Tar volcanoes -- rarely seen by geologists, were found accidentally, during a search for shipwrecks. National Oceanic and Atmospheric Administration (NOAA) researchers discovered the structures in Gulf of Mexico. 

Instead of a ruined ship, the team found strange rock structures over 6,200 feet beneath the surface of the water. The stones are laid out like a large flower on the seabed. Investigators saw a mysterious black substance emanating from the "petals" of the structure. 

The tar volcanoes were first spotted by sonar, and later investigated by a robotic submarine, the Deep Discoverer 2 (D2). When the automated craft reached the ocean bottom, it confirmed that both objects seen on sonar were tar volcanoes. 

Investigators found chemosynthetic tube worms near the structures, leading them to believe the formations were the little-seen asphalt volcanoes. 

Although some tar fields on land can be developed to release useable petroleum, this is not possible with tar volcanoes. 

"The asphalt at this site is produced by the same processes that generate oil and gas, but has been transformed by geology and then altered again when it is exposed to cold seawater... Some reservoirs are so old that the oil they contain has been "cooked" for millions of years. Heating causes the volatile components to evaporate, leaving behind a thick, gooey remnant," NOAA officials stated in a press release about the discovery. 

Tar is processed in factories by being mixed with sand and light oil, then heated to create the asphalt used to pave roads. In these volcanoes, the tar is squeezed out from the ocean floor like toothpaste from a tube. Volatile chemicals dissolve in the water, and the formation shrinks. The hard substance quickly became home for a number of different species, including some who lived of the organic material. 

"People following the dive saw beautiful video of corals, barnacles, anemones, and fish. Bacteria that can utilize the oil as food generated a sulfur-based food chain for chemosynthetic tube worms and mats of other sulfur oxidizing bacteria," NOAA explained. 

The area where the tar volcanoes were found is a hotbed for shipwrecks, and archeologists have discovered numerous artifacts in the region. 

In addition to "normal" volcanoes spewing magma, these structures have also been seen erupting with mud, shale and even salt. Additional asphalt volcanoes are also known to exist in the Gulf of Mexico and the California coast, as well as in the waters off western Africa. 

This pair of tar volcanoes is dormant right now, but the size of the petals suggests there may be more material under the structures, waiting to erupt in the future.