|Mount Warning looking over the Nightcap Ranges|
How big was the Mt Warning/Tweed Volcano? It is certainly not a question that just jumps into ones head unless you love geology!
The traditional view by respected geographers such as Cliff Ollier is that Mt Warning is a remnant of a huge shield volcano that erupted during a time that was known as the Cenozoic (or Tertiary). The extents of the shield was from Evans Head in the south to Mount Tamborine in the North to Mount Lindsay in the West to somewhere out to sea to the east. It must have covered around 7 000 square kilometres in area and been almost 2 000m high. Ferrett (2005) gives its height as 2000metres and a diameter of about 100km. It was big. But I think it is wrong. Well, at least partly wrong.
The funny thing about scientific discovery is that once one is made once something is finally thought to be understood, contradictory information is seen as too hard to deal with. It is a kind of scientific inertia. Especially once the general public think something is true. For example, I've heard again and again that the Great Wall of China is the only man made object to be seen from space (it cannot be seen; whereas cities, irrigation channels, farmland and other objects are seen commonly). This is true too for Mount Warning/Tweed Volcano.
I've been able to find some 'forgotten' (but not long forgotten) research recently that I think turns things on its head. These are:
Masters research from Southern Cross University (when they had a geology department) by Cotter (1998) (the only online reference I can find is here but there is a copy of his thesis in the archives of Southern Cross University, which you can read under supervision only!), A journal article by Duggan and Mason (1978) here and another journal article by Smith et al (1998) here.
Can you put it all together?
I even think that Duggan and Mason (1978) are a little generous with the Lismore Basalt. I think that more of what they called the Lismore Basalt (from Mount Warning/Tweed Volcano) is actually Kyogle Basalt (from Focal Peak/Mount Barney). This makes the extent to the west much less. At a push Smith et al (1998) show that there are no Cenozoic basalts exist in the Evans Head area. But most significantly Cotter shows a even more:
1. basalts between Evans Head and Alstonville are different compositionally from the Lismore Basalt and are probably part of the Chillingham volcanics and therefore they are Mesozoic aged (much, much older than the Tweed Volcano.
2. the land form would have directed lavas away from the south and
3. most of the basalt in the Lismore/Alstonville area is likely to be twice the age at around 40 Million years and definitely would not have been part of the hot spot volcanism that formed the Mount Warning/Tweed Volcano around 23 million years ago.
This all shows that a lot of the recent volcanic geology of the area needs to be reviewed (Is there a 'Alstonville Basalt'). Was the basalt around Alstonville actually similar to basalts in the New England tablelands (such as the Maybole Volcanics) which were associated with the formation of the Tasman ocean? What were the southern extents of the Lismore Basalt after all?
*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.
* Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.
*Ferrett, R. Australia's Volcanoes. New Holland Publishers 2005.
*Learned Australasian Volcanology Association, 1998. Lava News, December 1998.
*Smith, J.V., Miyake, J., Houston, E.C. 1998. Mesozoic age for volcanic rocks at Evans Head, Northeastern New South Wales. Australian Journal of Earth Sciences V45