This combination of April 15, 2013 and April 2, 2014 photos show a police officer clearing Boylston Street following a bomb blast near the finish line of the 2013 Boston Marathon, and pedestrians crossing at the same corner nearly a year later in Boston. (Photo by Charles Krupa/AP Photo)

Storm chaser Brad Mack from Buena Park California videotapes a rotating supercell storm west of Newcastle, Texas April 9, 2013. Many of the storms in Tornado Alley that were forecast to be severe this week were taken out by a cold front from Canada. Picture taken April 9, 2013. (Photo by Gene Blevins/Reuters)

View at one of the sculptures by Swiss artist H.R. Giger during the opening of the Ars Electronica 2013 exhibition “HR Giger. The Art of Biomechanics” in Linz, Austria, 04 September 2013. (Photo by EPA/RUBRA)

“In beard and hat”; Udine, Friuli-Venezia Giulia, Italy, 2013. (Photo by Giulio Magnifico)

Huge pack of starlings in the sky of the Negev, Israel, on January 21, 2013. Birds are turned in evening twilight before settling to sleep. (Photo by Eliyahu Hershkovitz)

A burning tank is in Daraa, on March 9, 2013. (Photo by Ali Abu-Salah/Reuters/Shaam News Network via The Atlantic)

A life-size interactive inflatable sculpture of Stonehenge called “Sacrilege 2012” by English contemporary artist Jeremy Deller on display as part of the “Inflation!” exhibition curated by Mobile M + on April 24, 2013 in Hong Kong. The inflatable artwork is one of six on display as part of the exhibition which is open from April 25, 2013 until June 9, 2013. (Photo by Jessica Hromas)

Visitors view ice sculptures at the 29th Harbin International Ice and Snow Festival on January 5, 2013. (Photo by Associated Press)