Thursday, 16 November 2017

Eruption on Mount Dempo, Sumatra.

The Badan Nasional Penangulanggan Bencana (Indonesia's Disaster Mitigation Agency)has reported an eruption on Mount Dempo, a 3173 m stratovolcano (cone shaped volcano made up of layers of ash and lava) in South Sumatra, on Thursday 9 November 2017. The eruption began slightly after 4.50 pm local time, and produced a dense ash plume that rose about a kilometre above the summit of the volcano and drifted to the south.

Ash column over Mount Dempo, Sumatra, on 9 November 2017. Detik News.

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighbouring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fuelling the volcanoes of Sumatra.

  The Subduction zone beneath Sumatra. NASA/Earth Observatory.

This does not happen at a 90° angle, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

 The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

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Wednesday, 15 November 2017

The Leonid Meteors.

Each year between 15 and 18 November (approximately), typically peaking between midnight and dawn on 17 November, the the Earth encounters the Leonid Meteors, one of the more spectacular of the annual meteor showers, and viewing could be good this year as the shower peaks just before the New Moon on 18 November. Unlike most such showers, which are essentially composed of dust particles, the Leonids comprise particles of up to 8 mm across and up to 85 g in mass, leading to some spectacular fireballs, and each year the shower is thought to deposit 12-13 tonnes of material on the Earth. The Leonid Meteor Shower is so called because the meteors they appear to originate in the constellation of Leo. (Note a meteor is a 'shooting star', a piece of material visibly burning up in the atmosphere and detectable via the light it produces when doing this; a meteorite is a piece of rock that has fallen from the sky and which a geologist can physically hold; and an asteroid is a chunk of rock in orbit about the Sun, to small to be regarded as a planet.

The radiant point (apparent point of origin) of the Leonid Meteors.

The Leonid Meteors are thought to originate from the tail of Comet 55P/Tempel-Tuttle, which orbits the Sun every 33 years, on an orbit that brings it slightly within the orbit of the Earth then out to slightly beyond the orbit of Uranus. Comets are composed largely of ice (mostly water and carbon dioxide), and when they fall into the inner Solar System the outer layers of this boil away, forming a visible tail (which always points away from the Sun, not in the direction the comet is coming from, as our Earth-bound experience would lead us to expect). Particles of rock and dust from within the comet are freed by this melting (strictly sublimation) of the comet into the tail and continue to orbit in the same path as the comet, falling behind over time. 

 Image of Comet 55P/Tempel-Tuttle taken in February 1998 from the National Astronomical Observatory of Japan. Cometography.

The material in the meteor shower is densest close behind the comet, and, since Comet 55P/Tempel-Tuttle has a 33 year orbit, the Leonid Meteor Shower has a 33-year cycle, with a particularly spectacular display every thirty-third year, then a gradual decline in meteor number till the end of the cycle. The last such peak year was in 1998.

Comet 55P/Tempel-Tuttle was discovered in December 1865 by German astronomer Wilhelm Tempel, and independently in January 1866 by the American Horace Parnell Tuttle. The designation 55/P implies that it is a Periodic Comet (comet with an orbital period of less than 200 years), and that it was the 55th such body discovered. As a Comet with a Period of less than 200 years and more than 20 years it is also regarded as a Halley-type Comet.

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Ocyale ghost: A new species of Wolf Spider from Madagascar.

Wolf Spiders, Lycosidae, are large, active Spiders that do not build webs, ambushing animals that passes close to their burrows or actively seeking out and chasing down prey. They have large prominent eyes, and a habit of carrying their eggs in a sack on their abdomens. Members of the genus Ocyale are found in Africa, Asia and the America's though it is thought likely that all American and possibly Asian species may have been placed in this genus erroneously.

In a paper published in the European Journal of Taxonomy on 3 October 2017, Merlijn Jocque of the Biodiversity Inventory for Conservation, Operation Wallacea, and Aquatic and Terrestrial Ecology at the Royal Belgian Institute of Natural Sciences, Siel Wellens, also of Biodiversity Inventory for Conservation and Operation Wallacea, J Andianarivosoa and Felix Rakotondraparany of Mention Zoologie et Biologie Animale at the Université d’Antananarivo, Sam The Seing of Development and Biodiversity Conservation Action for Madagascar, and Rudy Jocqué of the Royal Museum for Central Africa, describe a new species of Ocyale from Mahajanga Province in Madagascar.

The new species is named Ocyale ghost, in reference to its white colour and in addition the white Wolf 'Ghost in the book Game of Thrones by George R.R. Martin. It is a moderately large Spider, with males reaching 16.76–19.45 mm and females 16.47–22.01 mm, creamy white in colour with darker spots and yellow rings around the eyes. The species was found only on the white sandy beaches surrounding Lake Matsedroy.

Ocyale ghost, female photographed at type locality. Jocque et al. (2017).

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Tuesday, 14 November 2017

Fragments of metorite found in British Columbia,.

Researchers from the University of Calgary have found a number of fragments of meteorite believed to have come from an object that entered the atmosphere over British Colombia on 29 September 2017. The object entered the atmosphere roughly above the town of Boswell and exploded 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) close to Meadow Creek., a distance of about 100 km. The meteor is described as initially burning green, then orange, with people close to the termination point reporting a loud explosion. Following a search a number of fragments of rock believed to have come from the object have been found on private land near Crawford Bay, roughly 30 km to the south of Meadow Creek.

Fragment of meteorite found near Crawford Bay, British Columbia, and thought to have come from the 29 September 2017 meteor. Surrey Now-Leader.

A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry.

 Fireball meteor near Nelson in British Colombia on 4 September 2017. Rafael Pern/Twitter.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.

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Monday, 13 November 2017

Woman killed in landslide at illegal quarry in Sylhet Division, Bangladesh.

A woman has died and three other people have been injured in a rockfall at an illegal quarry in the Sylhet District of Sylhet Division in Bangladesh, on Monday 13 November 2017. The incident happened at about 9.30 am local time, as the workers were digging out rocks from a bank of Piyain River. The deceased woman has been identified as Shompa Das, 17, from Netrokona, while the injured persons were Jyoti Bikash, Dipto Sarkar and Ajit Sarkar. This incident brings the number of known deaths in such quarries in Bangladesh to 29 so far this year and eight so far this month.

The approximate location of the 13 November 2017 Sylhet Landslide. Google Maps.

Illegal quarrying for stone used in the building industry is a major problem in Sylhet, with hills and river beds the usual targets. The situation has caused major environmental issues in the region, with a number of hills having disappeared completely. The illegal nature of the quarries adds to the dangerous nature of the work; the quarries not only lack any form of health and safety management, they are often also active in the hours of darkness without lighting in order to avoid detection.

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Magnitude 7.3 Earthquake in Kermanshah Province, Iran.

The United States Geological Survey recorded a Magnitude 7.3 Earthquake at a depth of 23.2 km in about in Kermanshah Province, Iran, close to the border with Iraq, slightly before 9.20 pm local time (slightly before 6.20 pm GMT) on Sunday 12 November 2017. The event is thought to have caused at least 460 deaths and 6700 injured on both sides of the border, with the majority in Kermanshah Province. In addition around 7000 people are believed to have been made homeless. The quake was felt as far away as Ankara, Cairo, Jeddah and Dubai.

Damage to buildings in the city of Sarpol-e-Zahab in Kermansha following the 12 November 2017 Earthquake. Pouria Pakizeh/ISNA/AP.

Iran is situated on the southern margin of the Eurasian Plate. Immediately to the south lies the Arabian Plate, which is being pushed northward by the impact of Africa from the south. This has created a zone of faulting and fold mountains along the southwest coast of the country, known as the Zagros Thrust Belt, while to the northeast of this the geology is dominated by three large tectonic blocks, the Central Iran, Lut and Helmand, which move separately in response to pressure from the south, stretching and compressing the rock layers close to the surface and creating frequent Earthquakes, some of which can be very large.

 The movement of the Arabian Plate and extent of the Zagros Thrust Belt. Rasoul Sorkhabi/Geo ExPro.

To the northeast of this the geology is dominated by three large tectonic blocks, the Central Iran, Lut and Helmand, which move separately in response to pressure from the south, stretching and compressing the rock layers close to the surface and again creating frequent Earthquakes.

The population of Iran is particularly at risk from Earthquakes as, unlike most other Earthquake-prone nations, very few buildings in the country are quake-resistant. The majority of residential buildings in Iran are made of mud-brick, a building material particularly vulnerable to Earthquakes as the bricks often liquefy, trapping people inside and quickly asphyxiating them with dust. This is particularly dangerous at night when the majority of people are inside sleeping.

Section through the Zagros Fold Belt. Sarkarinejad & Azizi (2007).

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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Sunday, 12 November 2017

Eddianna gaspiana: A new species of Rhyniopsid Plant from the Early Devonian Battery Point Formation of Quebec.

The first Vascular Plants appeared some time in the Silurian, but the group did not apparently become a significant part of terrestrial ecosystems until the Early Devonian, when they underwent a major radiation, with a number of new groups appearing. One of these groups was the Rhyniopsids, simple Plants which lacked roots or leaves, but which did have simple stems with some vascular tissue.

In a paper published on the bioRxiv beta database at Cold Spring Harbour Laboratory on 9 October 2017, Kelly Pfeiler and Alexandru Tomescu of the Department of Biological Sciences at Humboldt State University describe a new species of Rhyniopsid Plant from the Early Devonian Battery Point Formation of Quebec.

The new species is named Eddianna gaspiana, where 'Eddianna'  honours Dianne Edwards of Cardiff University, for her work on Silurian and Devonian Plants, and 'gaspiana' refers to the Gaspé Peninsula in Quebec, where the Battery Point Formation outcrops and the specimens from which the new species is named were collected. The species is described from eighteen specimens, all preserved as calcareous cellular permineralizations within four cobbles. The stems of the plant are up to 2 mm in diameter, possibly larger, with a central xylem strand that takes up about 80% of the area, surrounded by layer of phloem 1-3 cells thick, then a ridged cortex.

Eddianna gaspiana gen. (A), (B) Axis cross sections exhibiting large primary xylem with potential centrarch maturation cylinders separated from thin, irregular sclerenchymatous cortex by a thin layer of phloem; note incomplete preservation of xylem at centre in (B). (C), (D) same images as in A and B, respectively, colourised to emphasise concentric zonation of the metaxylem, with larger tracheids in the outer zone (yellow) and narrower tracheids in the inner zone (brown); a thin discontinuous layer of very fine tracheids (more conspicuous in (B) and (D)) marks the border between the two zones; note subtle radial patterning of tracheids, locally, in the outer zone, and pattern of decreasing tracheid diameter toward xylem periphery. Scale bars are 300 μm. Pfieler & Tomescu (2017).

The thick cortex of Eddianna gaspiana suggests that these stems were not able to photosynthesise, while the high proportion of xylem suggests that they had a high capacity for water transport, which in turn suggests that these stems are the lower part of a larger plant that has not been preserved, used to convey water up to the photosynthetic part.

Eddianna gaspiana. (A), (B) Longitudinal sections of axis showing (right to left in (A) and left to right in (B)) metaxylem tracheids (light brown) with conspicuous helical wall thickenings; phloem layer (light brown) with narrow cells and fine, straight vertical cell walls; and incompletely preserved sclerenchymatous cortex (dark brown). Scale bars are 50 μm. (C) Longitudinal radial section of axis with large xylem strand (protoxylem compressed, distorted at centre); sclerenchymatous cortex (dark brown, at left and right); and thin phloem sandwiched between xylem and cortex; note conspicuous helical thickenings of metaxylem tracheids and fine band of much narrower tracheids (between arrowheads) between the two concentric zones of the metaxylem. Scale bar is 150 μm. (D) Scanning electron micrograph of tracheids with helical wall thickenings, note spongy structure of the thickenings, characteristic of Sennicaulis-type tracheids. Scale bar is 10 μm. Pfieler & Tomescu (2017).

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