Elementary school children play outside their classrooms as mount Sinabung volcano spews thick volcanic ash in the background on February 10, 2017 in Karo, Indonesia. Mount Sinabung is one of the most active volcanoes in Indonesia and last erupted in May 2016, killing seven people. (Photo by Albert Damanik/Barcroft Images)

A photo taken on August 29, 2014, shows Mount Tavurvur erupting in eastern Papua New Guinea, spewing rocks and ash into the air, forcing the evacuation of local communities and international flights to be re-routed. Mount Tavurvur, which destroyed the town of Rabaul when it erupted simultaneously with nearby Mount Vulcan in 1994, rumbled to life early in the morning on the tip of the remote island of New Britain. (Photo by Oliver Bluett/AFP Photo)

Dhruva Aliman does a back somersault as he dismounts from a slackline on the beach at Santa Monica, California on October 19, 2014. Slackline is a balance sport where a line of webbing is adjusted at different levels of tension between two anchor points and participants (called slackers) perform tricks and stunts including somersaults. (Photo by Mark Ralston/AFP Photo)

Russia's Maria Stavitskaia performs during the ladies short program at the Rostelecom Cup ISU Grand Prix of Figure Skating in Moscow November 14, 2014. (Photo by Grigory Dukor/Reuters)

Shoppers wrestle over a television as they compete to purchase retail items on “Black Friday” at an Asda superstore in Wembley, north London November 28, 2014. Britain's high streets, malls and online sites were awash with discounts on Friday as more retailers than ever embraced U.S.-style “Black Friday” promotions, seeking to kickstart trading in the key Christmas period. In the United States the Friday following the Thanksgiving Day holiday is called Black Friday because spending usually surges and indicates the point at which American retailers begin to turn a profit for the year, or go “into the black”. (Photo by Luke MacGregor/Reuters)

(L-R) Poppy Delevingne, Model of the Year Cara Delevingne, Joan Smalls and Karlie Kloss pose in the winners room at the British Fashion Awards at London Coliseum on December 1, 2014 in London, England. (Photo by Pascal Le Segretain/Getty Images)

People are seen on a street in Havana December 17, 2014. Stunned Cubans celebrated an apparent end to decades of conflict with the United States on Wednesday after both governments said they would restore diplomatic relations cut off in 1961. Many said they expected a restoration of ties would lead to the end of a U.S. economic embargo against Cuba, which is vilified daily in the official media and which Cubans accept as a key cause of widespread poverty on the island. (Photo by Reuters/Stringer)

Dog Xiaoniu dressed in clothes walks across a street with its owner (not pictured) in Shanghai, December 19, 2014. According to local media, Xiaoniu accompanies its owner to the food market everyday and is able to walk with its hind legs for up to about an hour. (Photo by Reuters/Stringer)