Floating Rocks

At times, the Sea holds much more secrets than we could possibly imagine. From the abyssal environments of which we know nothing to the shallows that are beyond our understanding, there is yet another curious surface that the marine organisms so gladly colonize – the pumice raft.

The pumice raft is a floating mobile accumulation of low-density pumice clasts that generate as a result of silicic volcanic eruption. So imagine a submarine volcano that at some point starts to erupt, and the hot silicic magma undergoes vesiculation and quenching to become pumice. Once this clastic sediment is formed, instead of sinking to the sea floor, it floats up to the surface. Indeed, the vesiculation of the magma creates numerous tiny chambers.

Hence the pumice rafts work perfectly as a colonization substrata for many marine organisms, such as cyanobacteria, macroalgae, barnacles, molluscs, bryozoans and polychaetes. Not only; it has been studied that when mobile organisms associated with the pumice rock and the sessile organisms leave or decompose, respectively, the substrate becomes a magnet for polyps (phylum Cnidaria). These polyps begin to grow because of the perfect habitat – the pumice moves and so the water around changes, continuously bringing food to the polypoid body.

Scott E. Bryan et al., 2012

Having been completely waterlogged or colonized by different marine species, the pumice clast becomes denser than the water and sinks to the bottom of the sea. Scientists have been researching these sediments for a long time and they have discovered that when the pumice sinks, it enriches the bottom. Seems pretty logical since the sediment is no longer only of inorganic matter (minerals) but of organic, too.

Sometimes though, the pumice raft remains lighter than the water despite the colonization by organisms. And so it continues to float until the strong currents and waves push it towards the beaches where it strands, or towards atolls where it is dragged by the high tide towards the lagoon.

Not only the volcanic-derived rock enriches the marine ecosystems, but it is also a great dispersal tool for organisms that, if the conditions suit their life requests, widen their habitat range.

Scott E. Bryan et al., 2012

Recently, a couple that was sailing with a catamaran towards Fiji, got stuck in a pumice rock accumulation as big as 150 sq meters! The floating rocky mass erupted from the submarine volcano of Tonga, Australia, and has been spotted by NASA’s satellites. Scientists have been watching the movement of the rocky carpet, which is believed to be moving towards the Great Barrier Reef. Some of the scientists even think that this pumice raft could replenish the lost corals of one of the most productive ecosystems of the world.

With that said, I am starting to think that Mother Earth is finding its way to mitigate the catastrophes, which to some extent are humans’ fault. It is as if the Universe’s tendency is to reestablish balance and work towards the syntropy – the exact opposite of what I have been taught at the first ecology lecture, where the main title of the presentation was Entropy.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s