As Sakhalin photographer Mikhail Mikhailov took a helicopter ride in eastern Russian skies, he was surprised to look down and see what appeared to be a gigantic human eye looking right back at him.

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The eye turned out to be the Pugachevskiy mud volcano, located on Sakhalin Island.

"There are quite a lot of mud volcanoes in the world, and this one is well-known. But I haven’t ever seen it looking like an eye!” said Mikhailov. 

The illusion was created during an eruption, creating a muddy brown iris around the center of the volcano, which served as the pupil. 

"It was a very strong eruption, the mud was getting out from one point and got spread around evenly,” said Mikhailov.

(MORE: Volcanoes That Could Erupt At Any Time)

According to the U.S. Geological Survey, mud volcanoes are small volcano-shaped cones of mud. They are created as mud erupts from a vent, either flowing as a liquid or ejecting into the air. 

Usually found in subduction zones, mud volcanoes form from any geo-excreted gases and liquids and tend to release methane, although they also release smaller quantities of nitrogen and carbon dioxide. 

"It created a very beautiful view, looking exactly like an earth eye, especially from a helicopter. It is definitely a rare phenomenon,” said Mikhailov. 

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