This Earthcache is of a feature I didn't know was in Australia never-mind Tasmania, the only place I have seen this type of thing before in the north coast of Antrim, Ireland!
On to this Earthcache, while you can observe dolerite formations all over Tasmania the one at this site are particularly interesting as you can view them so easily.
Formation: During the breakup of Gondwana, dolerite magma was injected as subsurface dykes and sills (sheets), across most of Tasmania. As the magma cooled and crystallised, regular vertical cracks propagated through the sills, forming columns.
Significance: Dolerite is unusually widespread in Tasmania, and is appropriately referred to as ‘the rock that made Tasmania’. It forms the iconic ‘organ pipes’ landscape above Hobart, as well as on the Tasman Peninsula and the Central plateau.
The hexagonal, prismatic column shape is termed columnar jointing. Dolerite forms this way because the magma cooled from the outside toward the centre surrounded by more or less consistent temperatures. These joints radiate outward from the centre of each column, which themselves form perpendicular to the flow base of the source magma (or lava if the rock was extruded at the surface, such as basalt).
The Jurassic dolerites of Tasmania form just a small part of the Ferrar Large Igneous Province (FLIP); a 3 500 km long linear belt of tholeiitic rocks which extends along the Transantarctic Mountains of Antarctica and into South-East Australia (Elliot and Fleming, 2004). The FLIP was emplaced during the early stages of Gondwana break-up from a source located in the Weddell Sea region (a part of the Southern Ocean, located above what is now the North-West Coast of Antarctica), with magma transport controlled by an early Jurassic zone of extension (Figure 1) (Elliot and Fleming, 2000, 2004).
Gondwana reconstruction showing distribution of the Ferrar Large Igneous Province and the inferred source of the Ferrar tholeiitites in the proto-Weddell Sea region (Weddell Triple Junction). From Elliot and Fleming, 2000. CTM – central Transantarctic Mountains, EWM – Ellsworth-Whitmore Mountains Block, ENZ – east New Zealand, KD – Kirwans dolerite, MEB – Maurice Ewing Bank, NVL – north Victoria Land, SVG – south Victoria Land, TI – Thurston Island, WNZ – west New Zealand.
"Tasmanian Dolerite" by Perinne Tyler is in the Public Domain
To claim a find on this earthcache please complete the following tasks and send me the answers to the following questions.
- Measure the width of one of the columns. Are all the columns a similar width? Why would this be so?
- What shape are the columns? Why do you think they are this shape?
- How do you think these columns were formed?
- Take a non-spoiler picture of yourself at GZ and include it in your log to prove that your team have attended the site.