User:Abrow/sandbox

Ancient Lumps on the Somerset Landscape Whether entering Somerset from the east via the Brisbane Valley Highway or the south via The Gatton-Esk Road, it is hard not to notice some unusual geological features. On approaching the western end of The Wivenhoe Dam wall, two of these little features can be seen ahead: Mount Hallen and slightly behind it, more to the south, Mount Mulgowie. There are conflicting reports of the heights of these mountains. The standard Somerset Region Map, published by Cottrell Cameron& Steen Surveys, edition 2/2010, indicate that Mt Hallen is 388 metres from sea level and that Mt Mulgowie stands at 334 metres. However, another source states that they are 191.65 and 315.75 metres in altitude, respectively! The most odd, protruding, little mountain one can also see from the dam wall, but more noticeably, stuck in the middle of the Brisbane Valley, is Mount Tarampa. On the Somerset Regional Map, it doesn’t even register a height but it is a little protrusion of about sixty metres above sea level, not an impressive height by any means, yet, cute as a button!

These three mountains form a triangulation with an acute angle pointing due south east, Mount Tarampa being the sharpest point, positioned as it is, in the middle of the Moreton Basin

Alternatively, as one is travelling due west on the Warrego Highway, towards Toowoomba, these lumps never cease to amaze…how did they end up there, lonely and isolated as they are, like little pimples on the landscape, away from any mountain ranges? On first appearance, they don’t look anything like the very obvious volcanic plugs of the Glass House Mountains further north, all of which are smaller than two of our ancient lumps on the Somerset landscape. It is a wonder that little Mount Tarampa was even accredited with the title of “mountain” at all! The physiography of the whole Ipswich and Brisbane 1:250000 sheet areas is divided into:
 * Mountains and Ranges. In general, they are 150 through to 939 metres in elevation, (Mount Mistake, 25 kms due south of Laidley, being the highest surveyed point in the area). In the Somerset Region, the highest point appears to be at Mt D’Aguilar on the D’Aguilar Range which was formed by the “Neranleigh- Fernvale Beds”.
 * Plateaux. The Darling Downs Plateau is the largest in the area, covering appx.1000km2 and is situated west of The Great Dividing Range, whilst there are smaller plateaux in the vicinity of Mt Tamborine, due south east, near the Gold Coast and Mt Mee, just east of the Somerset Region.
 * Areas of high relief. These are isolated peaks such as Mt Brisbane with an altitude of 678 metres (682 metres on the Somerset Region map); Bluff Mountain, 520 metres and Flinder’s Peak at 680 metres.
 * Areas of moderate relief. The relief areas between 120 and 300 metres are associated with the sandstones of the “Bundamba Group”.
 * Areas of low relief. These refer to areas of less than 120 metres in altitude and occur in the valleys of Lockyer Creek,the Brisbane, Logan, Caboolture, and North& South Pine Rivers.

So the three mountains that so obviously blot the landscape in the Brisbane Valley, to which this article is referring, fall in the category of moderate and low relief areas, and don’t rate a significant mention in the Geological Survey of Queensland report, compiled by R.J Allen( Chief government geologist at the time of its publication). This writer is still intrigued by these features, nevertheless. But wait! An acknowledgement has surfaced. It seems highly likely that the forces that produced Mt Hallen, Mt Mulgowie and possibly even Mt Tarampa, are associated with something called “Brisbane Valley Porphyrites”.From memory, porphyry is a volcanic by-product and therefore, an igneous rock. Porphyrites are of a similar composition, ie, crystals set in a fine-grained ground mass. The composition of these are  apparently well jointed and form blocky outcrops and are spherically weathered. Does that mean in the same way that our above mentioned mountains are shaped? If only reports could use laymens’ (and womens’) terms. “The Brisbane Valley Porphyrites” intrusions occur in the zones that had maximum disturbance along the “Esk Formation”. If one reads between the lines, it sounds as though there may have been little volcanoes in the area, but they are so eroded and ancient that the plug shapes are now defunct(?)

Whilst Mount Wycheproof of the Terrick Terrick Range in western Victoria is claiming the title of the smallest registered mountain in the world( 5), it can be contested, and probably will, by the LGA of the Somerset Region. Since the registered height of Wycheproof is 43 metres above the surrounding plains but not from sea level, it is likely that Mount Tarampa, standing at a height of 59.3 metres above sea level, is indeed the smaller of the two. Chances are that it could earn its fame and a position in the limelight by being the smallest mountain in the world! What a scoop that would be for The Somerset Region, and who wouldn’t like to be photographed next to it!

What else can our little mountains offer? Wait and see. There’s more to come, a promise from a frustrated, would-be geologist.

(1)	Mount Hallen QLD@ExplorOz Places Mount Mulgowie QLD@ExplorOz Places (2)	Geological Survey of Queensland Report nr 95, Geology of Ipswich and Brisbane1:250000 sheet areas/ by L.C. Cranfield, H.Schwarzbock, R.W.Day. pg. 113 (3)	ibid pg. 12 (4)	ibid pg. 108 (5)	Wikipedia on Answers.com Mt. Wycheproof (6) 	http://maps.bonzle.com By Camilla Brown. 06-2012.