Merit Prize Winner: “A Well Earned Rest in the Sahara”. This photo of Moussa Macher, our Tuareg guide, was taken at the summit of Tin-Merzouga, the largest dune (or erg) in the Tadrat region of the Sahara desert in southern Algeria. Moussa rested while waiting for us to finish our 45-minute struggle to the top. It only took ten minutes of rolling, running, and jumping to get back down. The Tadrat is part of the Tassili N'Ajjer National Park World Heritage area, famous for its red sand and engravings and rock paintings of cattle, elephants, giraffes, and rhinos that lived there when the climate was milder. Photo location: Summit of Tin-Merzouga, Tadrat, Tassili N'Ajjer National Park, Algeria. (Photo and caption by Evan Cole/National Geographic Photo Contest)

Turkana tribesmen walk with guns to protect their cattle from rival tribes near Baragoy, Kenya August 4, 2017. (Photo by Goran Tomasevic/Reuters)

Thousands gather to rally for marriage equality ahead of a national postal survey on September 10, 2017 in Sydney, Australia. The High Court handed down its decision on Thursday to allow the government's proposed postal ballot survey to go ahead. Ballots with the question “Should the law be changed to allow same-sеx couples to marry?” will be sent to households across Australia on September 12. (Photo by Jonny Weeks/The Guardian)

Balinese man watches Mount Agung volcano almost covered with clouds as he stands at a temple in Karangasem, Bali, Indonesia, Tuesday, September 26, 2017. An increasing frequency of tremors from the volcano indicates magma is continuing to move toward the surface and an eruption is possible, a disaster agency official said Tuesday. Tourists are cutting short their stay to the island, where an eruption would force the airport to close and strand thousands. (Photo by Firdia Lisnawati/AP Photo)

Actress Liv Tyler, 40, stripped in shots for the Triumph Essence's Autumn/Winter 2017 campaign in November, 2017. The Essence line is Triumph’s premium offering, with this season taking on the theme of “opulent Art Nouveau”, featuring designs in velvet embellished mesh, Leavers lace and silk satin. (Photo by Rankin/The Mega Agency)

Homeless man Alonzo Harrison, 47, takes a nap on a bench at Pershing Square decorated with Christmas lights in the background on Monday, December 4, 2017, in Los Angeles. A homeless crisis of unprecedented proportions is rocking the West Coast, and its victims are being left behind by the very things that mark the region's success: soaring housing costs, rock-bottom vacancy rates and a roaring economy that waits for no one. (Photo by Jae C. Hong/AP Photo)

In this January 3, 2018 photo several female Gelada baboons, also known as bleeding-heart baboons, cuddle with their youngs in order to keep warm at the Wilhelma zoo in Stuttgart, Germany. (Photo by Sebastian Gollnow/DPA via AP Photo)

Arlo Dela Cruz and Maica Nicerio-Dela Cruz on their wedding day with the Mayon volcano erupting in the background, in Daraga, Albay, Philippines on January 25, 2018. They were married earlier in the afternoon at Our Lady of the Gate Parish. After their wedding they walked out to Red Labuyo restaurant and the volcano started its eruption. The Mayon volcano continued to erupt Thursday. The airport in Legazpi is closed until at least 31 January 2018. (Photo by ZUMA Press/Alamy Stock Photo)