Tuesday, 25 July 2017

Magnitude 2.3 Earthquake in the Scottish Highlands.

The British Geological Survey recorded a Magnitude 2.3 Earthquake at a depth of about 7 km about a kilometre to the northwestt of the village of Badrallach on the west coast of the Highland Region of Scotland, slightly before 8.00 am British Summertime (slightly before 7.00 am GMT) on Sunday 23 July 2017. This was not a major event, and presented no threat to human life or property, but was felt in several towns and villages in the area.

The approximate location of the 23 July 2017 Ballrallach 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. 
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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Monday, 24 July 2017

Asteroid 2017 NS5 passes the Earth.

Asteroid 2017 NS5 passed by the Earth at a distance of about 5 136 000 km (13.4 times the average distance between the Earth and the Moon, or 3.43% of the distance between the Earth and the Sun), at about 8.10 am GMT on Monday 17 July 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. 2017 NS5 has an estimated equivalent diameter of 138-410 m (i.e. it is estimated that a spherical object with the same volume would be 138-410 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 3000-165 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 2-7 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

 Image of 2017 NS5 taken with the iTelescope T17 Deep Field Research Telescope at Siding Spring Observatory in New South Wales on 11 July 2017. The image is a composite of six fifty second exposures, the dotted lines being stars which have moved over the course of the exposures and the asteroid the faint object inset indicated by the arrow. Marian Urbanik/iTelescope/Fotografický občasník.

2017 NS5 was discovered on 10 July 2017 (seven days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 NS5 implies that it was the 143rd asteroid (asteroid S5) discovered in the first half of July 2017 (period 2017 N).

The calculated orbit of 2017 NS1. Minor Planet Center.

2017 NS1 has a 353 day orbital period, with an elliptical orbit tilted at an angle of 44.0° to the plain of the Solar System which takes in to 0.72 AU from the Sun (72% of the distance at which the Earth orbits the Sun; slightly inside the orbit of the planet Venus) and out to 1.23 AU (23% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in July 2016 and the next predicted in July 2018. 2017 NS1 also has occasional close encounters with the planet Venus, with the next predicted for February 2148. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2017 NS1 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2017 NS1 is also classified as a Potentially Hazardous Asteroid.

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Caliothrips chiapas: A new species of Thrips from Mexico.

Thrips are tiny (usually less than one millimetre) Insects with greatly reduced wings that resemble feathery stubs. They are plant-parasites, with some species being significant agricultural pests, but due to their small size are often overlooked, and apart from a few species with major economic impact, are not well studied. The genus Caliothrips is apparently one of the best known Thrips groups, with twenty-two described species from across the tropics, however almost nothing is known about most of these species beyond brief descriptions made when they were named.

In a paper published in the journal Zootaxa on 12 July 2017, Laurence Mound of the Australian National Insect Collection, and Francisco Infante of El Colegio de la Frontera Sur describe a new species of Caliothrips from Chiapas State in southern Mexico.

The new species is named Caliothrips chiapas in reference to the state where it was discovered. The species is brown and yellow in colour with females reaching slightly over a millimetre in length, and the males a little smaller. The species was found living on the leaves of the Little Sunflower (Girasolillo), Tithonia tubiformis, but, significantly, not on its flowers, nor on any other species of plant found nearby. Interestingly the flowers were home to a range of other Thrips, none of which were found on the leaves. This suggests that Thrips are particular, not just in what plants they live upon, but in what plant of the plant they inhabit. Such information is recorded for very few species of Thrips, with many species, particularly in the tropics, known only from individuals obtained by beating plants to see what drops out. 

Caliothrips chiapas, host-plant and immatures. (1) Tithonia tubiformis. (2) Caliothrips chiapas larvae on leaf. (3) Caliothrips chiapas slide-mounted second instar larva. Mounde & Infante (2017).
Caliothrips chiapas was found growing on plants around the edge of a Pineapple field in the municipality of Frontera Hidalgo in Chiapas State, close to the border with Guatemala.

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Sunday, 23 July 2017

Three miners confirmed dead and one still missing after Earthquake-induced collapse at South African gold mine.

Three workers have been confirmed dead and one is still missing following an Earthquake-induced collapse at the Tau Lekoa Gold Mine at Orkney in North West Province on Saturday 22 July 2017. The incident was triggered by a Magnitude 0.8 Earthquake, while the men were 1350 m below the ground. Rescue workers are continuing to search for the missing man.

The location of the Tau Lekoa Gold Mine. Google Maps.

Earthquakes are rare in South Africa. Because of this rarity it is hard to make precise judgements about the cause of quakes in South Africa, due to a paucity of data. Northwestern South Africa is close the southern end of the Great Rift Valley exits the continent and passes out under the Indian Ocean. The Great Rift Valley is slowly splitting the African Plate in two allow a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.

Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.

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Sinkhole swallows car in El Paso, Texas.

A female driver had to be rescued after her car was swallowed by a sinkhole in El Paso, Texas, on Saturday 22 July 2017. The woman was manoeuvring in the vehicle when the road began to collapse beneath it. She exited the car and was pulled out of the hole by passers by with only minor injuries, with the subsidence continuing and dragging the vehicle some way further into the ground.

Sinkhole in El Paso, Texas, on 22 July 2017. KFOX 14.

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 22 July 2017 El Paso sinkhole. Google Maps.

On this occasion the sinkhole was caused by the collapse of an overloaded storm drain beneath the road, releasing water that washed away soft sediments under the road. The incident happened amid heavy rains that caused several flash flooding incidents in the area. 

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