The Tweed Valley in far northeastern N.S.W. Australia is a dramatic part-caldera with a central 1km peak – Mount Warning – and a flat plain in the north east. ‘The Tweed’ is most often described as being the eroded remains of an ancient massive volcano, an interpretation of the Tweed Valley’s morphology which leaves some perplexing questions, such as:
- How can water have eroded the north eastern valley floor so flat with no major channels besides the Tweed River? Water leaves channels.
- If water did wash away the volume of the volcano down to what we see today, why do the monoliths on the plains like the one at Eviron Rd – or the impinging ridges closer to the sea – not display any noticeable extra erosion on their ‘upstream’ flanks?
- How could water have eroded the walls of the amazing Limpinwood Valley and not left a massive hole in the ground!?
- Why are there so many topographical patterns on and around Mount Warning and the Tweed Valley? In the following maps I will point out some of them.
Several striking patterns appear on this terrain view from Google Maps. In the west a range associated with a sweeping series of leichtenberg-type* ridges and associated valleys forms a regular curve extending through Mt. Barney (circled) and onwards by extension to Mt. Warning.
Over in the Tweed Valley, one yellow line extends through twin parallel fractures on the bald peak of Mt. Warning and north across parallel ground features on the Tweed Valley floor and in the Springbrook N.P. and an extended ridge system north to Ormeau.
The perpendicular SW – NE line on the right goes in a straight line through a large gap in the SW caldera wall, the path of the Tweed River (between Hattons Rock and Mt. Nullum) and out onto the flat plains in the north east. N.B. the hexagonal rock pillar piles at Fingal, and Tropical Fruit World / Cudgen..
*As a side-note about liechtenberg-type ridges and associated valleys, even if receding erosion causes them, how is it that the more durable rock exposed has been deposited in those formations?
In this picture the full circle around Mt. Barney should be dotted. Anyway a ridge line runs from the lip of the Mt. Barney caldera (itself remarkable topographically) and over a gap and up to the rim of the Tweed caldera. I have very lightly highlighted around two areas adjacent to where the ridge lines meet. In both areas there is some landform incursion inot the caldera. The southern highlighted area is The Pinnacle and can be walked out onto**, and the northern triangular rock formation is Limpinwood N.R. The line on the right is a re-iteration of the ‘fracture lines’ pattern from the tip of Mt. Warning across the valley floor and into Springbrook N.P an so on.
Obviously over enormous time scales ‘anything can happen’ in the forward motion of geographical processes. However the topography of the Tweed includes many symmetrical patterns and regular shapes besides those illustrated above, indicating that perhaps more than lava and gravity were involved in the formation of its landforms….
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