The ocean floor is famously unexplored and is painted in much less detail than the surfaces of Mars, the Moon and Venus.
A discharge of water from the ocean would reveal a vast and mostly unknown volcanic landscape. In fact, most of the Earth’s volcanic activity occurs underwater and at depths of several kilometers in the deep ocean.
But unlike terrestrial volcanoes, even detecting an eruption on the seabed is extremely challenging.
Consequently, scientists have much to learn about submarine volcanism and its role in the marine environment.
Now our new study on deep sea eruptions is published in Nature Communications, provides important insights.
Scientists did not understand the true extent of oceanic volcanism until the 1950s, when they discovered the global system of the mid-ocean ridge. This discovery was crucial to plate tectonics theory. The network of volcanic reefs travels more than 60,000 kilometers worldwide.
Subsequent research led to the discovery of the “black smoker’s” opening, where “hydrothermal” liquids rich in minerals (heated water in the Earth’s crust) are released into the deep ocean.
Driven by heat from the basic magma, these systems affect the chemistry of the entire oceans. Ventilation openings also host “extremophiles” – organisms that survive in an extreme environment that was once thought to be unable to sustain life.
But many questions remain. For a long time, deep sea eruptions themselves were considered quite uninteresting in relation to the variety of eruptive styles observed on land.
Terrestrial volcanoes that produce similar types of magma as those on the seabed, such as Hawaii or Iceland, often produce spectacular explosive eruptions, scattering volcanic ash (called tephra). This type of eruption was thought to be very unbelievable in the deep ocean due to the pressure of the water being covered.
But data collected by remote-controlled submarines have shown that tephra deposits are surprisingly common on the seabed. Some marine microorganisms (foraminifera) even use this volcanic ash to make their shells.
These eruptions were probably triggered by the expansion of carbon dioxide bubbles. The steam, which is largely responsible for explosive eruptions on land, cannot be formed under high pressure.
Scientists have also sporadically discovered massive areas of hydrothermal fluid in the ocean above volcanic reefs. These enigmatic areas of heated water rich in chemicals are known as megaplums.
Their size is really huge, with quantities that can exceed 100 cubic kilometers – which is equivalent to more than 40 million Olympic pools.
But while they appear to be linked to seabed eruptions, their origins remain a mystery.
In our study, we used a mathematical model to explain the spread of submarine tephra by the ocean. Thanks to detailed mapping of volcanic ash deposits in the Northeast Pacific, we know that this tephra can extend up to several kilometers from the site of the eruption.
This cannot be easily explained by tides or other ocean currents. Our results instead suggest that feathers must be very energetic. Like atmospheric feathers seen on terrestrial volcanoes, they initially rise upward through water before spreading horizontally.
The heat transfer required to drive this flow and carry the tephra with it is surprisingly large, about one terawatt (twice as much as needed to power the entire U.S. at once). We calculated that this should create feathers of a similar size that was actually measured.
Our work provides strong evidence that megaplums are associated with active seabed eruptions and that they form very rapidly, probably within a few hours.
So what is the specific source of this intense heat and chemical intake that ultimately creates a megaplum? The most obvious candidate is, of course, freshly erupted molten lava. At first glance, our results seemed to support such a hypothesis.
They show that the formation of megaplums occurs simultaneously with the eruption of lava and tephra. But when we calculated the amount of lava needed for that, it was unrealistically high, about ten times higher than most underwater lava flows.
For now, our best assumption is that, although megaplum formation is closely related to seabed eruptions, their origin is primarily due to the emptying of reservoirs of hydrothermal liquids already present in the oceanic crust. As magma is forced upward to feed seabed eruptions, it can move this hot (> 300 ° C) fluid.
We now know that various microorganisms live in the rocks below the surface. As astonishing as the discovery of extremophile life forms around hydrothermal vents was, this discovery pushed our ideas even more about what life is like and where it could exist.
The fact that our research suggests that megaplums originate from the cortex is consistent with the detection of such bacteria in some megaplums.
The rapid outpouring of fluid associated with megaplum formation may actually be the primary mechanism that dissipates these microorganisms of subterranean origin. If so, then deep-sea volcanic activity is an important factor influencing the geography of these extremophile communities.
Some scientists believe that the unusual physical and chemical conditions associated with the seabed’s hydrothermal systems could have provided a conducive environment for life on Earth. Megaplums could therefore be involved in the spread of this life across the ocean.
If life can be found elsewhere in our solar system, then hydrothermal vents, like those thought to exist on Saturn’s moon Enceladus, would be a good place to look.
In the absence of other sources of nutrients and light, these types of organisms – perhaps the first to exist on our planet – owe their existence to the heat and chemicals supplied by rising magma to power volcanoes from the seabed.
Because volcanic ash deposits transported by megaplum appear to be common in deep-sea volcanoes, the results of our study suggest that the spread of life by megaplum emission may be widespread.
Although the possibility of a personal observation of a deep-sea eruption is unlikely for now, efforts are being made to collect data on underwater volcanic events.
The most significant of these is the Axial Volcano Observatory in the Pacific Ocean. This set of instruments on the seabed can stream real-time data, capturing events as they occur.
Through such efforts, along with continuous mapping and sampling of the ocean floor, the volcanic character of the ocean is slowly being revealed.
David Ferguson, researcher for volcanic processes, University of Leeds and Sam Pegler, university academic associate for applied mathematics, University of Leeds.
This article was published in The Conversation magazine under a Creative Commons license. Read the original article.