Saturday 30 November 2019

Tunnel collapse kills at least four in Tunnan Province, China.

Four people have been confirmed dead and another eight are missing following the collapse of a road tunnel during construction in the city of Lincang in Yunnan Province, China on Tuesday 26 November 2019.  The event happened at about 6.00 pm local time, with part of the tunnel giving way and water and soft sediment rushing into the tunnel. One person was pulled out of the tunnel alive, who is now in hospital and described as being in a stable condition.

Rescue workers at the scene of a tunnel collapse in Lincang City, China, on 26 November 2019. Yan Hua/Xinhua.

The precise cause of the collapse is unclear, but it is likely that the tunnellers encountered a pocket of water or water-logged sediment during excavations. Photographs from the scene show significant amounts of grey mud in the tunnel, which is likely to be a sign of calcareous deposits, and local reports have spoken of ongoing flooding and weathered geology hampering rescue operations. This is likely to be indicative of a karst terrain, where limestone is both soft and porous, and water from the surface sinks into it freely, permeating through the rock and excavating caves through which the water flows. If the tunnel encountered or came close to a water-filled cave in such a terrain it is likely that the rock would collapse into the tunnel, leading to a flood.

A diagrammatic representation of how sinkholes and caves form in karst landscapes. Wisconsin Geological and Natural History Survey.

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Friday 29 November 2019

Sinkhole swallows car in Kuala Lumpur, Malaysia.

A car was trapped in a sinkhole in Kuala Lumpur on Sunday 24 November 2019.  The incident happened at about 11.35 pm local time, in the Kampung Attap area of the city, when part of the road collapsed beneath the front of the moving car, trapping both the vehicle and the forty-two-year old woman driving it. The car was eventually winched out of the hole, apparently only having suffered minor damage to its front bumper.

Car trapped in a sinkhole in Kuala Lumpur, Malaysia, on 24 November 2019. Adinda Qilla Apmkl/Facebook.

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.

 Workers inspecting a sinkhole in Kuala Lumpur, Malaysia, before repairs can be attempted. BBX Press.

On this occasion geologist Nor Bakhiah Baharim of the Universiti Malaysia Terengganu has suggested that the hope appeared due to the erosion of limestone beneath the road, a substrate that underlies much of the city, and suggested that sinkholes may be a problem in the area if buried water pipes leak or burst, and that extra care should be taken in installing such pipes in areas built on limestone.

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Magnitude 5.2 Earthquake in Guangxi Province, China.

The China Earthquake Networks Center recorded a Magnitude 5.2 Earthquake at a depth of 10 km in Jingxi County in Guangxi Province, China, slightly before 9.20 am local time (slightly before 9.20 am GMT) on Monday 25 November 2019. The Earthquake triggered a number of landslides in the area, resulting in one person being killed and four more injured, and was felt across Guangxi Province and northern Vietnam.

A landslide in the town of Hurun in Jingxi County, Guangxi, triggered by an Earthquake on 25 November 2019. Xinhau

Earthquakes are common in west and southwest China, where the Eurasian Plate is being compressed by the impact of the Indian Plate from the south, but much less common in the east and centre of the country. However southeastern China is in fact dominated by a series of tectonic blocks, annealed onto the Eurasian Plate during the Triassic. Guangxi Province is located on the South China Block, which is being pushed to the southeast by the motion of the Tibetan Block to the northwest and North China Block to the northeast.

 Tectonic map of Asia, showing relationships between the India–Asia collision, escape of Indonesian and South China blocks seaward, and extension from Siberia to the Pacific margin. (Note also the opening of back-arc basins including the Sea of Japan and the South China Sea, and extension in the Bohai Basin and eastern part of the NCC.) The North China Craton is also strongly influenced by Pacific and palaeo-Pacific subduction, perhaps also inducing extension in the eastern NCC. The palaeo Pacific and Pacific subduction zones developed in the Mesozoic, and also contributed to the hydration of the subcontinental lithospheric mantle beneath the NCC. Kusky et al. (2007).

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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Thursday 28 November 2019

Egyptologists uncover a trove of new animal mummies at Saqqara.

The Egyptian Ministry of Antiquities has revealed the discovery of a collection of new animal mummies and related artifacts discovered at the Saqqara Necropolis, to the south of Cairo, this year. The finds include about 100 statues, mostly of Cats, as well as Birds, Bulls, Scarab Beetles, a Mongoose, and several Gods and Goddesses. A large number of animal mummies were also uncovered, including Cats, Cobras, Crocodiles, Scarab Beetles, and three large Felids, two of which have been identified as Lion cubs about a metre in length, and the other three of which are still yet to be identified. This last find is particularly interesting as only one previous Big Cat has been found mummified in Egypt, a partial Lion also found at Saqqara in 2004.

A mummified Lion cub from the Saqqara Necropolis. Egyptian Ministry of Antiquities.

The material also includes 73 statues of the God Osiris, eleven statues of the Lion-headed Goddess Sekhmet, six statues of Ptah-Soker, who was widely venerated by craftsmen, and a statue of the Goddess Neith, who was worshipped as the creator of all things in the city of Sais, capitol of Egypt during the 26th Dynasty (roughly 610-664 BC). The name of the 26th Dynasty Pharoah Psamtik I was also found on at least one artifact, further supporting the idea that these finds came from that period.

Cat mummies from the Saqqara Necropolis. Egyptian Ministry of Antiquities.

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Wednesday 27 November 2019

Avalanche injured two skiers in the French Alps.

Two skiers have been injured in an avalanche at the Valfréjus ski resort in the Savoie Department of France on Saturday 23 November 2019. The incident happened on the Col ski piste above the Arrondaz Plateau at an altitude of about 2300 m above sealevel. The injured skiers are reported to have been part of a party of three pensioners from Lyon, plus a guide in their 30s. They were dug out by friends and airlifted to a hospital in Saint-Jean-de-Maurienne. The incident is reported to have been caused by a layer of loose fresh snow forming above a more compacted layer of older snow, with little adhesion between the two layers, so that the upper layer gave way when disturbed.

The approximate location of the 23 November 2019 Col d'Arrondaz avalanche. Google Maps.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

 Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

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Flooding and landslides kill at least seventy two in West Pokot County, Kenya.

At least seventy two people have died in a series of flash floods and landslides in West Pokot County, Kenya, following heavy rains that began in the area on Friday 22 November 2019. The majority of the deaths are reported to have happened in a series of mudslides triggered by the rains. 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. Five people are reported to have died when their car was swept away after a river burst its banks; two pedestrians were also killed in the same event. Another eleven people were killed in a house that was buried by a landslide, while seventeen people were killed in a mudslide in the village of Takmal, and twelve more in landslips in the villages of Parua and Tapach. Fatalities due to similar events have also been reported in other parts of Kenya, Somalia, Ethiopian, South Sudan, Sudan, Tanzania, the Democratic Republic of Congo, the Republic of Congo and the Central African Republic.

Debris left by a flash flood in West Pokot County, Kenya. AP.

Like seasonally dry areas, Kenya is particularly prone to flash floods. This stems from two causes; firstly the arid climate prevents the development of a thick soil layer which would be expected in less dry areas, so that in much of the area (non-porous) bedrock is either exposed or close to the surface, and secondly the hot climate leads to heavy evaporation from nearby seas and oceans, so that if the wind changes direction and brings water-laden air to the area, it brings a lot of precipitation with it. This combination of heavy rainfall and low ground absorbency leads to large amounts of water at the surface, typically moving downhill at some speed.

The incident occurred after about a month of heavy rains, in one of the area's two annual rainy seasons. This two rainy seasons per year pattern is typical in equatorial countries, with rainy seasons around the equinoxes and dry seasons around the solstices. Upland areas of Kenya have always been prone to landslides, but the problem has become worse in recent years as a rising population has led to more agriculture on hill-slopes, in many areas replacing open woodland where tree roots served to stabilise slopes, and also to more people living in harms ways.

 The aftermath of a mudslide in the village of Parua in West Pokot County on 23 November 2019. Reuters.

The rains this year are thought to have been made worse by the development of a meteorological phenomenon called a Negative Indian Ocean Dipole. Indian Ocean Dipole Phases are similar to the El Niño/La Niña climatic oscillation that affect the Pacific Ocean. Under normal circumstances equatorial waters off the east coast of Africa and west coast of Indonesia are roughly similar in temperature, however during a Negative Indian Ocean Dipole Phase the waters off the coast of Indonesia become significantly warmer. As the prevailing currents in the area flow west to east, this warm water is then pushed onto the shallower continental shelf of north Australia, where it warms the air over the sea more rapidly, leading to increased evaporation (which fuels rain) and a drop in air pressure over the east Indian Ocean and west Pacific. This in turn drives air currents over the Indian Ocean to flow more strongly west to east, leading to higher rates of  cooling off the coast of Africa (where more water is drawn up from the cool sea depths) and more warming off the coast of Indonesia, fuelling a feedback cycle that tends to remain through the winter season in any year when it forms. This leads to a particularly wet winter across much of Australia, as well as a potentially damaging heatwave in the north, while much of East Africa is at risk of drought (during a Positive Indian Ocean Dipole Phase the reverse happens, with drought in Australia and flooding in East Africa).

 Areas of warming and cooling and air flow during a Negative Indian Ocean Dipole Phase. Australian Bureau of Meteorology.

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Tuesday 26 November 2019

Magnitude 6.4 Earthquake in central Albania kills at least 20 people.

The United States Geological Survey recorded a Magnitude 6.4 Earthquake at a depth of about 20.0 km, roughly 12 km to the southwest of the town of  Mamurras in western Albania, slightly before 3.55 am local time (slightly before 2.55 am GMT) on Tuesday 26 November 2019. The quake has caused widespread damage in Albania, with many collapsed buildings and at least twenty fatalities, and over six hundred people are reported to have been injured. The event was felt across the Balkan Peninsula and Italy. The worst casualties occurred in the town of Durrës, where at least six buildings collapsed, including an apartment block.

Damaged buildings in the town of Durrës in western Albania, following a Magnitude 6.4 Earthquake on Tuesday 26 November 2019. Hektor Pustina/AP.

The coastal region of Albania, and the other states of the western Balkan Peninsula, forms the eastern margin of the Adriatic Plate, a piece of the African Plate that has broken away and is now wedged into the southern part of the Eurasian Plate. This is being squeezed by the impact of Africa into Europe from the south, which is pushing western Italy, which sits on the Eurasian Plate, to the east, and Greece and Turkey, which sit on the Aegean and Anatolian Plates, to the west. This squeezing leads to uplift around the margins of the Adriatic Plate, in the Apennines Mountain Range of central Italy and the mountain ranges of the west Balkan Peninsula.

  Outline map showing the approximate positions of the Eurasian (EU), Adriatic (AD) and African (AF) Plates. Di Bucci & Mazzuli (2003).

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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