The ocean-floor is famously unexplored and is imaged in much less detail than the surfaces of Mars, Moon and Venus.
Draining the water from the oceans would reveal a huge and mostly unknown volcanic landscape. In fact, the majority’ of Earth’s volcanic activity occurs underwater and at depths of several kilometers in deep ocean.
But in contrast to terrestrial volcanoes, even detecting that eruption has occurred on the seafloor is extremely challenging.
Consequently, there remains much for scientists to find out about submarine volcanism and its role in marine environment.
Now our new study on deep-sea eruptions, published in Nature Communications, gives important insights.
Scientists didn’t realize truth extent of oceanic volcanism until the 1950s, once they discovered the worldwide mid-ocean ridge system. This finding was pivotal to the theory of plate tectonics . The network of volcanic ridges runs quite 60,000 kilometers round the globe.
Subsequent exploration led to the detection of “black smoker“ vents, where mineral-rich “hydrothermal“ fluids (heated water in Earth’s crust) are ejected into the deep ocean.
Driven by heat from the underlying magma, these systems influence the chemistry of the whole oceans. The vents also host “extremophiles“ – organisms that survive in extreme environments that were once thought to be unable to sustain life.
But many questions remain. it’s long been thought that deep sea eruptions themselves are rather uninteresting compared to the different types of eruptive styles observed-on-land.
Terrestrial volcanoes that produce similar sorts of magma to those on the seafloor, like in Hawaii or Iceland, often produce spectacular explosive eruptions, dispersing volcanic ash (called tephra). this sort of eruption was thought to be highly improbable in deep-ocean thanks to the pressure from the overlying water.
But data collected via remotely operated submarine vehicles has shown that tephra deposits are surprisingly common on the seafloor. Some marine micro-organisms (foraminifera) even use this volcanic ash to construct their shells.
These eruptions are probably driven by expanding bubbles of CO2 . Steam, which is essentially liable for explosive eruptions-on-land, cannot form at high-pressures.
Scientists have also sporadically detected massive regions of hydrothermal fluid in ocean above volcanic ridges. These enigmatic regions of heated, chemical-rich water are referred to as megaplumes.
Their size is actually immense, with volumes which will exceed 100 cubic kilometers – like over 40 million Olympic swimming pools.
But while they appear to be linked to seafloor eruptions, their origin has remained a mystery.
Megaplumes mystery
In our study, we used a mathematical model to define the dispersal of submarine tephra through the ocean. because of detailed mapping of a volcanic ash deposit in north-east Pacific, we all know that this tephra can spread up to many kilometers from the location of an eruption.
This can’t be explained easily by tides or other oceanic currents. Our results instead suggest that the plumes must be highly energetic. just like the atmospheric plumes seen at terrestrial volcanoes, these initially rise upwards through the water before spreading out horizontally.
The heat transfer required to drive this flow, and carry the tephra with it, is surprisingly large at around one terawatt (double that required to power the whole USA at once). We calculated that this could create plumes of an identical or similar size that has indeed been measured.
Our work provides strong evidence that megaplumes are linked to active seafloor eruptions which they form very rapidly, probably in matter of hours.
So, what’s the precise source of this intense input of warmth and chemicals that ultimately creates a megaplume? the foremost obvious candidate is in fact the freshly erupted molten lava. initially glance, our results appeared to support such a hypothesis.
They show that megaplume formation occurs concurrently with the eruption of lava and tephra. But once we calculated the quantity of lava required for this it had been unrealistically high, around 10 times greater than most submarine lava flows.
Our best guess for now’s that, while megaplume creation is closely linked to seafloor eruptions, they primarily owe their origin to the emptying of reservoirs of hydrothermal fluids that are already present within the ocean crust. As magma forces its way upwards to feed seafloor eruptions, it’s going to drive this hot (>300°C) fluid with it.
Extreme life
We now know that diverse microorganisms live-in-rocks below the surface. As startling because the discovery of extremophile lifeforms around hydrothermal vents was, this discovery pushed our ideas of what life is, and where it’d exist, even further.
The fact that our research suggests that megaplumes come from the crust is according to the detection of such bacteria within some megaplumes.
The rapid outpouring of fluids related to megaplume formation may very well be the first mechanism that disperses these microorganisms from their subterranean origin. If so, then deep-sea volcanic activity is a crucial factor influencing the geography of those extremophile communities.
Some scientists believe that the weird physical and chemical conditions related to seafloor hydrothermal systems may have provided an appropriate environment for the origin of life on Earth. Megaplumes may therefore are involved in spreading this life across the ocean.
If life is to be found elsewhere in our solar-system then hydrothermal vents, like those thought to exist on Saturn’s moon Enceladus, would be an better place to seem .
In the absence of other sources of nutrients & light, these sorts of organisms – possibly the primary to exist on our planet – owe their existence to the warmth and chemicals supplied by the magma that rises upwards to feed seafloor volcanoes.
Since megaplume-transported volcanic ash deposits seem to be common at deep sea volcanoes, the results of our research suggest that the proliferation of life through megaplume emissions could also be widespread.
While having the ability to watch a deep-sea eruption face to face remains unlikely for now, efforts are being made to gather data on submarine volcanic events.
The most notable of those is that the observatory at Axial Volcano in Pacific. This array of seafloor instruments can stream data in real time, capturing events as they happen.
Through efforts like these, together with continued mapping and sampling of the ocean bottom, the volcanic character of the oceans is slowly being revealed.
David Ferguson, Research Fellow in volcanic processes, University of Leeds and Sam Pegler, University Academic Fellow in applied math , University of Leeds.
The findings are reported on Nature communication.
