Tuesday, 19 November 2019

Fifteen killed in explosion at coal mine in Shanxi Province, China.

Fifteen coal miners have died and another nine have been injured in an explosion at an underground mine in Pingyao County in Shanxi Province, China. The incident happened at about 1.50 pm local time on Monday 18 November 2019, at the Feng Yan Group-operated mine. Another eleven miners who were below ground at the time of the incident were unharmed.

Rescue workers entering a mine in Pingyao County, Shanxi, following an explosion on 18 November 2019. Yang Chenguang/Xinhau.

Coal is formed when buried organic material, principally wood, in heated and pressurized, forcing off hydrogen and oxygen (i.e. water) and leaving more-or-less pure carbon. Methane is formed by the decay of organic material within the coal. There is typically little pore-space within coal, but the methane can be trapped in a liquid form under pressure. Some countries have started to extract this gas as a fuel in its own right. When this pressure is released suddenly, as by mining activity, then the methane turns back to a gas, expanding rapidly causing, an explosion. This is a bit like the pressure being released on a carbonated drink; the term 'explosion' does not necessarily imply fire in this context, although as methane is flammable this is quite likely.

 Rescue workers entering a mine in Pingyao County, Shanxi, following an explosion on 18 November 2019. Yang Chenguang/Xinhau.

Coal is also comprised more or less of pure carbon, and therefore reacts freely with oxygen (particularly when in dust form), to create carbon dioxide and (more-deadly) carbon dioxide, while at the same time depleting the supply of oxygen. This means that subterranean coal mines need good ventilation systems, and that fatalities can occur if these break down.

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Monday, 18 November 2019

Avalanche kills six on the Siachen Glacier in Jammu and Kashmir.

Four Indian soldiers and two civilian porters have been killed in an avalanche on the northern part of the Siachen Glacier in Jammu and Kashmir, India, on Monday 18 November 2019. The casualties were part of a patrol that was hit by the avalanche at about 3.00 pm, local time, in an area at an altitude of 5800 m above sealevel. All of those caught in the avalanche were evacuated by helecopter, but only after several hours, which is likely to have been a contributing factor in the loss of life in an area where temperatures can drop to -60°C at night. Seven other soldiers are described as being in a critical condition.

The approximate location of the 18 November 2019 Siachen Glacier avalanche. Google Maps.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

  Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

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Magnitude 5.6 Earthquake off the east coast of Guam.

The United States Geological Survey recorded a Magnitude 5.6 Earthquake at a depth of 66.8 km about 40 km off the east coast of the island of Guam, a US possession in the Mariana Islands, at about 9.55 am local time on Monday 18 November 2019 (about 11.55 pm on Sunday 17 November GMT). There are no reports of any casualties this event, though people have reported feeling the event across much of the island.

The approximate location of the 18 November 2019 Guam Earthquake. USGS.

The volcanic Mariana Islands are located on the eastern margin of the Philippine Plate, close to its margin with the Pacific Plate. The Pacific Plate is being subducted beneath the Philippine Plate along the Mariana Trench. This is not a smooth process, an the plates constantly stick together then break apart again as the pressure builds up, resulting in Earthquakes.

 Simplified diagram of the subduction of the Pacific Plate beneath the Philippine plate, and how this fuels the volcanoes of the Mariana Islands. NOAA Ocean Explorer.

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

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Sunday, 17 November 2019

The Leonid Meteors.

Each year between 6 and 30 November (approximately) the the Earth encounters the Leonid Meteors, one of the more spectacular of the annual meteor showers, with peak activity this year expected before dawn on Monday 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. Greg Smye-Rumsby/Astronomy Now.

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. 

 The orbit and current position of Comet 55P/Tempel-Tuttle. The Sky Live 3D Solar System Simulator.

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.

Image of Comet 55P/Tempel-Tuttle taken on 31 January 1998, 60 second exposure. Martin Mobberley.

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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Third case of Plague reported in China.

A third case of plague has been reported in China, with a 55-year-old man in Inner Mongolia reportedly being treated for the Bubonic form of the disease, which he is believed to have contracted after eating a wild-caught Rabbit earlier this month. This follows the two cases of the disease that were reported in Beijing earlier this week, with both patients also from Inner Mongolia and suffering from the Pneumonic form of Plague having been brought to a hospital in the city for specialist treatment. All three patients are being treated in isolation, with a number of people who have come into contact with them being monitored for symptoms. Pneumonic Plague is a variety of the disease, which infects the lungs and is spread through coughing, rather than the more usual Bubonic variety, which infects the lymph-nodes and is typically spread via the exchange of bodily fluids via a parasite vector such as a Flea.

Plague is caused by Yersinia pestis, the same Bacterium that causes Bubonic Plague. The Bacterium is indigenous to northern China, Mongolia, and the Russian Far East, with outbreaks of Plague being a regular occurrence. Yersinia pestis generally responds well to antibiotics, but the alarm caused by the diseases it causes can provoke excessive use, leading to shortages when they are most needed. The most recent fatalities due to the disease in the region having happened in April this year, when two Russian citizens died of the disease in Mongolia, and the most recent fatality in China having happened in Gansu Province in 2014. Due to its high mortality and transmission rates outbreaks of Plague are always concerning, though the apparent ability of the Chinese healthcare system to contain an outbreak without fatalities is encouraging.

 Mass of Yersinia pestis Bacteria. Wikipedia.

Yersinia pestis is a Gram-negative, facultatively anaerobic (i.e. capable of using oxygen, but not needing it), rod-shaped Gammaproteobacteria, related to other pathogenic Bacteria such as Vibrio cholerae (Cholera), and Esherchia coli (food poisoning).It is a zoonotic disease, naturally occurring in a variety of Rodents, but capable of infecting Humans, typically via Fleas, which spread the disease by biting both their regular Rodent hosts and Humans. Zoonotic diseases can be particularly dangerous, as Humans are not part of their natural life-cycle, with the effect that they are not under evolutionary pressure to keep Human hosts alive in order to perpetuate themselves. Such diseases typically have short duration and a high fatality rate, though epidemics usually burn out quickly.

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Saturday, 16 November 2019

Asteroid 2019 VB5 passes the Earth.

Asteroid 2019 VB5 passed by the Earth at a distance of about 145 800 km (0.38 times the average  distance between the Earth and the Moon, or 0.10% of the distance between the Earth and the Sun), slightly before 5.30 pm GMT on Saturday 9 November 2019. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2019 VB5 has an estimated equivalent diameter of 1-3 m (i.e. it is estimated that a spherical object with the same volume would be 1-3 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 more than 45 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2019 VB5. JPL Small Body Database.

2019 VB5 was discovered on 8 November 2019 (the day after its closest encounter with the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2019 VB5 implies that the asteroid was the 122nd object (asteroid Y7 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that B5 = (24 x 5) + 2 = 122) discovered in the first half of November 2019 (period 2010 V).

2019 VB5 has a 402 day orbital period and an eccentric orbit tilted at an angle of 0.88° to the plane of the Solar System, which takes it from 0.84 AU from the Sun (i.e. 84% of he average distance at which the Earth orbits the Sun) to 1.28 AU from the Sun (i.e. 128% 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 2019 UY7 occasionally comes close to the Earth, with the last such encounter having happened in April 2010, and the next predicted for October 2020.

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Sixty people forced to evacuate their homes following mudslide in Nottinghamshire, England.

Sixty people from nineteen homes have been forced to evacuate their homes following a mudslide at a housing development in a former quarry in the town of Mansfield in Nottinghamshire, England. The landslip happened on Thursday 7 November 2019 in the Berry Hill Quarry in the south of the town following several days of heavy rainfall 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. 

Mudslide at a former quarry in Mansfield, England, that led to nineteen homes in the area being evacuated. .

The evacuated residents have been advised that they can claim one-off payments of up to £120 from a Flood Hardship Fund operated by Nottinghamshire County Council, but many are unhappy with this, claiming that Mansfield District Council had failed to respond to concerns raised about the stability of the cliff face from 2017 onwards. Photographs of the area do appear to show a cliff-face comprised largely of unconsolidated sediments close to the rear of the houses, something which was apparently not picked up by a planning process that began with an application for planning permission in 1999 and ended with houses being built in 2011.

Part of the collapsed cliff face visible between two houses at the Berry Hill Quarry in Mansfield, England. BBC.

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