Sunday, 18 March 2018

Avalanche feared to have killed four skiers in Swiss Alps.

The bodies of two skiers have been recovered from under about six meters of snow, and a further two are missing, following an avalanche in the Vallon d'Arbi area near Riddes in the District of Martigny of Canton Valais in Switzerland on Friday 16 March 2018. All four skiers are said to be aged between 20 and 25 and from the Alsace Region of France.

The scene of an avalanche in Vallon d'Arbi on 16 March 2018. Valais Canton Police.

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.

The Alps have seen a number of avalanche related incidents this winter, largely due to high levels of snowfall. This is, in turn caused by warmer conditions over the Atlantic, which leads to higher rates of evaporation over the ocean, and therefore higher rates of precipitation over Europe, which falls as snow in cooler regions such as the Alps, where the moist air meets cold air fromt the east. This situation is likely to get worst this week after a significant cold front from the east brought plunging temperatures across Europe this week, which is expected to be replaced by a new wet front from the west over the weekend, depositing precipitation as more snow across the now cooler continent. 

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The March Equinox.

The March Equinox falls at 4.15 pm on Tuesday 20 March this year. The Earth spins on its axis at an angle to the plain of the Solar System. This means that the poles of the Earth do not remain at 90° to the Sun, but rather the northern pole is tilted towards the Sun for six months of the year (the northern summer), and the southern pole for the other six months (the southern summer). This means that twice a year neither pole is inclined towards the Sun, on days known as the equinoxes.

The tilt of the Earth relative to the incoming light of the Sun at the March Equinox. Przemyslaw Idzkiewicz/Wikimedia Commons.

The equinoxes fall each year in March and September, with the March Equinox being the Spring (or Vernal) Equinox in the Northern Hemisphere and the Autumn Equinox in the Southern Hemisphere, while the September Equinox is the Autumn Equinox in the Northern Hemisphere and the Spring Equinox in the Southern Hemisphere. On these two days the day and night are both exactly twelve hours long at every point on the planet, the only days on which this happens.

 The tilt of the Earth relative to the Sun at the planet's equinoxes and solstices. Astronomy Group/University of St Andrews.

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Saturday, 17 March 2018

Asteroid 2007 LU19 passes the Earth.

Asteroid 2007 LU19 passed by the Earth at a distance of about 7 851 000 km (20.4 times the average distance between the Earth and the Moon, or 5.25% of the distance between the Earth and the Sun), slightly after 9.20 pm GMT on Saturday 10 March 2018. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. 2007 LU19 has an estimated equivalent diameter of 100-330 m (i.e. it is estimated that a spherical object with the same volume would be 100-330 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 225 to 120 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 1-5 km in diameter and devastation on a global scale, as well as climatic effects that would last years or even decades.

The calculated orbit of 2007 LU19. Minor Planet Center.

2007 LU19 was discovered on 15 June 2007 by the Siding Spring Observatory near Coonabarabran in New South Wales. The designation 2007 LU19 implies that it was the 495th asteroid (asteroid U19) discovered in the first half of June 2007 (period 2007 L). 

2007 LU19 has a 1332 day orbital period and an eccentric orbit tilted at an angle of 2.60° to the plane of the Solar System, which takes it from 0.89 AU from the Sun (i.e. 89% of he average distance at which the Earth orbits the Sun) to 3.84 AU from the Sun (i.e. 384% of the average distance at which the Earth orbits the Sun, and more than twice 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). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in June 2007 and the next predicted in March 2029. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2007 LU19 is also classified as a Potentially Hazardous Asteroid.

2007 LU19 also has frequent close encounters with the planets Mars, which it last came close to in March 1960 and is next predicted to pass in May 2098, and Jupiter which it last came close to in July 1987 and is next predicted to pass in August 2022. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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Hundreds of artefacts stolen from Canterbury Archaeological Trust recovered.

Hundreds of artefact's stolen from the Canterbury Archaeological Trust in Kent, England, in January this year have been recovered by Kent Police. The artefact's were found in an abandoned building a few streets from where they were originally stolen. The recovered items include hundreds of beads and other Anglo-Saxon items from excavations in Canterbury and St Albans (Hertfordshire). Many items are still missing after the break-in, though it is thought that most of these are replica items, such as weapons and coins, from the Trust's educational loans collection, plus modern tools used during archaeological excavations, which may have proved easier for the thieves to sell.

 Members of the Canterbury Archaeological Trust with stolen artifacts recovered by the police this week. Kent Messenger.

The thieves broke into the charity's premises in Canterbury on the night of Thursday 22-Friday 23 January 2018, then again on the night of Friday 23-Saturday 24, causing extensive damage to the charity's building and collection, breaking power and water lines and exposing asbestos, which had to be dealt with by a specialist contractor before other work could proceed. As well as the stolen items, many other artifacts were scattered and mixed, and will take hundreds of hours work by specialist workers to re-identify and properly curate; archaeological artifacts without proper records of their origin are of little value. The recovered items will now have to be treated in the same way, requiring many hours of work by the Trust's employees and volunteers.

Kent Police are still hoping to apprehend the thieves and recover those items that are still missing. Anyone with any information can contact Kent Police on 01843 222289 (+44 1843 222289 from outside the UK) and quote incident number ZY/4200/18. Alternatively Kent Crimestoppers can be called anonymously on 0800 555111 from within the UK only, or online here from anywhere in the world.

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Woman killed by Crocodile in Zambezi District, Zambia.

A woman has died and a second has been badly injured in separate Crocodile attacks in the Zembezi District, of Northwestern Province, Zambia this week. Mijet Mapeni, 20, of Chakujimbula village, was attacked while fishing in the Makondo River, her body being found recovered later. Marjory Njapau, also 20, of Kadiombo village, was attacked while bathing in the Lunuyi stream, and suffered multiple injuries. She is currently being held in Zebezi District Hospital, where her condition is described as stable.

A Nile Crocodile, Crocodylus niloticus, by the Kafue Riverin Zambia. Hans Hillewaert/Wikimedia Commons.

Zambia is home to two Crocodile species, the Nile Crocodile, Crocodylus niloticus, and the Slender Snouted Crocodile, Crocodilus cataphractus, though the later is found only around Lake Bangweulu and the Luapula River in Northern and Luapula Provinces, so the Zambezi District attacks were almost certainly carried out by Nile Crocodiles. Nile Crocodiles are large animals, reaching about five meters in length, and are ambush predators capable of taking large prey, including, on occasion, Humans. The animals are thought to be at their most dangerous around September on the Zambezi, when the water is lowest, and females are guarding eggs buried in nests by the river.
 The location of Zambezi District, where two woman were attacked by Crocodiles this week. Google Maps.
Nile Crocodiles are considered to be of Least Concern under the terms of the  International Union for the Conservation of Nature’s Red List of  Threatened Species, but are still protected in many countries, including Zambia, due to historic hunting which decimated populations in many areas. However, the rising number of attacks on Humans by the animals has led to calls for regulated hunting to be introduced to control the population.
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Meteorite stolen from Virginia museum.

A meteorite has been stolen from the Science Museum of Virginia in Richmond. The rock, which was contained in a metal stand in an exhibit on the museum's first floor was removed some time between 9.30 am and 2.30 pm on Thursday 15 March 2018, by a thief who apparently used some sort of tool to partially dismantle the stand. Virginia Capitol Police are seeking the perpetrator of the crime, however the item, a nickel-iron meteorite about the size of a tennis ball, may be hard to dispose of, as it is not particularly uncommon, giving it a low value (about US$1500) and a limited number of potential buyers. The museum expects to be able to replace the meteorite cheaply and within a few days.

A meteorite that was stolen from the Science Museum of Virginia on 15 March 2018. Virginia Capitol Police.

Nickel-iron meteorites, or octahedrites, are the most common class of meteorite, being comprised largely of iron with a substantial amount of nickel, leading to the formation of the mineral kamacite, which has an octahedral form, giving these meteorites their name. Strictly speaking iron meteorites are less common than stony meteorites, but they are much more commonly found as they are resilient both to atmospheric entry and terrestrial weathering, and relatively easy to recognise. Only about 5.7% of objects entering the atmosphere are thought to be iron meteorites, but they comprise about 90% of objects in collections. Nickel-iron meteorites are the most common form of iron meteorite, though low-nickel meteorites hexahedrites, are also found. Both are thought to have formed within the interior of large planetesimals in the early Solar System. These bodies were large enough to develop differentiated iron cores (as is seen in the Earth today), but which were subsequently torn apart by tidal forces generated by the larger planets.

Anyone with information on the crime can contact the Virginia Capitol Police on (804) 786-2120. 

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Magnitude 1.1 Earthquake in Cheshire, England.

The British Geological Survey recorded a Magnitude 1.1 Earthquake at a depth of about  km, roughly 4 km to the south of the town of Crewe in Cheshire, England, slightly before 10.10 pm GMT on Tuesday 28 February 2018. There are no reports of any damage or injuries associated with this event, and nor would they be expected from such a small event, though may have been felt in the area.
The approximate location of the 15 March 2018 Crewe 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 pressures 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.
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. 

(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.    
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