Wednesday, 22 March 2017

Magnitude 5.5 Earthquake beneath southern Bali.

The United States Geological Survey recorded a Magnitude 5.5 Earthquake at a depth of 118.5 km about 2 km to the northwest of Banjar Pasekan on Bali in Indonesia at about 7.10 am on Wednesday 22 March 2017 local time (about 11.10 pm on Tuesday 21 March GMT) . The event was felt across most of Bali, Lombok and East Java, but there are no reports of any damage or injuries.

The approximate location of the 22 March 2017 Bali Earthquake. USGS.

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.

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.
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Tuesday, 21 March 2017

Contractor killed at Tasmanian mine.

A contractor at an iron-ore mine on the west coast of Tasmania, Australia, on Friday 17 March 2017. The worker, identified as Nathan Beesley, 32, from Devon in England is understood to have been scaling (removing small fragments of rock by hand) on a rock face at the Grange Resources-owned Savage River Mine, when he was struck by a piece of falling rock and fell to his death. He is survived by a wife and two young sons.

Nathan Beesley, left, killed at a mine on the west coast of Tasmania on 17 March 2017. Katie Beesley/BBC.

Mr Beesley, a former Sergeant in the Royal Marines, had moved to Australia in the hope of joining the Australian Defence Force, however the process had taken longer than he anticipated, and he had taken alternative work whole waiting for an interview. His wife has expressed concern as to the future of the family, as they are not yet permanent residents of Australia and may be obliged to leave in the absence of a breadwinner.

The incident is under investigation by WorkSafe Tasmania. This is the fourth fatality at a mine on the west coast of Tasmania since 2013.

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Monday, 20 March 2017

The March Equinox.

The March Equinox fell on 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 Sun at the planet's equinoxes and solstices. Astronomy Group/University of St Andrews.

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.

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Saturday, 18 March 2017

Fireball meteor over British Columbia and Washington.

Witnesses in southern British Colombia and western Washington State have reported seeing a bright fireball meteor at about 9.40 pm local time on Thursday 16 March 2017. The event is described as a meteor followed by a bright green flash, then a second yellow flash, and was witnessed between Victoria in the west and West Kelowna in the east.

The 16 March 2017 fireball meteor seen from Pitt Meadows in British Columbia. Tammy Kwan/CBC News.

A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry. Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. 
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Pirates release oil tanker seized off Somali coast.

An oil tanker and its eight crew members (all understood to be Sri Lankan nationals) that was seized by pirates in the Socotra Gap (between the Somali coast and the Yemeni island of Socotra) on Monday 13 March 2017 have been released without any ransom being paid, according to officials in Sri Lanka and Somalia. The United Arab Emirates-owned, Comoros-registered Aris 13 was hijacked while shipping a cargo of oil from Djibouti to the Somali capital Mogadishu, the first oil tanker attacked in the region since 2012. The hijackers contacted the European Union Naval Force (which co-ordinate anti-piracy efforts in the area) on Wednesday 15 March, demanding an undisclosed ransom for the release of the vessel and its crew, but decided to release the ship without ransom after an exchange of gunfire with the Puntland Maritime Police Force on Thursday, in which four people were injured, followed by negotiations with local elders. The pirates have stated that they were releasing the ship as it had been hired by Somali (rather than foreign) business interests.

The Aris 13, seized by pirates off the coast of Somalia on 13 March 2017. AP.

Piracy around the Horn of Africa was a major problem during the Somali Civil War, with over a thousand hostages taken between 2007 and 2012 (eight Iranian seamen are still thought to be being held somewhere in Somalia), with lucrative oil vessels being the most popular targets. However the decline of fighting in Somalia combined with the deployment of the European task force to the area appeared to have brought the problem under control.

However a growing food crisis in Somalia, caused by a drought associated with this years La Niña weather system, combined with a longer-standing dispute over foreign fishing vessels operating of the north coast of Somalia, many of which are licensed by the government of the semi-autonomous Puntland region (which views the licenses as a valuable source of hard currency), has led to a number of attacks on fishing boats (seen by local fishermen as stealing their Fish) in recent months, and it is feared that the 13 March attack may represent an escalation of this dispute.

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Magnitude 5.2 Earthquake in Cundinamarca Department, Colombia.

The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of 10.3 km approximately 17 km to the northwest of the town of Ulala in Cundinamarca Department, Colombia, at before 10.40 am local time (slightly before 3.40 pm GMT) on Thursday 16 March 2017. There are no reports of any damage or casualties associated with this event, but people have reported feeling the event across much of Colombia as well as in western Guiana 
The approximate location of the 16 March 2017 Cundinamarca Earthquake. USGS.
Colombia is on the west coast of South America and the western margin of the South American Plate, close to where the Nazca Plate, which underlies part of the east Pacific, is being subducted along the Peru-Chile Trench. The Nazca Plate passes under the South American Plate as it sinks into the Earth, this is not a smooth process and the plates repeatedly stick together then break apart as the pressure builds up, causing Earthquakes. As the Nazca Plate sinks further it is partially melted by the friction and the heat of the Earth's interior. Some of this melted material then rises through the overlying South American Plate, fuelling the volcanoes of Colombia and neighbouring countries.

The subduction of the Nazca Plate beneath the South American Plate, and how it causes Earthquakes and volcanoes. SIO SEARCH.
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.
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Friday, 17 March 2017

Eight injured following phraetic eruption on Mount Etna.

Eight people, including members of a BBC film crew, three vulcanologists from the Istituto Nazionale di Geofisica e Vulcanologia and several tourists and their guide have been injured following a phraetic eruption (explosion caused by water coming into contact with hot lava and vapourising) on Mount Etna on Thursday 16 March 2017. The BBC team, lead by science journalist Rebecca Morelle, were making a program about advances in volcano monitoring, featuring the work of the Italian scientists, when a lavs flow encountered a snowfield, triggering an explosion of steam that showered them with lava and chunks of rock. Most of the party escaped with cuts and burns, though several had to be taken off the mountain by mountain rescue teams.

A member of the BBC team with a jacket burned through by hot rock. Rebecca Morelle/BBC.

Etna first erupted about half a million years ago, beneath the sea off the east coast of Sicily, and has been going strong ever since. It now stands 3330 m above sea level, and covers 1200 km³. It is responsible for fertile soils across eastern Sicily. Records of eruptions on Etna go back to 1500 BC. It is Europe's second largest volcano, after Teide in the Canary Islands, and is one of the most active volcanoes in the world.

 Members of the BBC team fleeing the explosion. Rebecca Morelle/BBC.

Despite all this Etna has only ever caused 77 recorded deaths (the most recent being two tourists caught in a summit explosion in 1987) and relatively little destruction. In 1928 it destroyed the village of Mascali on its northeastern flank, though there were no reported casualties, the village being slowly overrun by a lava flow. In 1669 a much larger lava flow destroyed at least 10 villages, reaching the walls of the city of Catania, 40 km to the south, but again without loss of life. In 122 BC a heavy ash fall covered much of the region, causing several buildings to collapse in Catania. The destruction was deemed so severe by the Roman authorities that they granted the city a 10 year tax holiday. In about 6000 BC a landslide on the eastern flank of the volcano is thought to have caused a tsunami that caused destruction around much of the eastern Mediterranean.  

  The location of Mount Etna. Google Maps.

Etna is located on the border of the African and European Plates, specifically where Africa is being subducted beneath the European Plate. As it is drawn into the Earth's interior material from the African Plate melts, and the lighter portions rise up through the overlying European Plate, causing a number of volcanoes including Etna and Vesuvius. 

Map showing the tectonic plates underlying Italy and southern Europe, and the location of the l'Aquila Earthquake. Napoli Unplugged.

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