Sciency Thoughts: February 2015

Saturday, 28 February 2015

Magnitude 3.0 Earthquake off the southwest coast of Jersey.

The British Geological Survey recorded a Magnitude 3.0 Earthquake at a depth of 10 km, roughly 22 km to the southwest of the island of Jersey in the Channel Islands at about 10.55 pm GMT on Wednesday 25 February 2015. Although large for the area, the quake was still to small to present any threat to human activity, and there were no reports of any damage or injuries relating to this event, though it was reportedly felt on the island.

The approximate location of the 25 February 2015 Jersey Earthquake. Google Maps.

The precise cause of Earthquakes around the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process.

Simplified diagram showing principle of glacial rebound. Wikipedia.

Glacial rebound seems an unlikely cause of Earthquakes beneath the Channel Islands, an area that was never glaciated, but this is not entirely the case. The northwest of Scotland is rising up faster than any other part of the UK, but the Earth's crust onland in the UK is fairly thick, and does not bend particularly freely, whereas the crust beneath the Channel is comparatively thin and more inclined to bend under stress. Thus uplift in Scotland can cause the entire landmass of Great Britain to pivot, causing movement in the rocks beneath the Channel.

Map showing areas of the British Isles currently rising or sinking as a result of glacial rebound. Wikipedia.

Witness accounts of Earthquakes can be useful to geologists trying to understand the processes that cause them and the rocks beneath the surface. If you felt this quake (or if you were in the area but did not feel the quake, which is also useful information) then you can report it to the British Geological Survey here.

See also...

Magnitude 1.9 Earthquake southwest of Jersey in the Channel Islands.

The British Geological Survey recorded a Magnitude 1.9 Earthquake at a depth of 6 km, roughly 15 km to the southwest of the island of Jersey in the Channel...

Magnitude 1.8 Earthquake beneath the island of Jersey.

The British Geological Survey recorded a Magnitude 1.8 Earthquake at a depth of 7 km beneath the eastern part of the island of Jersey in the Channel Islands...

Magnitude 2.9 Earthquake in northern France.

A Magnitude 2.9 Earthquake at a depth of 10 km occurred beneath the commune of Miniac-Morvan, near St Malo in Brittany, northern France, slightly after 11.35 pm local time (slightly after 9.35 pm, GMT) on Wednesday 3 July 2013, according to the Laboratoire de Détection et de Géophysique. There are no...

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Two new species of Vampire Crabs from Central Java.

Sesarmid crabs of the genus Geosesarma are large, often colourful, fully terrestrial Crabs found in Southeast Asia and Indonesia. In recent years they have been traded in the international aquarium trade under the name ‘Vampire Crabs’ (which is fanciful, the Crabs do not drink blood but feed largely on small Insects etc.), with several species unknown to science appearing in the aquarium trade. The origin of these has been hard to track down, with dealers claiming they originate from Sulawesi, Java, Krakatau (highly unlikely since Krakatau is an active volcanic island with no fresh water supply, which has been completely resettled by wildlife from outside following the destruction of the island by a violent eruption in the late nineteenth century, and its subsequent re-appearance) or the Riau Islands.

In a paper published in the Raffles Bulletin of Zoology on 16 January 2015 Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore, Christoph Schubart of Zoology and Evolutionary Biology at Universität Regensburg and Christian Lukhaup of Bittenfeld in Germany describe two new species of Vampire Crabs from Central Java, both of which have previously been encountered in the aquarium trade.

The first new specie described is named Geosesarma dennerle, in honour of the German company Dennerle, who supported Christian Lukhaup’s studies in Java. The Crabs have squarish bodies, a little wider than long, with the largest male located having a carapace 14.4 by 14.0 mm and the largest female 13.5 by 11.8 mm. They have a very distinctive colouration, with the front half of the carapace and legs being violet or purple and the rear of the carapace being cream or yellowish white. The crabs were found living on the slopes of a small valley, between rocks and in dense vegetation. The species has also been found being traded in Germany under the names ‘Vampir Vampirkrabbe’ and ‘Blaue Vampirkrabbe’.

Specimens of Geosesarma dennerle from Cilacap on Java. Christian Lukhaup in Ng et al. (2015).

The second new species described is named Geosesarma hagen, in honour of the Rolf C. Hagen Group of Companies, who are a major pet supplies group in Germany, and who supported both Christian Lukhaup’s studies in Java and subsequent work on the Crabs by Christoph Schubart. These Crabs are also squarish and wider than they are long; the largest male found had a carapace 13.9 by 13.3 mm, while the largest female was 14.5 by 13.4 mm. This species also has very distinctive colouration, with the front of the carapace and walking legs being brown while the rear of the carapace and claws are bright orange or yellow. This species has been traded in Germany as ‘Rot Vampirkrabbe’. The Crabs were found living in a Banana and Rubber plantation on the side of a small hill, about 300 m from a road.

Specimen of Geosesarma hagen from Cilacap on Java. Christian Lukhaup in Ng et al. (2015).

Ng et al. also note that both species are apparently being heavily collected for the aquarium trade, and that local people report that they have become scarcer in recent years. This strongly implies that they are being collected in an unsustainable way, and that if this persists it will be necessary to develop a conservation management plan for these Crabs, probably involving a captive breeding program. They also note that the conservation status of land Crabs as a group has not yet been assessed under the guidelines of the International Union for the Conservation of Nature’s Red List of Threatened Species, and that this needs to be done in the near future, particularly if their popularity in the aquarium trade persists.

Friday, 27 February 2015

Asteroid 2015 CA40 passes the Earth.

Asteroid 2015 CA40 passed by the Earth at a distance of 2 419 000 km (6.32 times the average distance between the Earth and the Moon, or 1.6% of the average distance between the Earth and the Sun), slightly before 9.50 pm GMT on Monday 23 February 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 CA40 has an estimated equivalent diameter of 21-73 m (i.e. it is estimated that a spherical object with the same volume would be 21-73 m in diameter), and an object of this size would be expected to break up in the atmosphere between 21 and 3 km above the ground, with only fragmentary material reaching the Earth's surface, although since an object at the upper end of this range would be expected to release an amount of energy equivalent to about 15 megatons of TNT (roughly 1000 times the energy released by the Hiroshima bomb), then being directly underneath it might be fairly unpleasant.

2015 CA40 in the morning of 24 Feb 2015 near 9 UT, some 12 hours after closest approach. Images taken overr a 10-minute timespan at 2 minute intervals and 30 second exposure. My Asteroid Discoveries/Sierra Stars Observatory Network.

2015 CA40 was discovered on 15 February 2015 (eight days before its closest approach to the Earth) by the University of Szeged's Konkoly Observatory in Hungary. The designation 2015 CA40 implies that it was the 1001st asteroid (asteroid A40) discovered in the first half of February 2015 (period 2015 C).

One of the discovery images of 2015 CA40. Marco Langbroek/My Asteroid Discoveries/Konkoly Observatory.

While 2015 CA40 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 424 day orbit, at an angle of 15° to the plane of the Solar System, that takes it from 1.004 AU from the Sun (1.004 times the average distance at which the Earth orbits the Sun), slightly outside our orbit, to 1.20 AU from the Sun, (1.20 times the distance at which the Earth orbits the Sun). As a Near Earth Object that remains strictly outside the orbit of the Earth it is classed as an Amor Family Asteroid. This orbit also means that close encounters between 2015 CA40 and the Earth are extremely common, with the last having occured in March 2008 and the next predicted for February 2022.

The calculated orbit of 2015 CA40. JPL Small Body Database.

See also...

Asteroid 2014 EK24 passes the Earth.

Asteroid 2015 DU passes the Earth.

Asteroid 2015 DU passed by the Earth at a distance of 3 068 000 km (7.97 times the average distance between the Earth and the Moon, or 2% of the average distance between the Earth and the Sun), at about 10.00 am GMT on Monday 23 February 2015...

Asteroid 2014 YM9 passes the Earth. Asteroid 2014 YM9 passed by the Earth at a distance of 15 510 000 km (40.35 times the average distance between the Earth and the Moon, or 10.4 % of the average distance between the Earth and the Sun), slightly after 11.10 pm GMT on Thursday 12 February...

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Three killed by Sumatra landslide.

Three people have reportedly been killed and another three seriously injured following a landslide at the village of Tambang Tinggi in the Sorolangun District of Jambi Province on Sumatra, on the evening of Thursday 26 February 2015. The three deceased have been named as Mariam, Desi and Tanto, while the injured have been named as Inam, Zainab and Raimah. The incident took place following sustained heavy rains in the area; landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

The approximate location of the 26 February 2015 Tambang Tinggi landslide. Google Maps.

Jambi Province has a wet tropical climate, with 2000-300 mm of rain per year and a wet season that lasts from October to March, with peak rainfall in January. Landslides are a common problem, particularly as a rising population is leading both to increasing deforestation (which removes tree roots that can stabilize slopes) and more people settling on or close to slopes where they are vulnerable.

The Tambang Tingii landslide has been linked by the Jambi Provincial Police to illegal mining in the area. Unlicensed artisanal mining is common on Sumatra, where many areas have deposits of alluvial gold (gold which has been eroded out of rocks elsewhere and deposited by rivers in places where the river slows - often at higher concentrations than it would have been found at in the original ore-rocks). The practice has widely been linked to increased erosion, flooding and landslide events, partly because of the associated deforestation (removal of trees which help stabilize soil in order to get at underlying deposits) and also because many miners excavate into river banks, where the highest concentrations of gold are found, leading to weakened banks and often changing the course of rivers. Attempts by local authorities to clamp down on such activities are often hampered by a perception that restrictions favour foreign mining companies, which do not always have a good reputation for environmental management or their treatment of local people.

See also...

Three feared dead after West Sumatra landslide.

Three people are missing presumed dead after a landslide struck a house in the village of Bukit Panjuik...

Landslide kills nine on northern Sumatra.

Nine people are confirmed to have died following a landslide in the Berastagi sub-district on northern Sumatra on Saturday 30 November 2013. Four of the dead are said to be children under 10 years old. The incident happened following several hours of heavy...

Landslide kills four people at Paris Beach, north Sumatra.

Four people were killed in a landslide at Paris Beach on the shores of Lake Toba, near Nagori Tiga Ras in north Sumatra, at about 11.00 pm local time (about 4.00 pm...

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Magnitude 2.1 Earthquake near Bromyard in Herefordshire, England.

The British Geological Survey recorded a Magnitude 2.1 Earthquake at a depth of 4 km, about 1 km to the north of Bromyard in Herefordshire, England, at about 1.25 pm GMT on Wednesday 25 February 2015. This quake is not large enough to have caused any damage or injuries, but may have been felt locally.

The approximate location of the 25 February 2015 Bromyard Earthquake. Google Maps.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone to quakes than the rest of Wales or most of England. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic presures tend to build up for longer periods of time between events, so that when they occur more pressure is released.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

See also...

Magnitude 2.0 Earthquake near Blaengarw, South Wales.

The British Geological Survey recorded a Magnitude 2.0 Earthquake at a depth of 4 km, about 1.5 km to the north of Blaengarw in Bridgend, South Wales, slightly...

Magnitude 1.8 Earthquake near Gloucester, southwest England.

The British Geological Survey recorded a Magnitude 1.8 Earthquake at a depth of 15 kn, slightly to the northwest of Gloucester in southwest England, at about 7.20...

Magnitude 1.9 Earthquake in Caerphilly, South Wales.

The British Geological Survey recorded a Magnitude 1.9 Earthquake at a depth of 6 km, about 1 km to the east of...

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Thursday, 26 February 2015

The diet of breeding Grass Owls in Thailand.

Grass Owls are members of the Barn Owl family, Tytonidae, distinguished by their habit of roosting and nesting in tall grasses or other ground-cover plants, rather than trees. Until fairly recently all Grass Owls were thought to belong to a single species, but there are now two species recognised, the African Grass Owl, Tyto capensis, which is found across much of Africa, and the Eastern Grass Owl, Tyto longimembris, which is found in south China, Nepal, India, Myanmar, Southeast Asia, Indonesia, the Philippines, New Guinea, New Caledonia and Australia. The Eastern Grass Owl was first discovered in Thailand as recently as 2006, where a small colony was found nesting in a small area of marsh grassland called Nong Lom in Mae Jan District in Chiang Rai Province in the north of the country.

In a paper published in the Raffles Bulletin of Zoology on 17 February 2015, Akalak Kunsorn of the Department of Biology at Chiang Mai University and the Environmental Ornithology Research Unit at Mahidol University, Siriwadee Chomdej of the Department of Biology and the Materials Science Research Center at Chiang Mai University, Narit Sitasuwan, Prasit Wangpakapattawong and Chatmongkon Suwannapoom, also of the Department of Biology at Chiang Mai University and Brett Sandercock of the Division of Biology at Kansas State University, describe the results of a study of the diet of the Grass Owls of Nom Long carried out by examining Owl pellets from the site during the breeding season.

Eastern Grass Owl, Tyto longimembris, in flight. Rob Hutchinson/The Owl Pages.

Birds lack teeth with which to process food like mammals, instead grinding it up in a muscular gizzard before it is passed to the stomach. As flying animals they are obliged to keep their weight to a minimum, and therefore need to dispose of inedible parts of their prey as quickly as possible, and so both Owls and Raptors regurgitate pellets comprising indigestible items such as fur and bone without passing them through the stomach and gut.

As well as Grass Owls the Nom Long site is also home to four species of Harriers; the Eastern Marsh Harrier, Circus spilonotus, the Pied Harrier, Circus melanoleucos, the Hen Harrier, Circus cyaneus and the Western Marsh Harrier, Circus aeruginosus. Grass Owl pellets tend to be larger and more elongate than Harrier pellets, but to avoid confusion Kunsorn et al. collected pellets only from the nests of Owls.

Kunsorn et al. carried out DNA tests on bones recovered from Owl pellets at Nom Long, in order to determine identify animals being consumed by the Owls. They were able to identify three species of Rodent by this method, the Black Rat, Rattus rattus, the Asian House Mouse, Mus musculus, and the Ricefield Mouse, Mus caroli. In addition wings and tails of Barn Swallows, Hirundo rustica, were also found in the Owl nests, suggesting that these Birds were also being consumed.

Pellets of the Eastern Grass Owl, Tyto longimembris, collected from nests at Nom Long. Kunsorn et al. (2015).

The diet of Eastern Grass Owls has previously been studied in southern Taiwan, where they were found to be consuming Lesser Rice-field Rats, Rattus losea, Ricefield Mice, Mus caroli, Formosan Blind Moles, Mogera insularis, House Shrews, Suncus murimus, Shrews Crocidura spp. and juvenile Formosan Hares, Lepus sinensis, as well as small Birds. This is a far larger range of prey than consumed at the Thai site, which Kunsorn et al. attribute to the more varied hunting grounds available to the Taiwan Owls. Nom Long is largely surrounded by grasslands and wetlands, with some Orange orchard about a kilometre away to the northwest, while the Taiwan site was within easy reach of shrubland, Rice paddies, Bamboo forest, Sugarcane fields, Mango orchards and Human settlements.

Asteroid 2014 EK24 passes the Earth.

Asteroid 2014 EK24 passed by the Earth at a distance of 6 129 000 km (15.94 times the average distance between the Earth and the Moon, or 4.1% of the average distance between the Earth and the Sun), slightly after 5.30 pm GMT on Monday 23 February 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented minor threat. 2014 EK24 has an estimated equivalent diameter of 43-140 m (i.e. it is estimated that a spherical object with the same volume would be 43-140 m in diameter), and an object towards the upper end of this range would pass through the atmosphere and directly impact the ground with a force of about 70 megatons (about 4100 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater over two kilometers across.

The calculated orbit of 2014 EK24. JPL Small Body Database.

2014 EK24 was discovered on 10 March 2014 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2014 EK24 implies that it was the 610th asteroid (asteroid K24) discovered in the first half of March 2014 (period 2014 E).

2014 EK24 has an 368 day orbital period and an eccentric orbit tilted at an angle of 4.7° to the plane of the Solar System, which takes it from 0.93 AU from the Sun (i.e. 93% of the average distance at which the Earth orbits the Sun) to 1.08 AU from the Sun (i.e. 108% of the average distance at which the Earth orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in March 2014 and the next predicted in February 2016.

See also...

Asteroid 2015 DU passes the Earth.

Fireball over Pennsylvania.

A meteor estimated to be 60 cm across and to weigh in excess of 225 kilograms was observed over southwestern Pennsylvania early in the morning of Tuesday 17 February 2015. Scientists at the...

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Flights disrupted following eruption on Mount Popocatépetl.

Flights from Puebla International Airport in Mexico have been cancelled after an eruption from Mount Popocatépetl covered runways in ash on Tuesday 24 February 2015. The eruption also produced an ash column 4 km high, as well as throwing hot rocks and debris up to 700 m from the crater. Ash drifted to the south and east following the eruption, leading to ashfalls in a number of nearby towns. This is the second time flights from Puebla International have been disrupted by Popocatépetl this year, the first having occurred following an eruption on 15 January. Popocatépetl is one of Mexico's most active volcanoes, having been erupting more-or-less continuously since 1994.

Ash column over Mount Popocatépetl at 9.00 am local time on 25 February 2015, as seen from San Nicolas de los Ranchos, Puebla. Webcams de Mexico.

Volcanic ash is extremely hazardous to aircraft in a number of ways. At its most obvious it is opaque, both visually and to radar. Then it is abrasive, ash particles physically scour aircraft, damaging components and frosting windows. However the ash is most dangerous when it is sucked into jet engines, here the high temperatures can melt the tiny silica particles, forming volcanic glass which then clogs engine. When this happens the only hope the aircraft has is to dive sharply, in the hope that cold air passing through the engine during the descent will cause the glass to shatter, allowing the engine to be restarted.

Major eruptions on Popocatépetl are a cause for concern as the volcano is in a densely populated area, with 30 million people living within the potential hazard zone. The last major eruption, a Plinian (or Vesuvian) event in about 800 AD, triggered a series of pyroclastic flows and lahars that scoured the basins around the volcano.

The location of Popocatépetl. Google Maps.

The volcanoes of the Trans-Mexican Volcanic Belt (including Popocatépetl) are fueled by the subduction of the Cocos Plate beneath the North American Plate along the Middle American Trench to the south of Mexico. As the subducting plate sinks into the Earth it is melted by the heat and pressure, and volatile minerals liquify and rise through the overlying North American Plate as magma, fueling Mexico's volcanoes.

See also...

Eruptions on Mount Popocatépetl.

Mount Popocatépetl in southern Mexico has undergone a series of violent eruptions over the past few days, according to the Centro Nacional de Provención de Desastres, the national agency in Mexico responsible for monitoring volcanic activity. The eruptions...

Fresh eruption on Mount Popocatépetl disrupts flights around Mexico City.

Fights in and out of Mexico City were cancelled on Thursday and Friday 5 and 6 July 2013, after Mount Popocatépetl, 65 km to the southeast, began a new round of eruptions with an ash column rising...

Eruption on Mount Popocatépetl.

The central Mexican volcano Popocatépetl began erupting explosively at about 7.30 pm local time on Tuesday 7 May 2013 (12.30 am on Wednesday May GMT), throwing lumps of incandescent rock up to 700 m from the crater and throwing a column of ash 7.6 km...

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Magnitude 2.0 Earthquake near Blaengarw, South Wales.

The British Geological Survey recorded a Magnitude 2.0 Earthquake at a depth of 4 km, about 1.5 km to the north of Blaengarw in Bridgend, South Wales, slightly after 10.40 am GMT on Wednesday 25 February 2015. An Earthquake of this size is not dangerous, and is highly unlikely to have caused any damage or injuries, but people reported feeling this event as far away as Maesteg, about 8 km to the southwest.

The approximate location of the 25 February 2015 Blaengarw Earthquake. Google Maps.

See also...

Magnitude 1.8 Earthquake near Gloucester, southwest England.

The British Geological Survey recorded a Magnitude 1.8 Earthquake at a depth of 15 kn, slightly to the northwest of Gloucester in southwest England, at about 7.20...

Magnitude 1.9 Earthquake in Caerphilly, South Wales.

The British Geological Survey recorded a Magnitude 1.9 Earthquake at a depth of 6 km, about 1 km to the east of...

Magnitude 1.1 Earthquake in southwest Herefordshire, England.

The British Geological Survey recorded a Magnitude 1.1 Earthquake at a depth of 7 km in southwestern Herefordshire, England, slightly before 10.00 pm...

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