Saturday, 24 February 2018

Landslide kills at least seven in Central Java.

Seven people are known to have died and at least thirteen more are missing following a landslide that hit the village of Pasir Panjang in the Brebes District of Central Java, Indonesia, on Thursday 22 February 2018. Several more people needed hospital treatment after the event, which has displaced about 250 people from their homes. The incident is reported to have occurred when a soil slope above the village after about two weeks of heavy rain in the area. 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.

Damage to buildings in the village of Pasir Panjang in Central Java, following the 22 February 2018 landslip. Oky Lukmansyah/Antara Foto/Reuters.

Landslides are a common problem in Java, particularly during the Northeast Monsoon, which lasts from November to February, with peak rainfall in January and February, and can result in an annual rainfall of around of 4000 mm in parts of Central Java. This problem has been made worse as expanding populations 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.

The approximate location of the 22 February 2018 Pasir Pajang landslide. Google Maps.

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.

Java 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. 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.

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Friday, 23 February 2018

Magnitude 5.0 Earthquake beneath the Ionian Sea.

The United States Geological Survey recorded a Magnitude 5.0 Earthquake at a depth of 16.7 km, in beneath the Ionian Sea to the west of the island of Zakinthos, slightly before 1.45 am local time on Thursday 22 February 2018 (slightly before 11.45 pm on Wednesday 21 February GMT) . No damage or injuries have been reported following this event, but people have reported feeling the event on the islands of Zakinths and Ionia Nisea.

The approximate location of the 22 February 2018 Ionian Sea Earthquake. USGS.

The Ionian Sea overlies the boundary between the Aegean Sea Plate, which underlies southern Greece, and the African Plate, which underlies most of the Mediterranean. The African Plate is moving northward relative to the Aegean Sea Plate, and is being subducted beneath it along the Hellenic Trench, which runs from the Ionian Sea to the south and west of the Peloponnese and then to the south of Crete. This is not a smooth process, as the plates frequently stick together then break apart once the pressure has built up sufficiently, leading to (fairly frequent) Earthquakes.
The extent of the Hellenic Trench. Istituto Nazionale di Geofisica eVulcanologia.
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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Wednesday, 21 February 2018

Saltwater Crocodile kills man in Philippines.

A man has died after being attacked by a Saltwater Crocodile, Crocodylus porosus. on Balabac Island in the Philippines on Monday 19 February 2018. The man, identified as Rebente Ladja, 37, was reported missing when he failed to return home after setting traps for Crabs in a Mangrove Forest near his home. A search party later found his remains close to a large Saltwater Crocodile, which is presumed to have killed and partially eaten him.

A Saltwater Crocodile, Crocodylus porosus. Molly Ebersold/Wikimedia Commons.

This is the latest in a string of Crocodile attacks in the region, with five recorded attacks on Balabac Island since 2012, including a 12-year-old niece of Mr Ladja who is presumed dead after being dragged into the water by a Crocodile last year and never recovered.

The approximate location of the 19 February 2018 Balabac Crocodile attack. Google Maps.

Crocodile attacks on Humans are relatively rare, but they are opportunistic ambush predators and will potentially attack anything going close to the water. Saltwater Crocodiles have a particularly poor reputation for such behaviour, being the largest species of Crocodile and notoriously aggressive. These Crocodiles are one of the few Crocodile species not considered vulnerable to extinction, being found from India to Australia  and inhabiting many areas that Humans shun, such as Mangrove forests and islands without fresh water.

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Idaho man killed in avalanche.

A man has died in an avalanche in Swan Valley to the east of Palisades Reservoir, in Bonneville County, Idaho, on Tuesday 20 February 2018. Troy Leishman, 47, from Idaho Falls was snowmobiling with a group of friends when he was hit by the avalanche slightly after 4.00 pm local time. He was quickly located and dug out by his companions, but died at the scene of the incident.

The approximate location of the 20 February 2018 Swan Valley 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.

Northwestern North America have seen a number of avalanche related incidents this winter, largely due to high levels of snowfall. This is, in turn caused by warmer conditions over the Pacific, which leads to higher rates of evaporation over the ocean, and therefore higher rates of precipitation over North America, which falls as snow in cooler upland regions. There are further concerns that as the climate warms in the coming months, the thawing of this snow will lead to further dangerous avalanches.

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Worker killed in accident on oil rig in Gulf of Mexico.

A worker on an oil rig in the Gulf of Mexico was has died after an accident in the West Cameron 215 Block off the coast of Louisiana. The as yet unidentified worker was injured while replacing fire-suppression equipment, at about 10.30 am, local time, on Saturday 17 February 2018, and subsequently died of those injuries on Tuesday 20 February. There are not thought to have been any other injuries in the incident, nor has any oil or other substance been released into the environment on the platform, which is operated by Energy Resource Technology, a Texas-based subsidiary of Talos Energy. The incident is being investigated by the Bureau of Safety and Environmental Enforcement.

The approximate location of the Energy Resource Technology operated platform where a worker died on 20 February 2018. Bureau of Safety and Environmental Enforcement.

Energy Resource Technology last had a fatality on one of their platforms in October 2013, though the company was fined $4.2 million for breaches of offshore safety and environmental regulations in 2016, and placed on three years probation for felony charges relating to those breaches. Oil companies operating in the Gulf of Mexico are currently bound by strict environmental and safety regulations introduced in the wake of the Deepwater Horizon explosion, which killed eleven workers and led to a major environmental disaster. Incoming president Donald Trump promised to cut many of these regulations before his inauguration in January 2017, though he has yet to take any such action.

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Tuesday, 20 February 2018

Cyclone Gita reaches New Zealand.

Cyclone Gita made landfall on South Island, New Zealand, on Tuesday 20 February 2018, bringing flooding and high winds to the area around Christchurch in the Canterbury Region. There are no reports of any casualties associated with the storm in New Zealand at this time, though it has caused flight cancellations and several people have had to be rescued from floods. 

Debris on a swollen river near Bainham in the Tasman Region of South Island. Reuters.

Cyclone Gita first formed to the southeast of the Solomon Islands in the first week of February 2018. It passed to the south of Samoa and American Samoa between 8 and 11 February, causing flooding in both groups of islands, and wind damage in parts of American Samoa. The storm passed directly over Tonga on 12 February, causing extensive damage, to the islands' infrastructure, damaging over a thousand buildings, and totally destroying over a hundred, including the nation's parliament building. One person is known to have died in FuaŹ»amotu on Tongatapu (the largest island of Tonga and seat of the national government), with at least 30 more being injured, three of them seriously. After Tonga Cyclone Gita passed to the south of Fiji on 13 February, again causing flooding and wind damage, but this time no reported casualties.

Storm damage on Tonga following the passage of Cyclone Gita. John Pulu/AFP.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.
The passage of Cyclone Gita till 6.00 pm GMT on Monday 19 February 2018  (thick line) with its predicted future path (thin line, circles represent the margin of error on the predictions). Colours indicate the strength of the storm. Tropical Storm Risk.
The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides, which are 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.
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Eruption on Mount Sinabung, Sumatra, leads to evacuations and flight cancelations.

Flights have been cancelled and thousands of people have been evacuated after Mount Sinabung, a 2460 m stratovolcano (cone shaped volcano made up of layers of ash and lava) in North Sumatra, Indonesia, erupted suddenly at about 9.30 am on Monday 19 February 2018, producing a column of ash estimated to be over 7250 m high, accompanied by falling ash and even rockfalls in local communities. Local authorities have responded by evacuating communities within 7 km and cancelling flights over North Sumatra.

Ash column over Mount Sinabung on 19 February 2018. Maz Yons/Antara Foto/Reuters.

Sinabung is considered to be a potentially very dangerous volcano, as a large number of people live in its immediate vicinity. The last major eruption prior to the twenty-first century happened in about 1600, with small eruptions occurring in 1889 and 1912. However the volcano returned to life in late August 2010, erupting throughout September and causing about 12 000 people to flee their homes, and has been erupting intermittently ever since.

The location of Mount Sinabung. Google Maps.

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

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

The two plates are not directly impacting one-another, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

 The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

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