Popping Rocks: Deep questions on the Mid-Atlantic Ridge
In 1985, a geologic expedition aboard the Soviet research vessel R/V Academician Boris Petrov made a surprising find near the Mid-Atlantic Ridge at 14°N: volcanic rocks that popped when they were brought on deck as a result of volatiles in the rocks escaping under the pressure difference between the seafloor and sea surface. A French graduate student named Phillippe Sarda took some of the rocks back to Paris and found not only that the “popping rocks” contained a high percentage of carbon dioxide gas—in fact, they were among the most carbon-dioxide-rich samples ever studied—but that they also contained nearly pristine samples of noble gases (pdf) from deep beneath the surface of the Earth.
Photographs of thin sections of popping rocks retrieved from 14°N (Sarda & Graham, 1990). Click to enlarge.
Those rocks, basaltic lava that cooled under pressure and from over 1200°C to near freezing within seconds of erupting onto the seafloor, have a glassy outer layer trapping gases that would otherwise escape into the water or the atmosphere. Those gases provide an unparalleled view into the composition and conditions of the deep Earth that could help answer some of the biggest questions about our planet’s history and formation, including the origin of the atmosphere and the oceans and the functioning of the global carbon cycle.
Unfortunately, the precise location where the scientists on board the Academician Boris Petrov made their discovery is lost to pre-GPS history. We do know that they come from a complex region of the Mid-Atlantic Ridge that contains vast areas of lava flows as well as heavily faulted terrain with intact blocks of deep crust. The popping rocks come from the boundary between these two very different types geology.
The goal of our NSF-funded mission is to take the towed instrument platform Towcam, autonomous underwater vehicle Sentry and the human-occupied submersible Alvin on board the modern research vessel Atlantis back to 14°N to find lava flows that contain popping rocks and , carefully map the volcanic and structural features of the rift valley where they are located and better understand the geological history of this portion of the global mid-ocean ridge. We will use Towcam to scout for promising geologic settings, then launch he programmable, unmanned Sentry to make high-resolution maps of the seafloor to help us pinpoint locations for Alvin to dive and retrieve new samples of popping rocks.
If we are successful, we will return home with new samples that provide clues to help answer some very deep questions about the nature of our planet.
