Fire and smoke

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EPA

Some of the images coming out of Mt Agung, the volcano in Bali which could be on the brink of a major eruption, have been spectacular. But the pictures also tell the story of what is going on inside, as volcanologist Janine Krippner explains.

Over the last two months Mt Agung has seen increased seismicity. This is the increased fracturing of rocks inside the volcano as magma, a volatile mixture of molten rocks, fluids and gases, moves from deep within the earth right up to the top.

In the past week we have seen thick plumes of steam and ash being belched out, as well as lava glowing at the surface of the crater, and flowing rivers of cold mud down river valleys.

Steam rising up

In most of the first pictures of the mountain two months ago, you wouldn’t have been able to tell there was an eruption brewing. That information came to us from the data within the mountain that detected its increased seismicity – and from tremors that began shaking the area.

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BAY ISMOYO

The most you would have seen is steam rising up, which was simply the water inside the volcano heating up and coming out of its surface. The mix of volcanic ash and lava that make up the mountain is like a sponge – and in rainy Indonesia the water soaks onto it and is held there until it gets heated up.

Since then it has been relatively quiet and this is typical for a volcano. These fluctuations in activity are what makes it so hard to predict.

Dense plumes of ash

The volcano first began belching thick ash and steam last Tuesday, its first eruption in more than 50 years.

This was a phreatic eruption – the expulsion of pressurised steam from inside the volcano because the magma within is heating up water. This can lead to a build-up of pressure which causes an explosion blasting rock and bits of the crater into tiny pieces of ash.

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AFP

The magma has been moving up from inside and it’s breaking rock as it goes along. As the magma moves up, water inside the volcano heats up, steam builds up pressure and it gets to a point where the rock just can’t hold it back any more. That is what we are seeing now.

So the magma has moved so high up the volcano there was not enough rock to hold it back, so it is being blasted into tiny pieces of ash and being spread about. Rocks, glass and crystal are flying out of the volcano.

If the eruption columns or plumes of ash are going straight up regardless of wind, it means the velocity is very high. The speed at which it comes out and the amount of ash determines how high a plume can get.

In the 1963 eruption of Mt Agung, eruptions reached as high as 26km (16 miles) above sea level.

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Reuters

At volcanoes like Agung, the magma can travel 5-15km to the surface from deep within the earth leading to an eruption.

The orange glow of the crater

At night, the orange glow at the surface of the crater is simply incandescence because it is just so hot. The magma is at the surface, and as it reaches the surface it becomes known as lava.

One of the reason the authorities increased the alert level to four is because the magma is getting higher and higher – and these images show exactly how high it is now.

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EPA

The volcano at sunrise

But the magma is not responsible for the spectacular images of pink and orange hues in the gas at dawn. That is simply the sunrise being reflected by the ash plume – the sun’s rays hitting the volcanic ash.

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Reuters

Different shades of ash

You can also learn a lot from the different shades of ash that rise up from the surface of a volcano. It’s possible that pictures showing two distinct ash colours could point to two vents in the crater – one that is producing more ash and another that is producing more steam.

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EPA

In the 1963 eruption of Mt Agung some researchers thought that it was possible there were two vents.

Dangerous rivers of mud and debris

The very latest images out of Bali point to a new development, which are volcanic mud flows – or lahars. The ash and rock depositing around the volcano when combined with rain can create dangerous fast-flowing rivers with the consistency of water up to wet concrete, and that can move and raise the river level very quickly.

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BNPB

It is not just water, they can carry debris such as boulders and trees and at the moment are something authorities are moving swiftly to warn residents about.

Janine Krippner is a volcanologist in Pittsburgh, USA.

Article source: http://www.bbc.co.uk/news/world-asia-42133502

Fruit jewellery, sugar dolls

A selection of the best photos from across Africa and of Africans elsewhere in the world this week.

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Reuters

Dancers perform on the streets of Ivory Coast’s commercial capital, Abidjan, as the Europe-Africa summit opens on Thursday. ”Investing in youth” was to be the focus of the event, but it has instead been dominated by talk of the migrant crisis.

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Reuters

Six-year-old Habiba hugs her toy dolls made of sugar, known as Aroset El Moulid (Bride of Mawlid) on Friday in Tanta, north of Egypt’s capital, Cairo. The figurines are made each year for the Mawlid festival which marks the Prophet Muhammad’s birthday.

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On Sunday, Miss South Africa, Demi-Leigh Nel-Peters, won the Miss Universe title at a ceremony in Las Vegas, US. But it was Miss Jamaica who won praise on social media for wearing her natural hair at the beauty pageant, with one Twitter user saying: “Not only did she represent Jamaica she also represented all the black women in the world, unapologetically rocking her beautiful afro”.

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British-Ghanaian grime artist Stormzy was the big winner at this year’s Mobo awards. He performed live at Wednesday’s event before walking away with three gongs – for best male act, best grime act and best album.

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Would-be stars perform on Saturday at the Bidi bidi refugee camp in northern Uganda. These dancers – The White Family – are among a number of South Sudanese refugees hoping to win the Bidibidis Got Talent project and the chance to be mentored by established Ugandan artists.

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On Wednesday, a spectator captures the opening ceremony for the biggest solar plant in West Africa. Burkina Faso’s national power company says the 55-hectare site near the capital, Ouagadougou, will provide electricity for tens of thousands of people.

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A member of Johane Masowe Vadzidzi VaJesu, a Christian group in Zimbabwe, waits for President Emmerson Mnangagwa’s inauguration to begin at the National Sport Stadium in Harare on Friday.

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Beforehand, a soldier pulls a funny face during drills in preparation for President Mnangagwa’s swearing in. The one-time protégé of former President Robert Mugabe had been sacked from his post as vice-president several weeks earlier, but after a military takeover and President Mugabe’s subsequent resignation, Mr Mnangagwa was named leader of the governing Zanu-PF party and Zimbabwe’s premier.

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On Friday, Moroccan children head to the Great Mosque of Sale near the capital, Rabat, to pray for rain. The king has issued a royal decree for citizens to pray for rainfall and end the dry spell troubling Morocco’s agricultural sector.

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AFP

A shipwrecked migrant battles waves in the Mediterranean sea to board an NGO search and rescue boat on Wednesday.

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Days earlier, African migrants are pictured in a courtyard at a detention centre on the outskirts of the Libyan capital, Tripoli. Recent footage of slave markets – where African migrants hoping to reach Europe are instead sold to Libyans for unpaid labour – has caused outrage.

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A visitor to Cairo’s Egyptian Museum inspects the sarcophagus of Pharaoh Tutankhamun on Tuesday.

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While a farmer holds his balance as he picks mandarins in Boufarik, Algeria’s so-called City of Oranges.

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On Friday, Somali children play in the surf at Jazera beach, a popular spot on the outskirts of the capital, Mogadishu.

Images courtesy of AFP, EPA, Getty Images and Reuters

Article source: http://www.bbc.co.uk/news/world-africa-42180403

Week in pictures: 25 November

Our selection of some of the most striking news photographs taken around the world this week.

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Xinhua/REX/Shutterstock

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Thousands of people on the Indonesian island of Bali were forced to leave their homes amid fears of a major eruption from Mount Agung. The volcano’s last big eruption was more than 50 years ago – and left more than 1,000 people dead.

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ORLANDO SIERRA/AFP

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Supporters of the main opposition candidate in the Honduran presidential election set a barricade alight during a protest outside the Electoral Supreme Court. Salvador Nasralla has said he will not accept the poll count despite earlier vowing to respect it.

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Ajay Verma/REUTERS

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A student in Chandigarh, India, displays his face and hand, painted with messages during an HIV/AIDS awareness campaign to mark World Aids Day.

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HANNAH MCKAY/Reuters

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Farmer Andrew d’Angibau carries a freshly harvested tree through a Christmas tree field at Wick Farm in Colchester, Britain.

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Susana Vera/Reuters

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Rohingya Muslims get squeezed as they wait to receive aid at Kutupalong refugee camp, in Cox’s Bazar, Bangladesh. Tens of thousands of Rohingya have been fleeing from violence in Myanmar since late August.

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DANIEL LEAL-OLIVAS/afp

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Britain’s Prince Harry announced he is to marry US actress girlfriend Meghan Markle. The couple, who have been dating since the summer of 2016, smiled as they posed for photographs outside Kensington Palace in London.

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Jane Barlow/PA

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Edinburgh Castle was illuminated to mark St Andrew’s Day in Scotland.

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LINO MIRGELER/afp

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A steam train of the Harzer Schmalspurbahn narrow-gauge railway arrives at Brocken station, which was blanketed in snow, in Wernigerode, Germany.

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Mukesh Gupta/REUTERS

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A man washes a blanket on the banks of the Tawi River in Jammu.

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Baz Ratner/REUTERS

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People fall to the ground as police fire tear gas to control a crowd trying to force their way into a stadium to attend the inauguration of President Uhuru Kenyatta at Kasarani Stadium in Nairobi, Kenya.

All photographs are copyrighted.

Article source: http://www.bbc.co.uk/news/in-pictures-42194551