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)

A dog waits to be blessed by a priest outside San Anton Church in Mijas, near Malaga, Spain, January 17, 2017. Hundreds of pet owners bring their animals to be blessed every year on the day of Saint Anthony, Spain's patron saint of animals. (Photo by Jon Nazca/Reuters)

A woman watches the St. Patrick's day parade in Dublin, Ireland on March 17, 2017. St. Patrick's Day is marked annually on 17 March to commemorate Saint Patrick, a patron saint of Ireland. (Photo by Clodagh Kilcoyne/Reuters)

A participant in the traditional dance of Los Historiantes poses for a photo during festivities in honour of St. Michael the Archangel in San Miguel Tepezontes, El Salvador September 28, 2016. (Photo by Jose Cabezas/Reuters)

Spectators dressed as leprechauns attend St Patrick's Day parade in Dublin on March 17, 2014. (Photo by Peter Muhly/AFP Photo)