Friday, 1 June 2012

A warning about Mount Warning

Here are some common quotes about Mount Warning:


"World Heritage listed Mount Warning (Wollumbin) is the remnant central plug of an ancient volcano." 
"The Mount Warning volcano was a huge shield volcano."
"Considered the central magma plug, Mt Warning and a system of ring dykes, being extremely hard rock, have resisted erosion, and dominate the valley landscape."
"Mt Warning, Wollumbin, the cloud catcher, is the basalt plug of the world's largest and oldest extinct volcano. "
"Now, Mt. Warning is the first place that that the sun hits at sunrise… the highest point in New South Wales….almost the highest in Australia!"

These are quotes typical of tourist and even educational resources. They are quite definite and the comments makes sense, mostly. There are also some points of view that I espoused for a long time... Except aspects of each of the quotes are technically wrong and in some cases completely wrong. Like my post on the "erosion caldera" something that is technically incorrect has become general knowledge. It is a little pedantic of me, but it is one of my hobby horses... so what is technically wrong with the quotes above?

Western face of Mount Warning (composed of syenite).
One of the ring dykes is visible in the foreground
and Mount Uki and the Pacific Ocean in the background

Interestingly, Stevens et al (1989) and earlier authors noted that the rock composition of the intrusions that make up Mount Warning (the Mount Warning Complex) is different from most of the lavas (The Lamington Volcanics) that exist in the region. It is also slightly older than most of the lavas. Geologically speaking the age difference is not huge at only about 2-3 million years, but still significant enough.

It is apparent from Smith & Houston (1995) and other authors that much of the rhyolite lavas that remain of the Lamington Volcanics were not erupted from the central area now the site of Mount Warning but from vents on the flanks. Given the coverage of the mafic components (the Lismore Basalt, for example) it is more difficult to identify any vents.  

An idea has been raised by Cotter (1998) which questions the volume of lava that was erupted from the Tweed Volcano. It is known that the Palaeozoic aged meta-sedimentary rocks of the Beenleigh Block, called the Neranleigh Fernvale Beds and the Mesozoic aged Chillingham Volcanics and Clarence Moreton Basin were not domed upwards by the underlying magma except a little around the Mount Warning Complex itself. However, other areas such as the nearby slightly older Focal Peak Volcano have been lifted by the Cenozoic aged volcanism. But in the case of Mount Warning, Cotter (1998) felt that lithology, the remnants of the rhyolitic lavas, the pre-existing Chillingham and Alstonville Volcanics was the main control on the geomorphology, not as suggested by others the volcanism that formed the shield volcano itself.

The idea suggested by Cotter (1998) has significant implications for the size of the Tweed Volcano. The volcano is considered the biggest by far of its age in eastern Australia. It appears likely that the extent of the shield volcano is not as great as originally thought. The underlying Chillingham Volcanics would have been an existing mountain range and therefore reduced the thickness of the Tweed volcanic pile and the Alstonville Basalts would have reduced the southerly extent. I think that when you add to this the idea that the rhyolite units have erupted away from Mount Warning, but instead from flanks on the volcano, the volume of lavas from the Tweed Volcano may actually be more in keeping with the other intra-plate volcanoes in Eastern Australia. It was also possible that before it was eroded into the present shape (which implies a central shield type volcano) it may have looked more irregular than we imagined...

But don't get me started on the comments about the biggest volcano in the world and the highest point in New South Wales!!! What were these people thinking?!

...but does any one want to talk down something that was presumed to be huge, just to something large? Emotionally, many (including myself) have an emotional attachment to the beauty and wonder of the Tweed Volcano, sometimes it is hard to take a step back and consider it is not quite as fabulous as originally thought, but what we see is still stunning... and it is still very, very big. To put that in perspective I think that even the small volcanoes in the region are stunning. We don't need to exaggerate something for it to inspire us.

Bibliography/References:

*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University. 
*Smith, J.V. , Houston, E.C. 1995. Structure of lava flows of the Nimbin Rhyolite, northeast New South Wales. Australian Journal of Earth Sciences V42(1) p69-74.
*Stevens, N.C., Knutson, J., Ewart, A. & Duggan, M.B. 1989. Tweed. In Johnson, R.W. (ed). Intraplate Volcanism in Eastern Australia and New Zealand. Cambridge University Press.

5 comments:

  1. Good to read this Rod. I love Mt Warning for its present beauty as a landmark and for the vegetation surrounding it, but it's also good to know some more of the details.

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    1. Hi Sunshine,

      Thanks for visiting and commenting again. The forests are amazing too, you are right. There is so much beauty in the world, seen and unseen.

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    2. Hey good read would you be able to tell me what gems can be found around mt warning thank you

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    3. Hi Anonymous,

      I'm not much of an expert on gem stones but I know there is some around the Mount Warning area - though these are most often found around the rim of the valley, for instance in the Uki area you can find 'thunder eggs' and sometimes agate.

      I will try and get a blog post up before the end of the year that might help.

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  2. Georgica Rhylolites on the southern flanks of what would have been the Mt Waring volcanic caldera are evident in the dykes stemming from the main vent.

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