A geological chimney
Off the coast of Western Australia, the seafloor is not as quiet as it seems. Here, a geological feature known as the Giralia Anticline is a natural conduit for methane gas. An anticline is an arch-like fold of stratified rock, and the Giralia structure is a massive one, extending about 80 miles. This formation has trapped ancient hydrocarbon deposits deep beneath the seabed. The gas originates from source rocks of the Devonian and Early Carboniferous periods, making the methane itself hundreds of millions of years old.
Over geologic time, faults and fractures within the anticline have allowed this fossil gas to migrate upwards, seeping directly into the cold waters of the deep sea. This feature is a cold seep, where hydrocarbons and sulfides emerge from the ocean floor at temperatures close to that of the surrounding seawater. These seeps provide a rare energy source in the deep ocean, an environment without sunlight for photosynthesis. The Giralia Anticline is part of the larger Carnarvon Basin, a vast geological province covering approximately 115,000 square kilometers onshore and another 535,000 square kilometers offshore.