Monday, 20 February 2017

Eruption on Mount Krakatau.

The Middle InfraRed Observation of Volcanic Activity (MIROVA) monitoring system, which uses data from the Moderate-Resolution Imaging Spectroradiometer (MODIS) system on the Terra (EOS AM) and Aqua (EOS PM) satellites detected a thermal anomaly on Mount Krakatau, a volcanic island located in the Sunda Strait between Sumatra and Java, that famously exploded in 1883, killing over 36 000 people (possibly over 120 000), largely through a series of tsunamis, on Saturday 18 February 2017 suggesting a new bout of activity was staring on the island. On Monday 20 February a witness in the region contacted the Volcano Discovery website, confirming having witnessed volcanic activity on the 19th.

Eruptive activity on Mount Krakatau on 19 February 2017. Volcano Discovery.

Krakatau is located to the north of the Sunda Trench, along which the Australian Plate is being subducted beneath the Sunda Plate, on which the island sits. As the Australian Plate is subducted it is partially melted by the friction and the heat of the planet's interior. Some of this melted material then rises through the overlying Sunda Plate, fuelling Krakatau and the volcanoes of Sumatra and Java.

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

See also...
 
http://sciencythoughts.blogspot.co.uk/2017/01/magnitude-57-earthquake-in-north-sumatra.htmlhttp://sciencythoughts.blogspot.co.uk/2016/12/magnitude-65-earthquake-on-north-coast.html

http://sciencythoughts.blogspot.co.uk/2016/07/magnitude-51-earthquake-beneath-west.htmlhttp://sciencythoughts.blogspot.co.uk/2016/06/flooding-and-landslides-kill-forty.html
http://sciencythoughts.blogspot.co.uk/2016/05/pyroclastic-flow-kills-at-least-seven.htmlhttp://sciencythoughts.blogspot.co.uk/2016/05/seventeen-students-confirmed-dead-after.html
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Two Earthquakes in North Lincolnshire.

The British Geological Survey recorded a Magnitude 1.5 Earthquake at a depth of 16 km, about 10 km to the southeast of the town of Grimsby in north Lincolnshire, slightly after 5.30 am GMT on Friday 17 February 2017. This was followed by a second quake with a Magnitude of 1.3 at roughly the same location about 6.5 minutes later. These quakes were not large enough to have caused any damage or injuries, but may have been felt locally.
 
The approximate location of the 17 February 2017 Lincolnshire Earthquakes. 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.

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.
 
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 the first 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, and if you felt the second quake (or did not) then you can report it here.
 
See also...
 
http://sciencythoughts.blogspot.co.uk/2016/05/magnitude-13-earthquake-in-lincolnshire.html
http://sciencythoughts.blogspot.co.uk/2017/01/magnitude-38-earthquake-beneath.html
 
http://sciencythoughts.blogspot.co.uk/2016/02/nottinghamshire-sinkhole-traps-car.html
http://sciencythoughts.blogspot.co.uk/2016/04/magnitude-14-earthquake-near-barton.html
http://sciencythoughts.blogspot.co.uk/2015/09/magnitude-28-earthquake-in-rutland.html
http://sciencythoughts.blogspot.co.uk/2015/11/series-of-earthquakes-in-north.html

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Sunday, 19 February 2017

Sinkhole swallows two cars in Studio City, Los Angeles.

A sinkhole that opened up in the Studio City distrct of Los Angelese, California, swallowed two cars on Friday 17 February 2017. The hole, which is described as being about six meters across, engulphed a car and its female driver as it opened. The driver of this vehicle was able to escape from the hole with the help of firefighters, but shortely after the hole expanded, swallowing a second vehicle.

Arial view of the 17 February 2017 Studio City sinkhole. ABC7News.

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 2017 February 2017 Studio City sinkhole. Google Maps.

On this occassion the sinkhole has been linked to the exceptional rainfall falling across California this week, which is thought to have burst a sewer beneath the road, then washed away the sediment around it until the road collapsed.

California has been battered by a succession of Pacific storms this year, bringing widespread flooding and triggering a number of landslip and subsidence events. This is due to exceptionally high temperatures over the Pacific Ocean off the coast of the state this year caused by a La Niña weather system over the southern Pacific. This meant that the dam was already filled to capacity and regularly using the spillways to remove water when the damage was discovered, with another major series of storms due to start ariving later this week.

The La Niña weather system is the opposite of the El Niño weather system, in which unusually cold surface temperatures spread across the equatorial Pacific from the upwelling zone on the South American coast. This traps warm water from the western Pacific, preventing it from spreading east and warming the central Pacific. This leads to lower evaporation over the (cooler) east Pacific, leading to low rainfall on the west coast of South America, and higher evaporation over the (warmer) west Pacific, leading to higher rainfall over East and Southeast Asia and northern Australia.
 
The effects of a La Niña weather system in December-February. NOAA.
 
This also leads to a breakdown in surface circulation in the North Pacific, which generally rotates clockwise, so that the same body of water stays off the coast of California, where it is constantly warmed by the Sun, leading to high levels of evaporation and onshore winds that bring high rainfall and flood events to the state.
 
The effect of the La Niña weather system on the weather of North America. NOAA.
 
See also...

http://sciencythoughts.blogspot.co.uk/2016/10/magnitude-37-earthquake-in-san.htmlhttp://sciencythoughts.blogspot.co.uk/2016/10/magnitude-29-earthquake-in-orange.html
http://sciencythoughts.blogspot.co.uk/2016/07/sewage-spill-closes-long-beech.htmlhttp://sciencythoughts.blogspot.co.uk/2015/11/magnitude-35-qrthquake-beneath-northern.html
http://sciencythoughts.blogspot.co.uk/2015/10/flash-flooding-brings-chaos-to-south.htmlhttp://sciencythoughts.blogspot.co.uk/2015/06/magnitude-34-earthquake-hits-los-angeles.html
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Asteroid 2017 CP32 passes the Earth.

Asteroid 2017 CP32 passed by the Earth at a distance of about 918 800 km (2.39 times the average distance between the Earth and the Moon, or 0.61% of the distance between the Earth and the Sun), slightly before 5.35 am GMT on Sunday 12 February 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a genuine threat. 2017 CP32 has an estimated equivalent diameter of 31-99 m (i.e. it is estimated that a spherical object with the same volume would be 31-99 m in diameter), and an object towards the upper end of this range 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 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater over a kilometre in diameter and devastation on a global scale, as well as climatic effects that would last for years.

The calculated orbit of 2017 CP32. Minor Planet Center.

2017 CP32 was discovered on 15 February 2017 (three days after its closest approach to the Earth) by the Asteroid Terrestrial-impact Last Alert System (ATLAS) operated by the Institute of Astronomy of the University of Hawaii on Mount Haleakala in Hawaii. The designation 2017 CP32 implies that it was the 815th asteroid (asteroid P32) discovered in the first half of February 2017 (period 2017 C). 

2017 CP32 has a 282 day orbital period, with an elliptical orbit tilted at an angle of 17.0° 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; inside the orbit of the planet Venus) and out to 1.05 AU (5% 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 March 2014 and the next predicted in July this year. 2017 CP32  also has frequent close encounters with the planet Venus, with the last though to have occurred in July 2017 next predicted for December 2022. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2017 CP32 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
 
See also...
 
http://sciencythoughts.blogspot.co.uk/2017/02/looking-for-pieces-of-piecki-meteor.htmlhttp://sciencythoughts.blogspot.co.uk/2017/02/asteroid-2017-bq6-approaches-earth.html
http://sciencythoughts.blogspot.co.uk/2017/02/asteroid-2017-bg30-passes-earth.htmlhttp://sciencythoughts.blogspot.co.uk/2017/02/comet-45phonda-mrkos-pajdusakova.html
http://sciencythoughts.blogspot.co.uk/2017/02/fireball-over-american-mdwest.htmlhttp://sciencythoughts.blogspot.co.uk/2017/02/asteroid-2017-bh30-passes-earth.html

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