A gigantic "island" of pumice drifts in the Pacific

This is a video like no other that brought the catamaran ROAM, which was sailing in the Pacific Ocean on Friday, August 9th. The crew of this boat witnessed an incredible phenomenon: for nearly six hours, they sailed in the middle of a gigantic tablecloth made up of billions of pumice stones. The images are striking, worthy of a science-fiction work on the Dune. One hardly dares to imagine what a seasoned seaman must feel when the sea disappears, even though the boat is nevertheless hundreds of kilometers from the nearest coast. The water is nevertheless there, hidden under these silica balls: its oscillations give the impression of traversing a living mountain, of which each breath raises the sailboat.

But from where can come this strange rock formation of 150km ² adrift in the biggest ocean of the planet? According to scientists, it could be the consequences of the eruption of an underwater volcano.

The best illustration of the magnitude of the phenomenon comes from above: indeed, this sheet is so extensive that it is visible from space. According to the World, the satellite images would reveal that the explosion of the volcano would have occurred on August 7th. Pumice stones are formed within so-called "explosive" volcanoes. As time goes by, the pressure and temperature will increase to a breaking point. At this time, the volcano erupts: the molten rock material will be expelled very violently and undergo a very sudden cooling and depressurization.

This drop in pressure and temperature is accompanied by a significant outgassing, a bit like when you open a can of soda slightly shaken. The gas bubbles, evacuating, leave small cells before the whole is solidified as is. It is this phenomenon that gives the pumice stones their spongy appearance so special, but above all, it gives them an important feature in the case that interests us: the pumice stone has a very low density less than that of water. The consequence is very simple: according to the principle of Archimedes' thrust, the pumice stone formed at the moment of the eruption floats and can therefore rise to the surface in very large quantities. It then drifts in the form of a raft whose size depends on the intensity of the eruption.

A danger for ships …

The phenomenon is not new or isolated: it is well known navigators familiar regions where the ocean floor is the scene of significant volcanic activity. And for good reason: if most pieces of pumice back are small (a few centimeters), others can reach the size of a football. And necessarily, the navigation in the middle of a pile of rock, as light as it is, is not easy thing. In the absence of sufficient winds, the rudder or thrusters of a boat can be completely blocked.

These "pumice rafts" appear quite regularly in the region, according to the various underwater eruptions. But their size can vary drastically: in 2012, during the eruption of the Kermadec Islands, a raft of very different proportions was formed. At the ascent, it measured nearly 400 km² for more than three meters thick! It then spread over the months that followed, until reaching a hallucinating area of ​​26,000km²! After a while, the ocean currents eventually break up and disappear on different coasts.

… But an invaluable scientific treasure

Today, these "pumice rafts"As our counterparts across the Atlantic call them, they are at the center of a lot of fascinating theories. The reason is rather simple: they are real Organic Noah's arches, capable of carrying micro-organisms over thousands of kilometers according to their drift. Whoever is currently traveling in the Pacific should successively reach the Fiji Islands and then New Caledonia. Once left the Kanak Islands, the cluster should then go aground in Oceania, on the east coast of Australia … right on the Great Barrier Reef, the largest coral reef in the world.
This treasure of nature is already in a sorry state, everyone knows it. But no worries: the arrival of the raft should not damage the reef, on the contrary. The microorganisms it carries are potentially capable of regenerating entire ecosystems. This can allow a virtuous circle to take shape by reviving all the subtle and interconnected dynamics that govern coral reefs. From there to saying that the reefs will be saved by pumice islands in full swing, there is a big step, but they can indeed serve as a makeover for ecosystems that need it.

But this renewal of corals is not the only reason they fascinate biologists. Indeed, these rafts could have had a very fundamental role in the distribution of species as we know it today! Several studies suggest that species have been able to move from one continent to another through ice bridges or drifting icebergs during the ice ages of our Earth. In the same way, some imagine that plants, animals and micro-organisms could use it as a means of colonizing other environments!

This idea was particularly developed by Patrick D. Nunn, professor of geography at prestigious King's College London, in his book Vanished Islands and Hidden Continents of the Pacific (2008).
Better: these rafts could have played a central role in the appearance of life! In any case, this is the hypothesis of several research laboratories. In 2011, the team of geologist and biologist Martin D. Brasier of Oxford University, published a study that explains that these rafts would have made a remarkable substrate for life to appear, and this for four reasons: a high surface / volume ratio, permanent presence at an interface between water and air, exposure to a wide variety of conditions, and finally the ability to adsorb heaps of nutrients and other chemical compounds. A real open-air theory of evolution laboratory!