The Bay of Fires on Tasmania's East Coast has recently been rated by Lonely Planet as one of the hottest tourist destinations on the planet and it's not hard to see why. The combination of white sand beaches, blue waters and rounded granite boulders with orange colouring which bring people to this area are the subject of this earthcache.
The famous orange colour of the granite boulders in this area is actually due to lichen and is not part of the rock itself. The granite which forms these outcrops is known as a Devonian Granitoid and was formed around 380 - 400 million years ago during a period known as the Taberraberan Orogeny. During this time, tectonic plates were stretched and folded, allowing the molten granite to intrude. Outcrops are common along the North East Coast of Tasmania from the Freycinet Peninsula in the south through the Bay of Fires and northwards to the Bass Straight Islands, such as Flinders and Cape Barren Islands and even as far as Wilson's Promontory in Victoria. As the granite has become exposed, it has weathered and eroded creating the formations and beaches we see today. This granite has a very high quartzite content, which is responsible for the famous whiteness of the sand in this area, which contributes to the spectacular blue colour we see in the water on calmer days.
As the granite intrusions cooled and shrank, cracks were formed and later magmas were forced into these, cooling at different rates, forming deposits which have different physical characteristics to the surrounding rock. The action of water and wind erodes these rocks over time, with the resulting sand speeding up the process. Variations in hardness and cracks mean that some areas are eroded more quickly, or the abrasive action of water and wind, especially when carrying sand, result in the shapes we see today.
The published coordinates will have you at a particularly large example of one of these cracks which has been subsequently filled by magma, resulting in a seam of rock with different characteristics to the surrounding mass. There are a number of these around the outcrops, but this is a particularly striking example, which is visible from the protected area beyond the fence, running all the way down the rock into the sea. Presumably it continues in both directions, but these are hidden.
To claim this cache you need to contact me, preferably via the Geocaching.Com messenger and provide answers to the following questions:
Please note: There will be some days when it may be hazardous to be in certain areas of this formation. The lichen-covered areas of these rocks will be slippery if wet, either from rain or spray. You do not need to place yourself in danger to answer these questions, the crack is visible from areas which are not subject to waves or spray.
1: Please describe the appearance of the seam of rock and how it differs from the surrounding rock mass. This is not an open crack, but is filled with rock of different appearance.
2: Rocks with differing hardness weather at different rates. For this seam of rock and the other similar ones nearby, which is harder, the main mass of rock, or the deposit in the crack ? How can you tell ?
3: Typically, the boulders and outcrops for which the Bay of Fires is famous, have a rounded, smooth shape due to weathering and erosion by the action of the sea. However, this is not always the case. Near the published coords, behind you if you're facing the sea, are a number of rocks which are quite different in shape. Please describe these shapes and the process you think may have caused them to be different.
4 (optional) : A photo of the rocks, the sea and waves, or just the general area would be great as a way of recording the changing seasons, but please don't post pictures which may be spoilers (eg, close-ups of the seam, or the differently weathered rocks)).
Please note, I will delete logs if no answers are sent.