NOAA explorers recently made a surprising discovery off the coast of Galveston.

As they explored the ocean floor with underwater robots, they thought they'd found another shipwreck, but there was something odd about this one.

The object had a strange shape, as if palm fronds were shooting up from the ocean floor, and it was covered in marine life.

After some investigation, they realized it wasn't a shipwreck after all but the solidified eruption from an underwater volcano of asphalt. In other words, it's a giant tar ball.

Related on MNN: 10 of the world's most spectacular artificial reefs