Ngorongoro Crater (Tanzania). At 610m deep and 260 sq km, this is the largest unflooded caldera in the world. A blue-green vision from above it's a haven for engangered wildlife and Maasai livestock. The crater was formed three million years ago when a giant volcano, which could have been as high as Kilimanjaro, exploded and collapsed. The caldera formed the concentric fractures in the crust cracked down to a magma reservoir deep underground. (Photo by John Bryant/Getty Images)

A woman poses by “Leaf Spirit” by Simon Gudgeon at the FORM 24 show at Sculpture by the Lakes, on April 02, 2024 in Dorchester, England. The award-winning sculpture show runs from April 2 to June 1, with works by more than 35 leading contemporary sculptors exhibited throughout 26-acres of lakes, rivers, gardens, and woodlands as well as in the Gallery and The Retreat. FORM includes a series of talks and events to accompany the exhibition, including “Meet the Artist” Q&A sessions with exhibiting sculptors, workshops and demonstrations. (Photo by Finnbarr Webster/Getty Images)

These beautiful shots may look like works of modern art – but they are actually close-ups of chemical reactions. The works were snapped with the help of a group of scientists from the University of Science and Technology of China (USTC) in Anhui, China. Here: Zinc reacting with lead nitrate in a soft gel to form lead crystals. (Photo by Yan Liang/Caters News)

A remote-controlled plane in the form of a witch flies over a neighborhood as the sun sets during Halloween in Encinitas, California, U.S. October 31, 2016. (Photo by Mike Blake/Reuters)

Layers of breathtaking colour streak the rolling hills of this vast desert, making the landscape appear as though it has been tie-dyed. The natural phenomenon, nicknamed the “Painted Desert”, was formed when the area was once a river floodplain. Each colour corresponds to a different underground geological feature – rocks which have seemingly dyed the layers of earth above. Formed from volcanic activity, the hills at the John Day Fossil Beds National Monument in East Central Oregon, USA, are almost bursting with colour. Pictured: The colourful hills at the John Day Fossil Beds National Monument in East Central Oregon, USA. (Photo by Mark Brodkin/Solent News/SIPA Press)

South Korea's Black Eagles aerobatics team performs an aerial display forming a Ying and Yang logo during the Singapore Airshow at Changi exhibition center in Singapore on February 16, 2016. (Photo by Roslan Rahman/AFP Photo)

A truck laden with logs travels in Araribóia Indigenous Reserve, Maranhão, Brazil on August 7, 2015. Loggers have been stealing hardwood trees from indigenous lands in Brazil. The Guardians of the Forest are an armed militia formed by the Guajajara tribe to protect their reserve. (Photo by Bonnie Jo Mount/The Washington Post)

“Thunderstruck”. Summer stom. A super cell formed off the coast of New Zealand, intensified and swept across Christchurch and North Canterbury, February 23, 2014. Photo location: Christchurch, New Zealand. (Photo and caption by David Hardy/National Geographic Photo Contest)