Thursday, 17 August 2017

Flooding in Bihar State, India, kills at least 98.

At least 98 people have died and over seven million have been forced to flee their homes in flooding across the state of Bihar in India this week. Twenty people are known to have died in Araria District, fourteen in East Champaran, thirteen in West Champaran, twelve in Madhepura, eleven in Sitamarhi, eight in Kisanganj, five each in Purnea and Madhubani, four in Darbhanga, three in Saharsa, two in Sheohar and one in Supual. The flooding has left many more without access to food and clean water, and washed away many roads and railways, leading the Indian National Disaster Response Force to drop supplies by air in areas where local populations cannot be reached in any other way.

People affected by flooding in Bihar State, India, this week. Times Now.

The flooding has been triggered by heavy rainfall in Nepal, associated with the Asian Summer Monsoon, which has caused the Koshi, Mahananda, Gandak, Bagmati and Ganga rivers to swell and breach their banks in many places, and made worse by high rainfall across Bihar itself.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea. 

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

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Wednesday, 16 August 2017

Homes evacuated after sinkhole opens up in Wednesbury, England.

Several homes have been evacuated after a sinkhole opened up in the drive of a house in the Black Country town of Wednesbury, on Saturday13 August 2017.  The hole is about 3 m wide and 3.65 m deep, and has caused a wall to collapse and partially trapped a car that was parked on a neighbouring drive.

Parked car partially trapped by a sinkhole outside a house in Wednesbury, England. ITV News Central.

Sinkholes are typically caused by the erosion of soft sediments or limestone beneath the surface, creating voids that can open up unexpectedly. On this occasion the hole appears to have been triggered by the collapse of a sewer main, which lead to the washing away sediments beneath the road, and triggering the collapse of a water main, leading to further water loss and further erosion, eventually causing the overlying road to collapse.

The approximate location of the August 2017 Wednesbury sinkhole. Google Maps. 

The origin of this particular sinkhole is yet to be determined. It is likely to be related to old coal mineworkings in the area, which was the site of extensive coal mining from the mode nineteenth century onwards, with not all former mines properly recorded, and such mines are prone to collapses, particularly after periods of wet weather. However Wednesbury is also situated on soft limestone, which 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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Magnitude 4.7 Earthquake in Batna Province, Algeria.

The United States Geological Survey recorded a Magnitude 4.7 Earthquake at a depth of 10 km, about 11 km to the northwest of the city of Merouana in Batna Province, Algeria, at about 3.50 pm local time (about 2.50 pm GMT) on Tuesday 15 August 2017. There are no reports of any damage or injuries associated with this event, though people have reported feeling it in Merouana and N'gaous.

The approximate location of the 15 August 2017 Merouana Earthquake. USGS.

Algeria lies on the northernmost part of the African Plate, while southern Europe to the north is part of Eurasia. Africa is pushing into Europe from the south, which causes Earthquakes around the Mediterranean Basin. These are most common in southeast Europe, but those in northwest Africa, while less frequent, are often larger and more deadly.

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Total Solar Eclipse to be visible from United States, 21 August 2017.

A total eclipse of the Sun will be visible from parts of the United States on Monday 21 August 2017, with a partial eclipse visible from the rest of North and Central America, as well as the Islands of the Caribbean, Colombia, Ecuador, Venezuela, Guyana, Suriname, French Guiana, Iceland, Ireland, Scotland, southern Scandinavia and parts of Brazil, Peru and Bolivia and (briefly) England, western Iberia, parts of West Africa and northwest Brazil. 

The path of the 21 August 2017 Solar Eclipse. The total eclipse will be visible along the central dark grey path. A partial eclipse will be visible from the shaded areas; in the lighters area the full eclipse will not be visible as it will have started before dawn (west) or will continue after sunset (east). The red lines are the Equator and the Greenwich Meridian. HM Nautical Almanac Office.

Eclipses are a product of the way the Earth, Moon and Sun move about one-another. The Moon orbits the Earth every 28 days, while the Earth orbits the Sun every 365 days, and because the two Sun and Moon appear roughly the same size when seen from Earth, it is quite possible for the Moon to block out the light of the Sun. At first sight this would seem likely to happen every month at the New Moon, when the Moon is on the same side of the Earth as the Sun, and therefore invisible (the Moon produced no light of its own, when we see the Moon we are seeing reflected sunlight, but this can only happen when we can see parts of the Moon illuminated by the Sun). 

The relative positions of the Sun, Moon and Earth during a Solar eclipse. Starry Night.

However the Moon does not orbit in quite the same plane as the Earth orbits the Sun, so the Eclipses only occur when the two orbital planes cross one-another; this typically happens two or three times a year, and always at the New Moon. During Total Eclipses the Moon entirely blocks the light of the Sun, however most Eclipses are Partial, the Moon only partially blocks the light of the Sun.

How the differing inclinations of the Earth and Moon's orbits prevent us having an eclipse every 28 days. Starry Skies.

Although the light of the Sun is reduced during an Eclipse, it is still extremely dangerous to look directly at the Sun, and viewing eclipses should not be undertaken without appropriate equipment.

 Animation showing the shadow of the Moon at five minute intervals on Friday 20 March 2015. Andrew Sinclair/HM Nautical Almanac.

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Monday, 14 August 2017

Asteroid 2017 PK25 passes the Earth.

Asteroid 2017 PK25 passed by the Earth at a distance of  853 900 km (2.22 times the average distance between the Earth and the Moon, or 0.57% of the average distance between the Earth and the Sun), slightly before 2.10 am GMT on Monday 14 August 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 PK25 has an estimated equivalent diameter of 16-52 m (i.e. it is estimated that a spherical object with the same volume would be 16-52 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 26 and 9 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 PK25 Minor Planet Center.

2017 PK25 was discovered on 12 August 2017 (two days before its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2017 PK25 implies that the asteroid was the 635th object (object K25) discovered in the first half of August 2017 (period 2017 P). 

2017 PK25 has a 268 day orbital period, with an elliptical orbit tilted at an angle of 25.9° to the plain of the Solar System which takes in to 0.46 AU from the Sun (46% of the distance at which the Earth orbits the Sun; slightly outside the orbit of the planet Mercury) and out to 1.17 AU (17% 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 February this year and the next predicted in August 2020. 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.

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Cinnamomum bladenense: A new species of Cinnamon from southern Belize.

Cinnamons, Cinnamomum spp., are tropical trees in the Laurel Family, Lauraceae, best known for their aromatic bark, which is widely used to flavour food. There are currently about 350 known species of Cinnamon tree, most of which are found in tropical Asia, though 47 species have been described from the tropical forests of Central and South America.

In a paper published in the journal PhytoKeys on 7 June 2017, Steven Brewer of the Belize Foundation for Research and Environmental Education, and Gail Stott of the Department of Plant Sciences at the University of Oxford, describe a new species of Cinnamon from the Bladen Nature Reserve in southern Belize.

The new species is named Cinnamomum bladenense, where ‘bladenense’ means ‘from Bladen’ in reference to the Bladen Nature Reserve (this reserve in turn takes its name from the Bladen River, though the ultimate derivation of the name is unknown). It is a tall canopy tree (unusual for a Cinnamon) reaching 25 m in height, with flowers unusually small for the genus. It has a straight, round, trunk supported by buttress roots, the bark is grey with a pinkish cast, which when damaged reveals a pinkish brown under-layer with a strong soapy odour, reminiscent of a bathroom cleaner. The leaves are waxy, 35-86 mm in length and 11-31 mm wide, flowers are brown-to-black, roughly 5 mm in length and born on leaf axils 40-80 mm in length and covered in grey hairs. 

Diagnostic vegetative characters of Cinnamomum bladenense. (A) Branch showing adaxial surface and variation of leaf sizes within branches. (B) Abaxial surface of leaves showing matte green laminae and prominent midvein and secondary venation. (C) Young twigs moderately and minutely sericeous with whitish buds. (D), (E) From the base of the same leaf lamina, respectively, adaxial surface of secondary vein axils not ampullous, abaxial surface of secondary veins barbellate and plane with the lamina surface. Steven Brewer in Brewer & Stott (2017).

The species is described from less than ten trees found growing on a pair of limestone ridges (an unusual location for a Cinnamon) south of the Bladen River. These locations are slightly upstream of the stretch where the river descends onto the coastal plain, and are on steep, well drained slopes in semi-evergreen forest. No further trees were found in the Bladen Nature Reserve, but similar environments are known to the southwest, close to the border with Guatemala, and to the northeast along the foothills of the Maya Mountains, as far as the southeastern portion of the Cockscomb Basin. For this reason the conservation status of Cinnamomum bladenense is unknown, though Brewer and Stott note that while the Bladen Nature Reserve is theoretically protected, it is prone to illegal logging and burning.

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Hundreds dead after mudslide in Sierra Leone.

Three hundred and twelve people, including about sixty children, have now been confirmed dead and it is thought that many more have yet to be found after a hillside collapse on the south slope of Sugar Loaf Mountain, to the south of Freetown, led to a river of mud washing through the town of Regent, on Monday 14 August 2017. The incident happened early in the morning, while many residents of the city were still sleeping, and has swept away hundreds of homes, many in informal settlements built illegally by migrants from the countryside in areas known to be prone to flooding. Several thousand people are thought to have been made homeless in the incident.

River of mud flowing through the town of Regent, Sierra Leone, following a hillside collapse on 14 August 2017.  AFP.

The incident happened following days of heavy rains associated with the West African rainy season. Landslides are a common problem after severe weather, 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.

 The approximate location of the 14 August 2017 Regent landslide. Google Maps.

West Africa has a distinct two season climatic cycle, with a cool dry season during the northern winter when prevalent winds blow from the Sahara to the northeast, and a warm rainy season during the northern summer when prevalent winds blow from the Atlantic Ocean to the southwest. These warm winds from the Atlantic are laden with moisture, which can be lost rapidly when the air encounters cooler conditions, such as when it is pushed up to higher altitudes by the mountains of the Futa Jallon in Guinea.

 Rainfall and prevalent winds during the West African dry and rainy seasons. Encyclopedia Britanica.

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