Pumice rafting

Pumice stone. You know that small grey rock that you probably have lying around in your shower and use occasionally to scrub the dead layer of skin from the soles of your feet?

Pumice Clast

Have you ever wondered where it comes from? And what role it plays in the environment?

Well, this web-page contains information on the ‘secret life of pumice‘!

Specifically, how some pumice stones, provide a mass transportation system for trillions of marine hitchhikers. These hitchhikers make an epic voyage from the middle of the Pacific Ocean to the east coast of Australia and beyond.

Alternatively if you are strapped for time and prefer to watch a short 3 minute video of me presenting my research at the FameLab National Finals in Perth 2015 – click here.

The Havre Volcano
Pumice stone is actually formed from the highly explosive eruption of underwater volcanoes or volcanoes close to shorelines. For example, The Havre Volcano (see image below) is an underwater volcano which lies on the Kermadec arc (see map below image) just North-east of New Zealand which erupted in July 2012 and formed the pumice raft that I studied.

The Havre Volcano

The Havre Volcano just after the 2012 eruption. Source: http://www.niwa.co.nz/news/first-sighting-of-volcano-responsible-for-undersea-eruption. Credit: Joshu Mountjoy


The Kermadec Arc – showing the location of the Havre Seamount. Source: volcano.si.edu

But how can pumice float?

Once the pumice stone is formed it is able to float, and this is because pumice stone is filled with millions of tiny gas-filled chambers – much like a Cadbury aero bar (if you are from Australia you will know what this is – but see images below). And when many pieces of pumice are formed from a volcanic eruption and they all float together on the surface of the ocean or water body they form what is known as a ‘pumice raft’.


Cross-section of a Cadbury aero bar and pumice clast

Now when the pumice is formed, generally it’s not just a couple of pieces it’s more, a lot more. It’s actually trillions of pieces. For example the volcano that formed the pumice raft I am studying – the Havre volcano – formed approximately 4 trillion pieces when it erupted in July 2012. Which as you can imagine formed an absolutely enormous pumice raft that was initially the area of Belgium and eventually spread out to equal the area of France. That’s equivalent to approximately 500 million Olympic sized swimming pools and it was so large it could even be seen from space – see the NASA image of the pumice raft below:


The Havre pumice raft as see from space – Wow! Source: http://earthobservatory.nasa.gov

So these pumice stones can be thought of as mini-islands (see the link to the Theory of Island Biogeography?) and they float around the Pacific Ocean and over-time they are colonised by all kinds of marine biota.


This is a piece of Havre pumice my husband and I photographed at Main Beach, North Stradbroke Island, January 2015. Notice the anemones and barnacles attached and thriving on the pumice mini-island.

Okay so what happens next?

These biota essentially hitchhike across the ocean to the coastlines of islands and continents and as such provide a mass dispersion avenue for all of these sedentary organisms (anemones, corals, barnacles, algae etc) which without pumice or other floating substrates (e.g., algae, wood) would be stuck in their home range and would never colonise new ecosystems.

As a result, this study may help us to understand the way shallow marine biodiversity assembles and may also allow us to understand how and why the Great Barrier Reef was formed.


The amazingly beautiful Great Barrier Reef. Source: “Amazing Great Barrier Reef 1” by Sarah_Ackerman – http://www.flickr.com/photos/sackerman519/4251357083/. Licensed under CC BY 2.0 via Wikimedia Commons


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