Tuesday, 2 July 2013

Pacific Islands on holiday to the North Coast

I often find some stories in newspapers touch too lightly on the subject of geology. These articles are often quite limited in scope and generally indicate quite simplistic notions of natural processes. This morning when reading a local newspaper The Tweed Daily News, I came across one such article. A link can to the article can be found here. This article is interesting because it covers some surprising points, but as Dr Malcom Clark an Environmental Geochemist from Southern Cross University implies in the article, there is more to the story than just a once-off beaching of pumice on Kingscliff Beach.

Pumice is a highly vesicular (aerated) volcanic glass. It is created when super-hot, highly pressurized rock is violently ejected from a volcano, especially those found in volcanic island arcs which are near active subduction zones. The unusual foamy feel of pumice occurs because of simultaneous rapid cooling and rapid depressurization. During the eruption the air bubbles are frozen in the rock. The amount of air trapped means that pumice usually has the unusual property of a rock being able to float on water.

If we work backward in time from the Tweed Daily News article a story starts to emerge on how the pumice on the beach got there. The first thing to note is that there are no active volcanoes on the Australian mainland or close to the eastern Australian coast. So, the pumice must have been brought in from somewhere else. Pumice has been common on Byron Bay beaches for the last few weeks ever since winter storms gave a good battering the coast in June. But a large amount of Pumice was also observed on the Queensland sunshine coast in April following late summer storms and the tail ends of cyclones. The storms force floating materials like rubbish and pumice onshore. This gives a clue about movement. It has taken a month or two to travel down the east coast on prevailing currents such as the south moving Eastern Australian Current. But there are no active volcanoes in Queenland either.

Bryan et al (2004) published an interesting article in Earth and Planetary Science Letters on pumice that was washed ashore all down the east coast of Australia in 2002. Here lies more of the answer. Bryan et al (2004) demonstrated that the pumice rafts were transported a vast distance across the Coral Sea and South Pacific Ocean, taking about almost a year to complete its trip on the prevailing currents and winds (the pumice was even blown backwards at one stage by a tropical cyclone). Surprisingly the 2002 Pumice landfall came from the Tonga area (North of an island and seamount chain that stretches to New Zealand called the Kermadec Islands), which is a long way away! Between the Kermadec Islands and Australia lies the Solomon Islands, Vanuatu and Fiji which all have active volcanic systems.  However, The pumice that washed ashore in 2002 was erupted in a submarine volcano (underwater) un-excitingly named Volcano 0403-091 from the Kermadec Islands and swept past all the other islands.

As for the current pumice landfall, in the last year there has been several eruptions of island arc volcanoes the Vanuatu islands, but significantly in July 2012 there was a major eruption of pumice from the vicinity of the Havre Seamount in the Karmadec Islands (Smithsonian Institute 2012). The time between eruption and East Australian landfall is interesting because it is similar to that for the 2001-2002 event discussed by Bryan et al (2004). More recently in 2012 an article was published (Bryan et al 2012) that demonstrated that rapid and long distance movement can be a frequent occurrence. So, maybe the pumice on our beach today this is just a little bit of history repeating – a bit of a pacific volcano on a holiday to the north coast of New South Wales.


Scott Bryan sent me this email yesterday. Being so informative I thought I should post it here.

Hi Rodney,
...I was actually at point lookout (nth Stradbroke) today collecting the pumice. The pumice is indeed from the Havre submarine eruption in the Kermadecs last year. There is a good summary of the eruption and discovery of the pumice rafts at the global volcanism program of the smithsonian institution (USA) at www.volcano.si.edu. 
This pumice is distinctive in being white when fresh; there is also a lot of grey/dark grey pumice at north stradbroke which is from tonga and the previous eruptions I have published on. It has been eroded out of the beach dunes.

The main influx along our shores began in mid-late march, continuing up to early May. There has been a bit of a break, but with the windy and wild weather this last weekend, some more pumice has come in, as well as probably reworked material (abraded and cleaned of attached biota) which seems to be what has washed up at Kingscliff. Newly washed up pumice will be covered in a black or dark green slime (Cyanobacteria) and be loaded with lots and large goose barnacles. You will also find on closer inspection, some molluscs, bristle worms (feeding on the barnacles), bryozoans, hydroids, anemones. Look up Denis Riek and his web page www.roboastra.com - he has taken some fantastic close ups of the pumice and biota found on it at Brunswick Heads.

This pumice has travelled about 3000 km in 8-12 months. We have observed it as far north as Heron Island.

Let me know if you need more info.

I would appreciate further reports of any new strandings as I have a Masters student beginning her research on this pumice and the attached biota. New strandings give us a temporal perspective as the biota mature and diversify with time and also begin recruiting species locally.


*Bryan, Scott Edward, S., Cook, Alex, Evans, Jason, Hebden, Kerry, Hurrey, Lucy, Colls, Peter, Jell, John S., Weatherley, Dion, & Firn, Jennifer (2012) Rapid, long-distance dispersal by pumice rafting. PLoS ONE, V7.
*Byran, S.E., Cook, A., Evans, J.P., Colls, P.W., Wells, M.G., Lawrence, M.G., Jell, J.S., Greig, A. & Leslie, R. 2004. Pumice Rafting and faunal dispersion during 2001-2002 in the Southwest Pacific: record of a dacitic submarine explosive eruption from Tonga. Earth and Planetary Science Letters V227.
*Smithsonian Institute 2012. Havre Seamount. Bulletin of the Global Volcanism Network. Smithsonian Institute. September 2012.

1 comment:

  1. Yes there was a lot earlier this year at Casuarina Beach, NSW. Not a lot to report right now though. Thanks for the article btw, it's great to learn about our local geology.