing earthquake activity and reducing the risk of a full-scale eruption.

Helicopter footage of one of the green patches.

A satellite image showing the extent of water discolouration to the south of El Hierro; to give a sense of scale El Hierro is about 25 km from east to west. Satellite Image courtesy of RapidEye.

On 15 October volcanic pumice (a volcanic rock with many gas filled pores) was observed floating on the surface of the sea, confirming that the eruptions were not confined to just gas. At this point some scientists began to talk about the possibility of a new island emerging to the south of El Hierro. A day later giant gas bubbles were observed reaching the surface of the sea close to the shore.

A giant gas bubble off the coast of El Hierro.

Throughout this period of eruptions there have been discussions of the possibility of a major tsunami originating from El Hierro. Scientists at the scene have repeatedly suggested that they feel this is a highly unlikely outcome, however this is largely based upon informed guesswork.

In 2001 Stephen Ward of the Institute of Geophysics and Planetary Physics at the University of California Santa Cruz and Simon Day of the Benfield Grieg Hazard Research Centre at the Department of Geological Sciences, University College London published a paper in the journal Geophysical Research Letters in which they speculated that a volcanic eruption on La Palma in the Canaries could provoke an Atlantic-wide tsunami with devastating consequences.

In October 2011 a team lead by Pablo Dávila Harris of the Department of Geology at the University of Leicester published a paper in the journal Geology discussing the likelyhood of a similar tsunami being caused by a volcanic eruption on Tenerife.

Ultimately we simply do not know the probability of an eruption on El Hierro, or many other Atlantic islands, causing a major tsunami. In the Pacific, where the dangers of a major tsunami are much more obvious, there is a well established tsunami warning centre, and a similar system is under construction for the Indian Ocean. The danger of a major tsunami in the Atlantic is clearly lower than in either of these other oceans, but should such an event occur it is likely to have devastating consequences, both economically and in human terms. While the costs of such a warning system are likely to be unattractive to governments in the current economic climate, a considerable amount of money has already been spent looking for extra-terrestrial objects with the potential to impact the Earth; a less likely scenario, and one which we would be less clear how to react to.

Wednesday, 12 October 2011

Reconstructing cloud cover for ancient Earth, with a view to spotting a new one.

Four the past four billion years or so the continents have ambled back and forth across the face of the Earth, sometimes forming up to form vast supercontinents such as Pangea or Rodinia, at other times going on their own ways. For much of the past five hundred million years these continents have been covered by vegetation.

Both of these have had profound effects upon the climate. The position of the continents effects the flow of the oceans, and therefore the atmosphere; for example the Pleistocene ice ages are believed to have started after a land bridge developed between North and South America, preventing the flow of water between the Atlantic and the Pacific, and diverting the Global Ocean Conveyer-belt through the waters surrounding Antarctica. Vegetation effects cloud cover by pumping water into the atmosphere via transpiration, the process by which plants suck up water from the ground via their roots then let it evaporate from their leaves, driving their circulatory systems.

This month Esther Sanromá and Enric Palle of the Instituto de Astrofísica de Canarias published a paper on the online arXiv database at Cornell University Library detailing the results of an attempt to accurately model the cloud cover of the Earth at various points in its history. The theory behind this is fairly simple; a model is created in which the surface of the Earth is divided up into a large number of cells, each of which has a weather patter, which can be influenced by conditions acting on the cell (heat received from the sun, the nature of the ground cover bellow etc.) as well as the weather in neighboring cells. The maps used were based upon those from Ron Blakey of Northern Arizona University's Department of Geology's Global Paleogeography Website.

Quite accurate models of the modern climate can be made in this fashion, but for ancient Earths the task was going to be harder. Accurate models require modeling vegetative ground cover to understand the effect this has on the climate; thus tropical rain forests, high latitude boreal forests and grasslands have to be treated differently. Unfortunately we don't have a good enough understanding of the vegetative cover over the geological timescale to make this possible. Instead Sanromá and Palle were forced to use a far simpler model of ground cover; either vegetated or desert with desert further divided by latitude.

This had clear limitations, but it was thought that if a reasonably accurate model of the modern Earth could be built up in this way, then it would be worth proceeding with the models of ancient climates. The modern Earth has a photometric variability of 3.29% and a mean albedo of 0.315 (that is to say on average 31.5% of the light that falls onto the Earth is reflected back into space, but that this average can vary by up to 3.29%). The computer simulation was able to create a model with cloud cover of 4.16% and an albedo of 0.325; not an exact match for our climate, but reasonably close.

Having thus calibrated the simulation Sanromá and Palle moved on the model the climate of the Late Cretaceous, 90 million years ago. At this time the ancient continent of Pangea had completely broken up, and the continents had yet to start to collide again, so that they remained as separate entities scattered around the globe. In addition the Late Cretaceous had a much warmer climate than today, so that it lacked ice caps. This lead to the creation of vast inland seas on most of the continents, further breaking up the Earth's land cover. Armed with this information Sanromá and Palle came up with a model which gave the Late Cretaceous Earth a photometric variability of 4.27% and an albedo of 0.331 - not greatly different from that of the modern Earth.
The Earth in the Late Cretaceous.

Next Sanromá and Palle built a model of the Earth in the Late Triassic, 230 million years ago. At this time the world's land masses were joined into a single supercontinent, Pangea, that reached almost from pole to pole. In the Late Triassic this supercontinent was starting to break up, the plates in the east had separated giving Pangea a 'C' shape, and forming a knew ocean, the Tethys. The Triassic had a hot, dry, climate with no glaciation at either pole. Sanromá and Palle's model of the Triassic gave a photometric variability of 5.02% and an albedo of 0.327; still comparable to that of today.

The Earth in the Late Triassic.

After the Triassic Sanromá and Palle moved on to the Mississippian (Early Carboniferous), 340 million years ago. During this period the continent of Pangea was coming together, though the continents were still largely separate. The climate was warmer that today, with inland seas on many continents, but there was still glaciation at the South Pole. The period is noted for extensive forests that covered much of the land masses. The model that Sanromá and Palle constructed of the period has a photometric variability of 4.46 and an albedo of 0.329; again not greatly dissimilar to today.

The Earth in the Mississippian.

Finally Sanromá and Palle constructed a model of the Late Cambrian, 500 million years ago. During the Cambrian a global supercontinent, Pannotia, had started to break up, with three island continents, Laurentia, Baltica and Siberia (roughly analogous to North America, Europe and Asia) and a residual Supercontinent, Gondwana, mad up of the remaining continental plates. The Cambrian had a warm climate, but with some glaciation at the poles. Most importantly, the Cambrian was before the evolution of vascular plants. It is thought that algae, fungi and lichens colonized the land some time before vascular plants, though it is unclear how early. For the sake of the model Sanromá and Palle assumed the Earth's land masses to be lacking vegetation of any sort during the Late Cambrian; this may not be completely accurate, but it is clear that at some point the Earth's landmasses did lack vegetation, so this model has some use. This model produced an albedo of 0.351, not greatly different to that of later periods, but a photometric variability of 12.2% which is distinctive.

The Earth during the Late Cambrian.

It is predicted that within the next few years we will have the technology to detect Earth-sized planets orbiting other stars, and therefore potentially to detect other planets with the capability to support life. However an Earth-like planet supporting life is not necessarily a familiar place; the Earth had unicellular life (bacteria, algae etc.) in its oceans for billions of years before the emergence of multicellular forms such as animals and plants, and after these emerged it took time for them to colonize the land. Sanromá and Palle's models suggest that it would be possible for a telescope to tell the difference between an Earth-like planet with plant cover and one without, on the basis of its photometric variability.

See also The Kepler-18 planetary system, Just how big is Iota Draconis b? The End of the Cretaceous and Exoplantes on Sciency Thoughts YouTube.

Saturday, 8 October 2011

Dinosaur footprints discovered in Southwest Arkansas. October 2011.

This week scientists at the University of Arkansas revealed that they have discovered and been studying a large area of dinosaur footprints in the southwest of the state. They have not revealed the exact location as people have a nasty habit of digging up dinosaur footprints and selling them to private collectors, which destroys them as a resource for scientists; even if they can be recovered they are far less useful when out of position. The research is being lead by Stephen Boss of the Department of Geosciences at the William J. Fulbright College of Arts and Sciences and is funded by the National Science Foundation.

Some of the dinosaur footprints.

The prints so far exposed cover an area of over 10 000 m³, and date from the early Cretaceous between 115 and 120 million years ago. There are a large number of prints, which is slightly surprising as they were made in fairly hostile conditions, salt pans around a drying sea or lagoon, similar to those seen in the modern Persian Gulf. At first this seems slightly puzzling, but it is unlikely that the prints were all laid down at the same time; the field may well be showing accumulated trails built up over hundreds or even thousands of years.

A modern salt pan - few animals choose to spend much time here.

It is not considered possible to identify dinosaurs from their footprints alone, however in some cases it is possible to make an informed guess. The track field includes prints from both large therapod and sauropod dinosaurs, and there are unlikely to have been many different candidates for producing these.

A single large therapod dinosaur is well known from the Early Cretaceous of the Southwest United States, and analogy with modern ecosystems suggests that such an animal would have been unlikely to tolerate many rivals. This is Acrocanthosaurus atokensis, an 11 m allosauroid with a distinctive crest, thought to have weighed between 6000 and 7000 kg. Several sets of trackways in Texas have already been attributed to Acrocanthosaurus.

An artists impression of Acrocanthosaurus atokensis, by restoration artist Mineo Shiraishi.

There are two known sauropod dinosaurs from the region during the Early Cretaceous, and again this is likely to be the limit. No modern environment supports two species of elephants, and only one (the savanahs of eastern and southern Africa) two species of rhino. Thus it is likely that the sauropod prints belong to one or both of these dinosaur species. These are Plueurocoelus nana and Paluxysaurus jonesi two similar 15 m brachiosaur-like dinosaurs, which are the former and current official state dinosaurs of Texas respectively. The similarity, both in anatomy and distribution of these dinosaurs makes them hard to tell apart, though in certain features they are distinctive; it is possible that they represent an example of sexual dimophism in a dinosaur. It is also possible that Astrodon johnstoni, a similar dinosaur from the Early Cretaceous of the northwestern United States.

As well as making plaster casts of the footprints which can be taken back to the lab, the team have been making detailed 3D laser scanned images of the whole site, this not only gives an accurate three dimensional images of the footprints within a computer, it also maps the prints on the ground accurately enabling scientists to study the foot-spacing and therefore gait of the printmakers. Footprints do not always accurately represent the foot-shape of the printmaker. In muddy terrains footprints are often distorted by the viscosity of the mud, but on this sort of terrain this is less likely. More likely is that the prints are in fact underprints; when an animal steps on a layered terrain it crerates prints not just at the surface, but in the layers beneath, as sediments are pressed down through one-another. These underprints are often preserved while the overprints are destroyed at the surface, but they are less accurate representations of the footprint maker.

How underprints are formed, different prints from the same foot, and how tracks are measured.

Friday, 7 October 2011

Could we mine the moon for titanium?

This week scientists at the joint meeting of the European Planetary Science Congress and the American Astronomical Society's Division of Planetary Sciences in Nantes, revealed the discovery of extensive titanium reserves of the moon, with widespread deposits of the mineral ilmenite containing up to 10% titanium; ilmenite on Earth typically contains only 1% titanium. The research was presented by Mark Robinson of Arizona State University and Brett Denevi of Johns Hopkins University in Baltimore. It was based upon findings made by NASA's Lunar Reconnaissance Orbiter; which was able to make a spectrographic analysis of rocks on the lunar surface, by calibrating the spectral signal to rocks brought back from the surface by the Apollo 17 Astronauts and images made of the landing site by the Hubble Space Telescope.

A Lunar Reconnaissance Orbiter image of the moon.

This has lead to widespread speculation that we might mine titanium on the moon. Titanium is a valuable metal, lightweight, strong and corrosion resistant. It used in surgical implants, aircraft and high technology. The lunar reserves have been shown to be much richer than those on Earth, and in a form that is also rich in oxygen, something that any lunar colony would require.

However while titanium is valuable, this does not mean that it is automatically valuable enough to justify the expense of a lunar colony. Titanium is the ninth most abundant element on Earth, and the seventh most abundant metal. We extract about 90 000 tonnes of the metal from the Earth's surface, but there are thought to be workable reserves of about 600 000 000 tonnes; that is to say at current rates of extraction reserves will last for another 666 years, assuming no increase in recycling, nor any better replacement material being found. Resources that were valuable in 1345 are not necessarily the same ones considered valuable now; Europeans never hailed the discovery of America as a potential source of cheap thatch for their roofs. As such it is probable that any successful future lunar colony might choose to mine titanium for its own use, but highly unlikely that one would ever be established for the express purpose of titanium mining.

Thursday, 6 October 2011

The Kepler-18 planetary system.

This week NASA announced the discovery of a planetary system by the Kepler Space Telescope. This has been named Kepler-18; it was formerly identified as KIC 8644288 (where KIC is Kepler Input Catalogue, a catalogue of all the stars in the Kepler field of vision). The system has a single star, which is similar to our sun; it has 97% of the sun's mass, and a volume of 110% that of the sun, it's surface temperature is slightly cooler.

The system has three (known) planets, named Kepler-19b (closest to the star), Kepler-18c and Kepler-18d. Kepler-19b is a rocky planet, 3.4 times the size of the Earth, Kepler-18c and Kepler-18d are larger, Neptune-like worlds, six and seven times the size of the earth respectively. Both these planets are less massive than Neptune, but have slightly larger volumes, suggesting they have larger gaseous envelopes and smaller rocky cores.

All three planets orbit within the orbital radius or Mercury (it is likely that there are other planets further out and harder to detect). Kepler-18b has a year of only 3.5 of our days. Kepler-18c and Kepler-18d are locked in an orbital resonance with orbits of roughly 7.6 and 14.9 (Earth) days respectively. The orbital resonance is caused by an exchange of orbital momentum between the planets as they pass each other; this also means the orbits are not quite constant. At any given time one of these planets will be running ahead of its average orbit and the other behind. Each time they pass they exchange energy, so that the one that was running slow speeds up, and the one that was running fast slows down.

A diagrammatic representation of the Kepler-18 system comparing the sizes of the star, planets and planetary orbits to those of our solar system.

The discovery was announced this week at a joint meeting of the American Astronomical Society's Division of Planetary Science and the European Planetary Science Conference and published in a paper on the on-line arXiv archive at Cornell University Library, by a team led by William Cochran of the McDonald Observatory at the University of Texas, and is scheduled for publication in the Astrophysical Journal Suplement Series.

Following initial identification of the system with the Kepler Space Telescope the team made follow up observations with the Shane and Nickel Telescopes at the Lick Observatory, the United Kingdom Infrared Telescope, the Wisconsin-Indiana-Yale National Optical Astronomy Observatory, the Hale Telescope at the Palomar Observatory, the Keck 1 HIRES spectrometer and the Spitzer Space Telescope. This enabled the scientists not only to build up a more complete picture of the Kepler-18 system, but also to confirm that the dimming of the star due to planets passing in front of it (how the system was detected) did indeed occur at a checkable electromagnetic wavelengths, considered a good way to determine that this has been caused by a planet and not some other phenomenon.

Earthquake in Jujuy Province, NW Argentina. 6 September 2011

Sightly before 8.15 am on Thursday 6 September 2011 the Jujuy Province in the far northwest of Argentina was shaken by a severe earthquake, recorded by the United States Geological Survey as having a magnitude of 6.8 on the Richter Scale and a depth of 9.5 km; this is shallow enough that it is likely to have caused severe problems at the surface, although it is in a rural area with a fairly sparse population, with only 819 people living within 20 km of the epicenter, so it is hoped that there have been no fatalities. The nearest settlement to the epicenter of any size is San Pedro, 62 km to the east, with a population of about 75 000.

The location of the quake.

The province has a largely rural economy, however it is also home to an extensive mining industry, which may have placed more people at risk. The earthquake was felt across the province and in the neighboring provinces of Salta, Tucumán, Catamarca and Santiago del Estero, as well as in southern Bolivia. Public buildings in Jujuy and Tucumán were evacuated, and there have been reports of damage to buildings in Jujuy and Salta. The situation close to the epicenter is as yet unclear.

Jujuy is located in the Andes Mountains, one of the most tectonically active mountain ranges in the world, and has a history of earthquakes. The Andes are being formed as the Nazca Plate to the west is subducted beneath the South American Plate. This causes quakes in a number of ways. Firstly there is friction between the two plates as the Nazca Plate passes under South America. Then there is crumpling and upthrust of the South American as it is pushed from the west by the Nazca Plate and from the east by the expansion of the Atlantic. Finally there is volcanic activity in the Andes, as lighter minerals in the Nazca Plate are melted by the heat of the Earth's interior, then rise up through the overlying South American Plate to form volcanoes.

Diagram showing how the the subduction of the Nazca Plate deforms South America, forming the Andes.

In February 2010 an earthquake with a magnitude of 6.3 on the Richter Scale in the neighboring province of Salta killed two people, and on the same day an unrelated earthquake killed 500 people in Chile. Both the victims, an eight year old boy and a fifty-three year old man, were killed in house collapses. The Chilean earthquake on the same day measures 8.8 on the Richter Scale, the fourth largest earthquake ever recorded (the strongest earthquake ever recorded also hit Chile, in 1960) and caused a tsunami that hit California and Japan.

Tuesday, 4 October 2011

Eruptions on Mount Nabro, Eritrea.

Mount Nabro is a stratovolcano (a cone-shaped volcano of the kind seen in Hollywood movies, made up of successive layers of ash an lava) in the southeast Danakil Desert in Eritrea, close to the Ethiopian border. It forms part of the Bidu Volcanic Complex, along with the Dubbi and Sork Ale volcanoes in Eritrea and Mallahle and Bara Ale volcanoes in Ethiopia. Until this year there have been no recorded eruptions at Nabro, and it had been assumed to be extinct, though due to its remote location it had not been studied extensively.

Satellite image of Mount Nabro.

On 12 June 2011 the area around Mount Nabro was shaken be a series of earthquakes, which rose in intensity throughout the day. At approximately 9 pm local time on 13 June a large volcanic eruption took place in the region, creating a column of ash that rose 13.5 km into the air. At first this was thought to have been caused by an explosion on Mount Dubbi, the only volcano in the area to have erupted in recorded history (in 1861), causing concerns for the settlement of Afambo, which is close to Dubbi, but Nabro was later identified as the source of the eruption from satellite photographs. Within hours the ash column had started to cause disruption to flights in the region.

Satellite image of the eruption on Mount Nabro.

On 16 June the Eritrean Government announced an evacuation of the people of Afambo, Nebro and Sireru, the three settlements closest to the eruption.

By the end of June the ash cloud had cleared sufficiently for NASA to obtain pictures of the situation on the ground, revealing that a large amount of lava had issued from the caldera of the volcano, producing a flow of lava that extended westwards for over 12 km before producing a lava lake. It was also becoming apparent by this point that the evacuation by the Eritrean Government had not been entirely successful and that seven people in Eritrea had lost their lives as a result of the eruption, and a further three had been injured.

Satellite image of the lava flows from Mount Nabro.

A week later the neighboring Ethiopian state of Afar reveled that at least 31 people had died their, and that the local government was having extreme difficulty coping with deteriorating environmental conditions associated with the eruption, particularly water pollution and damage to crops and livestock. The Afar Government estimated that 48 000 people were in immediate danger from the ash-fall and that over 167 000 more were potentially at risk. Clouds of poisonous sulphur dioxide gas were also reported to be blowing across the border. It launched an appeal for aid, but this was overruled by the Federal Ethiopian Government in Addis Ababa.

On 9 September 2011 the area began to experience seismic activity again with small earthquakes persisting for the next three days. On 28 September NASA again reported sighting fresh lava flows on Mount Nabro.

The Bidu Volcanic Complex is located on the Afar Triple Junction, a complex area tectonically, where three spreading plate margins meet. To the northwest the Red Sea Rift runs between Africa and the Arabian Peninsula, a new ocean ridge where oceanic crust is being formed, with the potential to turn the Red Sea into an ocean over the next few million years. To the northeast the Aden Ridge forms a similar divergent margin between the Arabian Peninsula and the Indian Ocean, although in this case both plates are moving northward, the Arabian Peninsula is simply moving faster than the Indian Ocean for the time being. It is likely that as Arabia collides with Eurasia it will slow down and the Indian Ocean will overtake it, closing the Aden Rift. To the south the Great Rift Valley is slowly splitting Africa in two, creating a long chain of volcanoes heading south to Mozambique. Some geologists believe that a mantle plume beneath the Afar Triangle is fueling this, pushing the plates apart rather than their being drawn apart by seismic activity elsewhere.
The hypothetical Afar Plume.

Monday, 3 October 2011

A re-evaluation of the Iwo Eleru skull.

Iwo Eleru is an archaeological site in southeast Nigeria, which comprised a rock shelter containing a number of stone tools and a single human skeleton. It was excavated in 1965 by a team lead by Thorstan Shaw of the University of Ibadan. The findings were published in 1971 in a paper in the journal Man (since 1995 replaced by The Journal of the Royal Anthropological Institute) by Don Brothwell of the Natural History Museum and Shaw. The initial study made morphometric analysis of the skull which suggested that Iwo Eleru man was similar to modern West Africans, but with some archaic features. Morphometric analysis is a method by which a large number of measurements are taken of a fossil, then compared to similar fossils within the same group in order to determine affinities. A radio-carbon date was established for charcoal associated with the skeleton, which gave a age of approximately 13 000 years.

The location of Iwo Eleru and the reconstructed skull.

This month a team lead by Katerina Harvati of the Senckenberg Center for Human Evolution and Paleoecology, Eberhard Karls Universität Tübingen published a paper in the journal PLoS One in which they re-examine the Iwo Eleru skull and provide a new morphometric analysis based upon digital measurements of the skull (the original study used calipers, the best technology available at the time) and a uranium-thorium date for the site.

Despite the extensive studies that have been made of the origins of humanity in Africa, comparatively little is known about human populations there during the Late Pleistocene, and even less for West Africa. For the purpose of the study the Iwo Eleru skull has been compared to a number of neanderthal, Homo heidelbergensis, Homo erectus, modern and other Pleistocene African and Near Eastern skulls. The other African and Near Eastern Pleistocene skulls were the two skulls from Jebel Irhoud in Morocco, currently dated at 160 000 years old, the Ngaloba skull from Laetoli in Tanzania, currently dated at 120 000 years old, two skulls from Qafzeh in Israel, currently dated at between 80 000 and 120 000 years old, the Singa skull from Jebel Irhoud in eastern Sudan, currently dated at between 87 000 and 127 000 and the Skhul skull from Mount Carmel in Israel, currently dated at 100 000 years old.

The morphometric analysis produced by Harvati et al. produced to distinct groups of skulls, one containing the archaic humans (neanderthals, Homo heidelbergensis, Homo erectus) and one containing the modern humans, with some of the Pleistocene African and Near Eastern skulls falling into these groups and some intermediate.

One of the Qafzeh skulls fell consistently within the archaic group, and the Skhul skull was consistently either in or close to this group (more than one analysis was run, since none of these skulls is complete). The other skulls were, depending on the analysis, either in or close to the modern set, or intermediate between the two - with the exception of Iwo Eleru, which was consistently intermediate between the two groups.

This suggests that Iwo Eleru is not a fully modern human, and that therefore more archaic humans can be thought to have persisted in West Africa later than was previously thought. However Harvati et al. do not consider Iwo Eleru to be distinctive enough to classify it as a separate species, preferring to consider it to be an archaic form of modern human (Homo sapiens).

Until comparatively recently the idea of archaic humans surviving as recently as the Late Pleistocene would have been highly controversial. However the recent discoveries of Homo floresiensis in 2003, a distinct species of humans that survived as recently as 13 000 years ago on Flores Island in Indonesia and the Denisovan people in 2010, a species of human living in Siberia around 40 000 years ago, make this rather less surprising. Instead this extends our knowledge of archaic human forms that lived alongside us until quite recently into a new area.

The skull of Homo floresiensis, a 1.1 m hominid from Indonesia.

The Uranium-thorium date established for the bones gave an age of between 11 700 and 16 300 years old, consistent with the original dating.

Sunday, 2 October 2011

A Sei Whale stranded in the Humber Estuary.

On Wednesday this week (28 September 2011) a young Sei Whale, 10 m long, was reported stranded in a salt marsh on the north side of the Humber Estuary (erroneously reported as a 'field' in some newspapers), near the village of Skeffling. It apparently became trapped while feeding close to the shore during a high equinox tide, then rolled onto its side as the waters retreated, covering its blowhole and dying of asphyxiation.

The stranded Sei Whale.

Sei Whales (Balaenoptera borealis) can reach 20 m long and weigh up to 28 tonnes. They are baleen whales feeding largely on copepods and other small crustaceans. They are fast swimming whales at home in the open water and usually avoid enclosed areas. This means that strandings are rare but when they do become trapped they have little chance of survival. This is the third Sei Whale stranded in UK water in the last 20 years, and 14th in the last one hundred. Following large scale hunting in the nineteenth and twentieth centuries they were driven close to extinction, but numbers have started to recover and the global population is currently thought to be about 80 000; they are still classified as endangered. Experts view individual strandings as sad, but as an indication of recovering stocks, not altogether a bad thing (more strandings will occur when there are more whales).

A Sei Whale as it appears when alive.

According to the Yorkshire Wildlife Trust whale strandings are becoming increasingly common on the Humber Estuary and Northeast English Coast. Whales seem to be particularly vulnerable in the estuary due to its extreme tidal range (7 m).

On 6 September this year a young Fin Whale (Balaenoptera physalus) became stranded in mud on the Lincolnshire side of the estuary, near Immingham Docks. This was dug out and refloated (with some difficulty) by volunteers from the Sea Watch Foundation, Cleethorpes RNLI, Humber Rescue, Lincolnshire Fire and Rescue, the RSPCA, the Coastguard and British Divers Marine Life Rescue, but unfortunately re-stranded and died near Cleethorpes two days later. Like Sei Whales, Fin Whales are a large (up to 27 m), fast swimming, deepwater species that where formerly heavily hunted. Strandings are rare, but again considered a sign of recovering populations. The global Fin Whale population is currently thought to be somewhere between 100 000 and 119 000 individuals.

Volunteers digging out the stranded Fin Whale, earlier this month.

In November 2007 a dead whale was seen floating in the Humber near Alexander Dock, but washed out to sea before experts could determine what species it was. In 2006 a Humpback (Megaptera novaeangliae) became trapped in a ferry port on the river and died and a Sperm Whale (Physeter macrocephalus) was found dead at Spurn Point on the estuary.

A Humpback Whale was stranded and died at Gravesend on the Themes Estuary in 2009. In 2007 a Humpback was stranded at Carnoustie in Angus, Scotland. This was refloated but a day later a whale tangled in fishnets was recovered at Arbroath, which is thought to have been the same animal. In 2006 a Humpback whale was found dead at Lombardsijde in Belgium, having apparently been hit on the head by a ship's propellor.

The Gravesend Humpback.

A Sperm Whale was also stranded on a beach near Redcar in Cleveland in June this year, and died despite attempts to refloat it. In 2006 two Sperm Whales, a male and a female, were stranded at Skegness, to the south of the Humber Estuary. The female was found dead, but volunteers managed to refloat the male. Unfortunately the male was washed up dead the next morning. In 2004 a Sperm Whale became stranded on a sandbank at Sutton Bridge in the Wash and died despite efforts to refloat it. Another dead Sperm Whale was found at Thornham in Norfolk in 2004. This was washed out to sea, and came ashore at Koksijde in Belgium. later Sperm whales were also reported stranded in Holland in 1995, Belgium in 1994 and Denmark in 1991.

In September 2009 a Fin Whale was found dead in Antwerp Harbour in Belgium, apparently having been hit by a ship.

In March 2008 a Cuvier's Beaked Whale (Ziphius cavirostris)was found dead in the Moray Firth in Scotland; this species has been recorded stranded in Ireland and on the Atlantic Coast of Scotland, but this was the first recorded instance of one in the North Sea.

In January 2006 a female Northern Bottlenose Whale (Hyperoodon ampullatus) became trapped in the River Thames, and died despite attempts to rescue it.

The Bottlenose Whale passes the Houses of Parliament in London.

The commonest whale in the North Sea is the Minke (Balaenoptera acutorostrata) but these are seldom stranded, being well adapted to inshore conditions and shallow, tidal waters. Strandings of whales are often blamed on both Naval Sonar and the activities of North Sea oil drillers, but if this is the case it is difficult to explain the apparent immunity of Minke Whales to these disturbances.

Whale strandings in the UK can be reported on the Natural History Museum's website here.
Whale sightings can be reported to the Sea Watch Foundation here.

See also Mammals on Sciency Thoughts YouTube.