Sunday, 24 September 2017

Magnitude 1.9 Earthquake off the southwest coast of Jersey.

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 Islands slightly before 0.20 am British Summertime (slightly before 1.20 am GMT) on Friday 22 September 2017. 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.
The approximate location of the 22 September 2017 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.
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Saturday, 23 September 2017

Blindness in wild Kiwi.

Birds are considered to have the best vision in any living Vertebrate group, with almost all Birds having large eyes relative to their size and densely packed retinal neurons, along with other specialisations found in different species and groups. This is closely tied to the ecology of Birds, which typically fly, are visual foragers and rely on markings and display to find mates. However, one group of Birds, the flightless Kiwi, Apteryx spp., of New Zealand, appear to break with this pattern, having small eyes relative to their size, under-developed visual regions of the brain and the smallest visual field of any Birds. Kiwi also have a very different feeding ecology to other Birds, being nocturnal foragers on the floor of canopy forests, with highly developed senses of smell hearing and touch, particularly at the tip of the long bill, which has a unique set of mechanoreceptors (touch neurons), raising questions as to how much value vision is to a Kiwi at all.

In a paper published in the journal BMC Biology on 12 September 2017, Bret Moore of the William R. Pritchard Veterinary Medical Teaching Hospital at the University of California-Davis, Joanne Paul-Murphy of the Department of Medicine and Epidemiology, also at the University of California-Davis, Alan Tennyson of the Museum of New Zealand Te Papa Tongarewa, Christopher Murphy of the Department of Surgical and Radiological Sciences at the University of California-Davis, and the Department of Ophthalmology & Vision Science at the University of California-Davis, describe the incidence of widespread visual impairment, including blindness, in a population of wild Okarito Brown Kiwi, Apteryx rowi.

An Okarito Brown Kiwi, Apteryx rowi, on Mana Island, New Zealand, in June 2017. Leon Berard/New Zealand Birds Online.

Out of a population of 160 Kiwi examined, 53 were found to have some form of visual impairment, and four were completely blind. The Birds were found to suffer from a variety of conditions, including corneal opacification and shrunken fibrotic globes. Many of these infections appeared chronic in nature, suggesting that they were long-term conditions that had not had any undue impact on the Bird’s overall health. This included three of the completely blind specimens, which appeared healthy at the time of inspection, and which were shown by radio-tagging to survive for at least four years after the initial inspection, with one of these Kiwi going on to form a pair-bond with a visually healthy individual. 

Normal and pathologic findings for the anterior segment of the Okarito Brown Kiwi. Complete ophthalmic examinations consisted of slit lamp biomicroscopy, direct ophthalmoscopy, and streak retinoscopy. Lack of vision was interpreted by no response to light or motion, combined with the severity of ocular lesions (e.g. inability to visualize intraocular structures beyond the abnormal ocular tissue, such as marked corneal or lens opacification). (a) Normal anterior segment. Note the small palpebral aperture (mean diameter 8.53 ± 0.50 mm SD, n = 9 birds). (b) Nuclear sclerosis: a normal aging change in the lens associated with changes in lens protein composition. Nuclear sclerosis generally has minimal visual consequences in animals. (c) Buphthalmia with marked corneal edema. This animal was blind bilaterally but was in good physical condition. (d) Phthisis bulbi (a globe shrunken with fibrosis). Potential causes include any chronic inflammatory or glaucomatous process or severe trauma. (e), (f) Resorbing, end-stage cataracts. (g) Anteriorly luxated cataract. h Inferiorly luxated cataract. Moore et al. (2017).

From this Moore et al. conclude that the loss of vision has no real impact on Kiwi. They suggest that while the Birds may use vision to determine the difference between night and day, useful for determining when to forage, but do not appear to need working vision to obtain food (indeed they cannot see the tips of their beaks, their principle foraging tool), nor to obtain a mate. They suggest that Kiwi may be in the process of losing their vision by regressive evolution, i.e. vision is no longer being selected for, so the visual abilities of the Birds are slowly degenerating as deleterious mutations build up in the DNA regions which govern vision.

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Landslide kills two in Cebu City. The Philippines.

Two people have been killed and several more have been evacuated after a landslide hit the community of Sitio Lower Ponce in the Capitol Site area of Cebu City, on the Philippine island of the same name. The dead have been named as Elpedio Geraga, 64, and Juvelyn Sanipa, 31. The incident happened at about 8.15 pm on Thursday 21 September 2017, after about five hours of continuous heavy rain. 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. Cebu has a wet and dry tropical climate, with a long rainy season that lasts from May to January. 

 Rescue workers at the site of the 21 September 2017 Cebu landslide. Junjie Mendoza/Cebu Daily News.

Cebu has a tropical climate with distinct wet and dry seasons. The wet season lasts from June to October and brings with it frequent heavy rains and associated problems. The community of Sitio Lower Ponce is an informal settlement (i.e. built without formal permission or adherence to planning rules by members of a poor community) on a 45 degree slope above a road. This site is home to several hundred people, and is prone not just to landslides, but also to floods and fires.

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Friday, 22 September 2017

Asteroid 2017 RJ2 passes the Earth.

Asteroid 2017 RJ2 passed by the Earth at a distance of about 550 500 km (1.45 times the average distance between the Earth and the Moon, or 0.37% of the distance between the Earth and the Sun), slightly before 10.30 pm GMT on Friday 15 September 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 RJ2 has an estimated equivalent diameter of 5-18 m (i.e. it is estimated that a spherical object with the same volume would be 5-18 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 40 and 26 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 RJ2  Minor Planet Center.

2017 RJ2 was discovered on 12 September 2017 (three days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 RJ2 implies that it was the 59th asteroid (asteroid J2) discovered in the first half of September 2017 (period 2017 R).

2017 RJ2 has a 993 day orbital period and an eccentric orbit tilted at an angle of 1.49° to the plane of the Solar System, which takes it from 0.74 AU from the Sun (i.e. 74% of he average distance at which the Earth orbits the Sun, slightly outside the distance at which the planet Venus orbits the Sun) to 3.16 AU from the Sun (i.e. 316% of the average distance at which the Earth orbits the Sun, and more than two times as distant from the Sun than the planet Mars). 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). 

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Thursday, 21 September 2017

Cypria lacrima: A new species of Candonid Ostracod from Hays County, Texas.

Ostracods are small Crustaceans with a bivalved body plan; their body is sandwiched laterally between two large valves, with the animal using its legs to generate a current through the shell, enabling it to feed, and in many cases swim (check). Ostracods are small (seldom much over a millimetre) and can be very abundant, making them common fossils in many deposits. They also often have distinctive shell ornamentation, enabling the identification of species from valves alone, and are both fast-evolving and sensitive to a range of environmental conditions, making them useful in both biostratigraphy (dating rocks using fossils) and palaeoenvironmental reconstruction. The Candonidae are a widespread family of predominantly freshwater Ostracods, being particularly numerous in Eurasia. This group is split into three subfamilies, the marine Paracypridinae and the freshwater Candoninae and Cyclocypridinae, with the Cyclocypridinae being distinguished by swimming setae on second antenna and segmented clasping organs, which the Candoninae lack.

In a paper published in the journal Zoological Studies on  Okan Külköylüoğlu of the Department of Biology at Abant İzzet Baysal University, Derya Akdemir of İstanbul, Mehmet Yavuzatmaca, also of the Department of Biology at Abant İzzet Baysal University, Benjamin Schwartz of the Edwards Aquifer Research and Data Center and Department of Biology at Texas State University, and Benjamin Hutchins of Texas Parks and Wildlife, describe a new species of Ostracod from Hays County in Texas.

The new species is placed in the Candonin genus Cypria and given the name lacrima, meaning 'tear', in reference to the teardrop shape of the shells of the animals. The species was found in artesain wells accessing the Edwards Aquifer near San Marcos in Hays County. These Ostracods reach slightly over half a millimetre in length, and can be distinguished by the shape and unique ornamentation of the carapace.

Cypria lacrima. (A) Dorsal view, (B) external and (C) internal view of left valve, (D) posterior end of right valve, (E) right valve internal view, (F) internal views of anterior, and (G) posterior ends of left valve. Male (A)-(C), (F), (G); female (E), (D). Scale bars: 100 μm for (A)-(C), (E); 50 μm for (F) 20 μm for (D) 10 μm for (G). Arrows show anterior end. Külköylüoğlu et al. (2017).

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Wednesday, 20 September 2017

Magnitude 7.1 Earthquake in Puebla State, Mexico, kills at least 225 people.

The United States Geological Survey recorded a Magnitude 7.1 Earthquake at a depth of 51 km, approximately 55 km to the south of the city of Peubla in the Mexican State of the same name, slightly before 1.15 pm local time (slightly before 6.15 pm GMT) on Tuesday 19 September 2017. The event has caused extensive destruction in the states of Puebla and Morales as well as the Mexico City Federal District, with extensive building collapses in urban areas and 226 confirmed deaths at the time of writing. The event was felt as far away as Austin in Texas and San Salvador in El Salvador.

Collapsed building in Mexico City following the 19 September 2017 Earthquake. Daniel Cardenas/Anadulu/Getty Images.

Mexico is located on the southernmost part of the North American Plate. To the south, along the Middle American Trench, which lies off the southern coast off Mexico, the Cocos Plate is being subducted under the North American Plate, passing under southern Mexico as it sinks into the Earth. This is not a smooth process, and the plates frequently stick together then break apart as the pressure builds up, causing Earthquakes on the process.

The approximate location of the 19 September 2017 Mexico Earthquake. USGS.

The Cocos Plate is thought to have formed about 23 million years ago, when the Farallon Plate, an ancient tectonic plate underlying the East Pacific, split in two, forming the Cocos Plate to the north and the Nazca Plate to the south. Then, roughly 10 million years ago, the northwesternmost part of the Cocos Plate split of to form the Rivera Plate, south of Beja California.

 The position of the Cocos, Nazca and Rivera Plates. MCEER/University at Buffalo.

In a paper published in the Journal of Geophysical Research, in 2012, a team led by Igor Stubailo of the Department of Earth and Space Sciences at the University of California Los Angeles, published a model of the subduction zone beneath Mexico using data from seismic monitoring stations belonging to the Mesoamerican Seismic Experiment, the Network of Autonomously Recording Seismographs, the USArray, Mapping the Rivera Subduction Zone and the Mexican Servicio Sismologico Nacional.

Partially collapsed school in Mexico City following the 19 September 2017 Earthquake. EPA/Shutterstock.

The seismic monitoring stations were able to monitor not just Earthquakes in Mexico, but also Earthquakes in other parts of the world, monitoring the rate at which compression waves from these quakes moved through the rocks beneath Mexico, and how the structure of the rocks altered the movement of these waves.

Collapsed building in the city of Jojutla in Morales State, Mexico, following the 19 September 2017 Earthquake. Carlos Rodriguez/AP.

Based upon the results from these monitoring stations, Stubailo et al. came to the conclusion that the Cocos Plate was split into two beneath Mexico, and that the two plates are subducting at different angles, one steep and one shallow. Since the rate at which a plate melts reflects its depth within the Earth, the steeper angled plate melts much closer to the subduction zone than the shallower angled plate, splitting the Trans-Mexican Volcanic Belt into sections above the different segments of the Cocos Plate, and causing it to apparently curve away from the subduction zone.

  Top the new model of the Cocos Plate beneath Mexico, split into two sections (A & B) subducting at differing angles. (C) Represents the Rivera Plate, subducting at a steeper angle than either section of the Cocos Plate. The Split between the two has been named the Orozco Fracture Zone (OFZ) which is shown extended across the Cocos Plate; in theory this might in future split the Cocos Plate into two segments (though not on any human timescale). Bottom Left, the position of the segments on a map of Mexico. Darker area is the Trans-Mexican Volcanic Belt, orange circles are volcanoes, brown triangles are seismic monitoring stations, yellow stars are major cities. Bottom Right, an alternative model showing the subducting plate twisted but not split. This did not fit the data. Stubailo et al. (2012).

The two major Earthquakes that have happened in Mexico this September, on the seventh and nineteenth of the month, are thought to relate to this fragmenting of the Cocos Plate, with the events thought likely to have been caused by tearing along one of these splits.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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Tuesday, 19 September 2017

Family evacuated after Florida home swallowed by sinkhole

A family have been forced to evacuate their home after is was swallowed by a sinkhole in the city of Apopka in Orange County, Florida, on Tuesday 19 September 2017.  The hole was first noticed slightly after 8.00 am local time, and rapidly expanded to around 7.5 by 3 meters, causing the house to partially collapse into it. It is not clear if the hole has reached its maximum size.

Home in Apopko, Florida, partially engulfed by sinkhole on 19 September 2017. WESH.

Sinkholes are generally caused by water eroding soft limestone or unconsolidated deposits from beneath, causing a hole that works its way upwards and eventually opening spectacularly at the surface. Where there are unconsolidated deposits at the surface they can infill from the sides, apparently swallowing objects at the surface, including people, without trace.

 The approximate location of the 19 September 2017 Apopka sinkhole. Google Maps.

The precise cause of this sinkhole is unclear, but is thought likely to have been caused by high rainfall associated with Hurricane Irma acting on soft limestone deposits in the area. Many parts of Florida are particularly prone to sinkholes, due to the porous limestone that underlies much of the state. This is eroded over time by acid in rainwater (most rainwater is slightly acidic, though pollution can make this worse), and can collapse suddenly, causing overlying sediments to collapse into the hole and a sinkhole to open up. This can be triggered by human activity, such as pumping water out (which causes the water to flow, facilitating acid dissolution of the limestone), but is essentially a natural process. 

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