Asphalt volcano

[3] One hypothesis is that the tar is relatively hot when it comes out of the seafloor, but just like undersea lava flows, it is quickly cooled by the much colder seawater around it.

[2] This produces forms similar to the distinctive A'a and pahoehoe types of basalt lava flow seen in places like Hawaii.

[2][4] The article suggested that water heated past the critical point underneath the seafloor found a passageway to the surface, most likely a salt dome, and carried with it a heavy load of hydrocarbons and dissolved minerals.

[2] The lighter compounds in the mixture escape to the surface, while the tar and other heavier materials remain on the seafloor, eventually building up the asphalt volcano's structure.

Instead, the pāhoehoe-like textures might result from gradients in viscosity, driven by the loss of volatile components, which create a contrast between the flow's outer crust and its inner core.

The unusual features were first noted by Ed Keller on bathymetric surveys conducted in the 1990s, and first viewed by a team led by David Valentine in 2007, utilizing DSV Alvin.

The two largest structures, less than 1 km (1 mi) apart, are pocked by pits and depressions, a sign of methane gas bubbling up long ago.

In addition, as much as 20% of its mass is made of "junk"—microscopic organisms, sand, and miscellaneous materials that gradually accumulated in the oil.

[1] Analysis of the samples collected from the mounds suggest that they required several decades, even centuries, to build up their current bulk, and that the volcanoes last erupted around 35,000 years ago.