An Estonian competitor cheers during the “World Medieval Fighting Championship – the Israeli Challenge” in Rishon Letzion near Tel Aviv January 22, 2015. Israel hosted the tournament on Thursday, which includes 14 competitors from seven different countries – France, Belarus, Denmark, Estonia, Russia, Ukraine and Israel. (Photo by Amir Cohen/Reuters)

A robot is seen on Mount Etna, Italy on July 4, 2017. Mount Etna, in Sicily, is a test bed for the approximately three-foot high, four-wheeled machine ahead of a future mission to the moon. It is being conducted by the German Aerospace Centre, the agency which runs Germany's space programme. (Photo by Antonio Parrinello/Reuters)

In this Tuesday, March 10, 2015 photo, rime ice covers rocks on the summit of Mount Washington in New Hampshire. Rime ice occurs when freezing fog hits stationary objects in frigid conditions. (Photo by Robert F. Bukaty/AP Photo)

On the western side of Mount Hood lies the longest glacier cave system in the contiguous United States. In 2012, these caves were mapped to a combined length of 7,166.8 feet by cave explorers Brent McGregor and Eddy Cartaya. Currently, the total passage length is hundreds of feet less. Glaciers are frozen rivers; they are always moving and changing... (Photo and caption by Josh Hydeman)

Starting in September, Indonesia's Mount Sinabung began erupting yet again. In the days that followed, ash and smoke were shot into the air multiple times. As a result, nearby towns turned gray from repeated blows by the volcano. Photo: A man uses his mobile phone as Mount Sinabung continues to erupt, with hot smoke spewing from the volcano, in the Karo district on the north of Indonesia's Sumatra island on November 18, 2013. Officials said a week ago at more than 5,000 people had fled their homes since the volcano erupted early this month. (Photo by Sutanta Aditya/AFP Photo)

Competitors take part in the International Medieval Combat Federation World Championships at Scone Palace on May 10, 2018 in Perth, Scotland. Thousands of visitors are expected to attend the crowning place of Scottish Kings, Scone Palace for the IMCF World Championships which has five hundred competitors and officials from all over the world, from the UK to as far afield as Australia, South Africa and Mexico. (Photo by Jeff J. Mitchell/Getty Images)

An Indian woman collects camel dung during the annual cattle fair in Pushkar, in the western Indian state of Rajasthan, Sunday, November 10, 2013. Pushkar, located on the banks of Pushkar Lake, is a popular Hindu pilgrimage spot that is also frequented by foreign tourists who come to the town for the annual cattle fair and camel races. (Photo by Ajit Solanki/AP Photo)

Travellers ride their horse through the river during the Appleby Horse Fair on June 5, 2014 in Appleby, England. The Appleby Horse Fair has existed under the protection of a charter granted by James II since 1685 and is one of the key gathering points for the Romany, gypsy and traveling community. The fair is attended by about 5,000 travellers who come to buy and sell horses. The animals are washed and groomed before being ridden at high speed along the “mad mile” for the viewing of potential buyers. (Photo by Nigel Roddis/Getty Images)