Sunday, 17 March 2019

Magnitude 5.5 Earthquake on Lombok triggers deadly landslide.

Two Malaysian tourists have been confirmed dead and at least 20 more have been injured, and several more are still missing, following a landslide at a waterfall on Lombok Island, Indonesia, popular with tourists, triggered by an Earthquake on Sunday 17 March 2019. The Earthquake was recorded by the United States Geological Survey as having a Magnitude of 5.5 and having occurred at a depth of 23.6 km, slightly before 2.10 pm local time (slightly before 7.10 am GMT), and was felt across the islands of Lombok and Bali. One of the dead has been named as Datin Tai Siew, the deputy executive editor-in-chief of Malaysian newspaper Sin Chew Daily.

Datin Tai Siew, the deputy executive editor-in-chief of the Chinese language Malasian newspaper Sin Chew daily, killed by an Earthquake-triggered landslide on Lombok on 17 March 2019. Bernama.

The Indo-Australian Plate, which underlies the Indian Ocean to the south of Java, Bali and Lombok, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies the islands and neighbouring Sumatra, along the Sunda Trench, passing under the islands, 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 Java and neighbouring islands.

 Subduction along the Sunda Trench beneath Java, Bali and Lombok. Earth Observatory of Singapore.

Meanwhile, to the north of Lombok and eastwards through the Lesser Sunda Islands, the Eurasian Plate is also being subducted beneath the islands, creating a separate microplate. the Timor Plate, with subduction beneath it to both the south and the north.

The subduction zones beneath the Timor Microplate. Hamson (2004).
  
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.

 The approximate location of the 17 March 2019 Lombok Earthquake. USGS,

See also...

https://sciencythoughts.blogspot.com/2018/08/magnitude-69-earthquake-beneath-lombok.htmlhttps://sciencythoughts.blogspot.com/2018/07/magnitude-64-earthquake-beneath.html
https://sciencythoughts.blogspot.com/2018/01/landslide-kills-man-on-lombok-island.htmlhttps://sciencythoughts.blogspot.com/2017/02/magnitude-46-earthquake-to-south-of.html
https://sciencythoughts.blogspot.com/2016/09/thousands-evacuated-following-eruption.htmlhttps://sciencythoughts.blogspot.com/2015/11/flights-cancelled-to-and-from-lombok.html
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Comet 69P/Taylor reaches perihelion.

Comet 69P/Taylor will reach its perihelion (the closest point on its orbit to the Sun) on Monday 18 March 2019, when it will be approximately 2.28 AU from the Sun (i.e. 228% of the distance between the Earth and the Sun, between the orbits of Mars and Jupiter). The comet will be in the constellation of Taurus seen from the Earth in the evening, though it will not be visible without a very good telescope.

The orbit and current position of Comet 69P/Taylor. In The Sky.

Comet 69P/Taylor was discovered on 24 November 1915 by Clement Taylor, an amateur astronomer based in Cape Town, South Africa. The designation 69P/Taylor implies that it is a Periodic Comet (comet which orbits the Sun in less than 200 years), that it was discovered by Taylor, and that it was the 69th comet discovered.

Comet 69P/Taylor, centre of field, imaged on 13 December 2004. Michael Jager & Gerald Rhemann/Seiichi Yoshida's Comet Page.

69P/Taylor has an orbital period of 2804 days (7.68 years) and a highly eccentric orbit tilted at an angle of 22.0° to the plain of the Solar System, that brings it from 2.28 AU from the Sun at perihelion (228% of the distance between the Earth and the Sun); to 5.50 AU from the Sun at aphelion (5.50 times as far from the Sun as the Earth or roughly the distance at which Jupiter orbits). As a comet with a period of less than 20 years with an orbit angled at less than 30° to the plane of the Solar System, 69P/Taylor is considered to be a Jupiter Family Comet.
 
See also...
 
https://sciencythoughts.blogspot.com/2018/12/looking-for-colour-changes-on-surface.htmlhttps://sciencythoughts.blogspot.com/2018/12/comet-38pstephan-oterma-makes-its.html
https://sciencythoughts.blogspot.com/2018/12/comet-46pwirtanen-approaches-earth.htmlhttps://sciencythoughts.blogspot.com/2018/07/comet-c2017-t3-atlas-makes-its-closest.html
https://sciencythoughts.blogspot.com/2018/06/comet-c2016-m1-panstarrs-makes-its.htmlhttps://sciencythoughts.blogspot.com/2018/05/comet-c2016-r2-panstarrs-reaches.html
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Flooding and landslides kill at least fifty in Papua Province, Indonesia.

At least fifty people, including a number of children, have died, with several hundred still missing ans fifty nine being treated in hospitals for a variety of serious injuries, with several thousands having been made homeless, following a series of landslips and floods around in the Sentani Subdistrict of Papua Province, Indonesia, on Saturday 16 March 2019. The worst of the flooding appears to have occurred after a landslip partially blocked the path of an already swollen river, causing it to burst its banks.

Rescue workers carrying the body of a flood victim in Sentani, Papua. Basarnas/AP.

The flooding and landslips have been linked to heavy rains in the area, which has been experiencing a particularly severe rainy season this year.  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. This problem has been made worse by the clearing of forests for palm oil production, the wholesale clearing of trees for timber (often illegally, due to the high value of tropical hardwoods on the international market), both of which lead to the loss of the trees which often stabilise soil on slopes, as well as an expanding population, which has led to people farming higher on hillslopes, in an area where soils tend to be volcanic in action and poorly consolidated (i.e. lack much cohesion), making them more prone to landslides.

 Residents of Sentani in a temporary shelter following flooding in the area. BNPB/EPA.

Papua has a tropical climate, with a Rainy Season related to the Northeast Monsoon that lasts from December to March, with each of those months typically receiving more than 250 mm of rain. Indonesia has two distinct Monsoon Seasons, with a Northeast Monsoon driven by winds from  the South China Sea that lasts from November to February and a Southwest Monsoon driven by winds from the southern Indian Ocean from March to October (this Southern Monsoon does not typically reach Flores, resulting in a dry season over these months). Such a double Monsoon Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest.  

 The winds that drive the Northeast and Southwest Monsoons in Southeast Asia. Mynewshub.
 
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.

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

See also...

https://sciencythoughts.blogspot.com/2016/08/magnitude-57-earthquake-in-papua.htmlhttps://sciencythoughts.blogspot.com/2013/05/another-worker-killed-in-fresh-grasberg.html
https://sciencythoughts.blogspot.com/2013/05/23-miners-still-trapped-after-cave-in.htmlhttps://sciencythoughts.blogspot.com/2013/04/magnitude-70-earthquake-under-west-papua.html
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Magnitude 6.3 Earthquake in Germán Jordán Province, Bolivia.

The United States Geological Survey recorded a Magnitude 6.3 Earthquake at a depth of 358.3 km in Germán Jordán Province, Bolivia, at about 11.15 pm local time on Thursday 14 March 2019 (about 3.15 am on Friday 15 March GMT). Quakes at this depth are seldom dangerous, but are often felt over a wide area, and this one was reportedly felt across much of western Bolivia. as well as southern Peru and northern Chile.

The approximate location of the 14 March 2019 Germán Jordán Earthquake. USGS.

Bolivia is located close to the west coast of South America, which is also the convergent margin between the Nazca and South American Plates. The Nazca Plate is being subducted beneath the South American Plate and is sinking beneath the South American Plate. This is not a smooth process, the rocks of the two plates continuously stick together then, as the pressure builds up, break apart again, causing Earthquakes. As the Nazca Plate sinks deeper it is partially melted by the friction and the heat of the Earth's interior. Some of the melted material then rises up through the overlying South American Plate as magma, fuelling the volcanoes of the Bolivian Andes. 

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.
 
See also...
 
https://sciencythoughts.blogspot.com/2019/02/bolivian-landslide-kills-at-least.htmlhttps://sciencythoughts.blogspot.com/2018/04/magnitude-68-earthquake-in-luis-calvo.html
https://sciencythoughts.blogspot.com/2013/10/magnitude-50-earthquake-in-southwest.html
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Saturday, 16 March 2019

Asteroid 2019 EW1 passes the Earth.

Asteroid 2019 EW1 passed by the Earth at a distance of about 611 260 km (1.59 times the average distance between the Earth and the Moon, or 0.41% of the distance between the Earth and the Sun), slightly after 2.05 am GMT on Monday 11 March 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 EW1 has an estimated equivalent diameter of 7-23 m (i.e. it is estimated that a spherical object with the same volume would be 7-23 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 37 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2019 EW1. JPL Small Body Database.

2019 EW1 was discovered on 9 March 2019 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2019 BU1 implies that it was the 46th asteroid (asteroid W1 - 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 W1 = 22 + 24 = 46) discovered in the first half of March 2019 (period 2019 E).

2019 EW1 has a 344 day orbital period, with an elliptical orbit tilted at an angle of 7.21° to the plain of the Solar System which takes in to 0.63 AU from the Sun (63% of the distance at which the Earth orbits the Sun, and slightly less than the distance at which Venus orbits the Sun) and out to 1.29 AU (29% 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 18 May lat year (2018) and the next predicted in February next year (2020). Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2019 EW1 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. This also means that the asteroid has occasional close encounters with the planet Venus, with the last calculated to have occurred in September 2013, and the next predicted for November 2027.

See also...

http://sciencythoughts.blogspot.com/2019/03/investigating-meteoroid-impact-on-moon.htmlhttp://sciencythoughts.blogspot.com/2019/03/looking-for-asteroids-in-2018-la-like.html
http://sciencythoughts.blogspot.com/2019/03/fireball-over-united-arab-emirates.htmlhttp://sciencythoughts.blogspot.com/2019/03/looking-for-source-of-heavy-nitrogen-in.html
http://sciencythoughts.blogspot.com/2019/03/asteroid-2019-db-passes-earth.htmlhttp://sciencythoughts.blogspot.com/2019/03/asteroid-2019-dp-passes-earth.html
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Warning issued after cliff collapse at West Bay, on England's Jurassic Coast.

The Jurassic Coast Trust and the Environment Agency have issued a warning for people to keep away from the East Cliffs at West Bay following a cliff collapse on Wednesday 13 March 2019. About a thousand tonnes of rock fell from the cliff onto the beach without any warning, narrowly missing several passers by, although fortunately nobody was hurt. The site was inspected shortly after by geologist Sam Scriven of the Jurassic Coast Trust, who has warned that the cliff remains unstable and further collapses are likely.

Rockfall on the beach beneath the East Cliffs at West Bay this week. Sam Rose/Jurassic Coast Trust/Dorset Echo.

The cliffs at East Bay are made up of two main layers, the Bridport Sands at the base, and the Inferior Oolite (limestone made up of egg-shaped particles) above. These cliffs are usually very stable, but in very wet conditions, such as those experienced by the UK this week, the sandstones can become waterlogged and lose their cohesion, causing collapses which undermine the limestones above. 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.

 The East Cliffs at West Bay, seen from Burton Bradstock. UK Fossils.

The beaches of Dorset are famed for their numerous Jurassic fossils, which attract many people to the area. These fossils are produced by erosion of the cliffs, and collected by both amateur enthusiasts and professional palaeontologists from the beaches below (direct excavation from the cliffs is strictly forbidden, due to the dangers of rockfalls). The beaches at West Bay are not usually considered among the better fossil collecting spots in the region, due to the stability of the cliffs, which means that new fossils arriving on the beach is a rarity. However, the Inferior Oolite is noted for its many well preserved Ammonite fossils, which can be found on the beaches after rockfalls such as the one that occurred this week. This is problematic for site managers with the Jurassic Coast Trust, as it means that people will often try to access the site immediately after rockfalls, in the hope of finding the best fossils before other collectors arrive, rather than waiting for the area to be declared safe.

Simple geological section of the cliffs at West Bay. Ian West/Geology of the Wessex Coast of Southern England/University of Southampton.

See also...

https://sciencythoughts.blogspot.com/2018/12/austaulius-haustrum-new-species-of.htmlhttps://sciencythoughts.blogspot.com/2014/06/a-metriorhynchid-crocodylomorph-tooth.html
https://sciencythoughts.blogspot.com/2013/08/a-pliosaur-from-jurassic-coast-of-dorset.htmlhttps://sciencythoughts.blogspot.com/2013/03/landslip-at-bowleaze-cove-dorset.html
https://sciencythoughts.blogspot.com/2012/08/earthquake-off-dorset-coast.htmlhttps://sciencythoughts.blogspot.com/2012/08/monmouth-beach-lyme-closed-due-to.html










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