Tim the Yowie Man: Floating stones of Broulee

If you've noticed a proliferation of pumice piling up on your preferred patch of sand this summer, you aren't alone.

''It's perplexing,'' reports Timothy Walsh, of Garran, who, during daily walks on Broulee Beach this week, was surprised by ''the long stretch of pumice strewn along the tide line''.

Apparently, the underwater volcano spewed out a ''raft of pumice estimated to be more than 20,000 square kilometres in size''. That's a surface area bigger than Belgium.

The rocks are ''many sizes, from a few centimetres in diameter to some the size of tennis balls and even larger'', adds the holidaymaker.

The sudden appearance of the volcanic stones (pumice forms when lava from a volcano cools rapidly) on south-coast beaches this summer has baffled Walsh and thousands of fellow beach-goers from as far afield as Batemans Bay to Eden. ''I don't recall seeing this quantity on previous visits,'' he says. ''I wonder where it comes from. There are not too many volcanoes near here.''

While a straw poll of Broulee beach-goers this week drew mostly responses of blank stares (can you blame them - imagine how you'd react if approached by a columnist clad only in budgie smugglers and a tattered akubra, wielding a pen and notebook?) a couple of locals did offer a theory as to the stone's origins.

''Isn't it debris from a volcano north of New Zealand?'' said a 20-something surfer while heading out on his stand-up paddleboard. (Aren't they all the trend this year?)

Sound far-fetched? Well, to solve the riddle once and for all, this columnist promptly contacted Dr Scott Bryan, pumice expert (yes, really!) at the Queensland University of Technology, who confirmed the paddleboarder's story.

''It's the result of the July 2012 eruption of the Havre Seamount, which is about 1000 kilometres north of Auckland,'' explained the rock doctor. Apparently, the underwater volcano spewed out a ''raft of pumice estimated to be more than 20,000 square kilometres in size''. That's a surface area bigger than Belgium.

Further, Bryan said, since the eruption, the pumice has slowly dissipated and has washed up on beaches in Fiji, Tonga, New Zealand and along Australia's east coast, from Torres Strait and now as far south as parts of Victoria.

''The pumice is essentially the only record we have of the eruption. It can help us to understand more about the nature of the volcano, as well as how these volcanoes erupt explosively under so much water,'' he said.

While the pumice may seem quite harmless, unless you kick your toe on a piece while playing beach cricket (ouch!), it also has the potential to bring new species to our shores. ''Species such as goose and acorn barnacles, molluscs, anemones, bristle worms, hydroids, coral and crabs are just some of the creatures which have hitched a ride on the pumice,'' Bryan said. '' Sometimes the weight of the hitch-hikers causes the pumice to sink.''

Not all species are welcome, so Bryan and his scientific colleagues are keeping watch for any invasive marine species arriving on our shores via the pumice.

Not surprisingly, the influx of such a significant amount of pumice is affecting local ecosystems and it appears to already be troubling the seabird population. During the last two weeks, Phill Sledge, of Kaleen, has spotted ''hundreds of dead muttonbirds along the coast south of Broulee''.

According to Bryan, they are ''dying from starvation - their stomachs are full of pumice, leaving no room for any food''. It remains a mystery as to why the birds are ingesting the pumice and whether it is accidental (they are mistaking it for food) or deliberate (they are taking advantage of the pumice's abrasive nature to try to break down plastics and other debris caught in their intestines).

If you haven't made it to the coast to see the pumice phenomenon yet, there's no rush. ''It's not about to disappear,'' Bryan said. ''Pumice is very hard and takes thousands of years to break down.''

However, thankfully for those of us nursing badly stubbed toes, it isn't expected to litter the shoreline for more than a few months. ''Most of the pumice will either wash back out to sea or wave and wind action will leave it buried deep in the sand dunes.''

■ So what does a pumice raft look like? There aren't any images of the Havre Seamount pumice raft immediately after its creation, but sailor Fredrik Fransson photographed a series of extraordinary images as he sailed through a pumice raft following an underwater eruption near the Vava'u Islands in Tonga in 2006.

''As we sailed westward, the surface of the ocean inexplicably turned to stone,'' recalls the seasoned Swedish sailor. ''We looked out, and in front of us it was as if there was no more sea. It was like the Sahara, with rolling hills of sand as far as the eye could see.''

Fact file

Pumice stones: Pumice isn't just used as a cosmetic exfoliant (who hasn't vigorously rubbed a pumice stone on a rogue callus or a cracked heel?) but it is also used to stone-wash jeans and in some Pacific Island countries is broken down for fertiliser. Roman engineers also used it in the construction of the world's largest reinforced concrete dome - the Pantheon.

Did you know? The Havre Seamount eruption went unnoticed for over two weeks until an eagle-eyed tourist flying from Samoa to New Zealand spotted part of the pumice raft from a plane window.

Watch out for: Pumice pieces being sold at a coastal market, touted as ''rare volcanic rock''. Now, while it is clearly volcanic in origin, according to Dr Bryan, "the seamount spewed up trillions upon trillions of pieces" so pumice pieces are far from rare.

Word of warning: While finding a piece of volcanic history on the beach is fun, the pumice does pose a boating safety issue, with reports of it blocking and damaging water intakes for engine cooling systems on boats.


Old rattlers

This column's recent expose on wooden bridges of the south coast (Good ol' rattlers, December 28) struck a chord with many readers, including Peter McGann, who promptly checked out the Runnyford Bridge (between Nelligen and Mogo). He reports that it is ''in good condition and the view from the bridge towards the Clyde River is definitely worth seeing''.

While several readers, including Robert and Julie Gan, of Lyons, report the humped bridge spanning Wallaga Lake as their favourite on the coast, ''Wombat'' Maston reveals ''there is a forgotten bridge at Deep Creek near Bemboka - it has the old wooden charm, but it's easy to miss.''

Further, it seems that not all wooden bridge admirers prefer those that evoke a bygone era. For example, Nigel Chauncy, of Duffy, has a penchant for some of the newer bridges of our region. ''In particular, there's a wooden pedestrian bridge at the southern edge of Coila Lake at Tuross Head. It's less than five years old, but definitely one with character,'' Chauncy says.

Meanwhile, Alan Hume, of Greenway, reports ''there are so many wooden bridges scattered throughout this wonderful part of the country, and not just along the coast,'' citing the Tharwa Bridge as an inland example.

''I am so glad that commonsense prevailed in the rebuilding of the bridge at Tharwa, and that the ACT Government in its wisdom decided to retain the old style and not plump for a new concrete jobbie.''

Finally, Margo Saunders, of Weetangera, reckons the wooden bridge along Rosedale Road, near the entrance to Douglas-Apsley National Park in Tasmania ''must count as one of the most rickety in Australia''.

Saunders, who last travelled across the bridge in 2009, hopes ''it has since received some maintenance, as it was positively dangerous then''.


Email: timtheyowieman@bigpond.com or Twitter: @TimYowie or write to him c/o The Canberra Times, 9 Pirie Street, Fyshwick. A selection of past columns is available at canberratimes.com.au/travel/blog/yowie-man.