Methane Bubbling through Seafloor Creates Undersea Hills
09.02.2007 - Other
According to a recent paper published by MBARI geologists and their colleagues, methane gas bubbling through seafloor sediments has created hundreds of low hills on the floor of the Arctic Ocean.
These small, dome-shaped, ice-cored hills, are found in many Arctic regions and have puzzled scientists ever since they were first discovered in the 1940s. Previous studies have suggested that they formed on land but were submerged when sea level rose following the end of the last ice age, over 10,000 years ago.
MBARI geologists and their colleagues propose an alternative hypothesis: these features form when methane hydrate (a frozen mixture of gas and seawater) decomposes beneath the seafloor, releasing gas that squeezes deep sediments up onto the seafloor like toothpaste from a tube.
Methane hydrate can only remain solid at low temperatures and high pressures. Such conditions exist several hundred meters below the seafloor in this part of the Arctic Ocean. When the ice sheets from the last ice age melted and the ocean flooded the continental shelves, it caused the seafloor sediment to become warmer, causing some of the buried methane hydrates to decompose, releasing methane into the surrounding sediments.
This newly released methane migrated sideways under the seafloor, held in place by an impermeable layer of frozen soil that lies between the hydrates and the seafloor. Eventually it is collected and moved toward the surface along faults or in other areas where the sediments are weaker.
