Red mountains and crescent bays of Freycinet Peninsula, Tasmania
Intro: Freycinet Peninsula is arguably the most popular tourist destination in Tasmania. Just look on any pamphlet for the island state and you will more than likely find a photo of the stunning (and appropriately named), Wineglass Bay. What makes Freycinet so beautiful can be traced back to the geology and geomorphology of the area. I recently did a multi-day hike along the Peninsula (i.e., the Freycinet Peninsula Circuit), which consists of a counterclockwise circuit, starting from Coles Bay and ending at Mt. Amos. In this post I will share some of the insights in the glowing red mountains and sparkling blue beaches that make this place so alluring.
Science Spiel: Glowing mountains and wine glass shaped beaches (Geology, Geomorphology)
Freycinet Peninsula is composed of large granite bodies. They are Devonian in age, and are a striking difference to the other main geological units that comprise most of Tasmania (i.e., the young, prominent Jurassic dolerite and the old, deformed Precambrian quartzite). There are two major types of granites, I-type and S-type. They are classified this way in regards to their molten source being either igneous (I) or sedimentary (S). The I-type granites are enriched in sodium and calcium, and have the mineral hornblende. S-type granites are depleted in sodium but enriched in aluminum, they typically have the minerals muscovite, biotite, corundum and garnet. On the Freycinet Peninsula, granites are mostly S-type, and they range from equigranular to porphyritic, with large K-feldspar crystals (Groves, 1967). In fact, the K-feldspar-rich composition of the granites is what gives them their characteristic red appearance, which appears to be amplified when the sunset light hits Mt. Amos and the Hazards mountains. Granites here are also more radioactive than other granites in Australian, due to significant amount of U and Th. This isn’t, however, a contributing factor to the famous red glow at sunset!
These granites have curved, domal surfaces which is a characteristic feature of granites called “onion skin” weathering (e.g., sugarloaf in Rio de Janeiro). This is caused by exfoliation from elastic expansion and contraction of the rock, which causes outer slabs “skin” of the rock to fall off, which exposes fresher surfaces that haven’t been discoloured yet due to weathering processes. Pre-existing joints and faults also get weathered out more easily, which aids in making and defining the rounded boulders.
Beside the rocks, the other remarkable landscape of Freycinet is the white sand, blue water, crescent-shaped beaches. Some of the most popular are Hazard’s Bay and Wineglass Bay. Bays are semi-enclosed bodies of water, commonly in a crescent shape (hence the characteristic “wineglass” shape), with calmer water than the surrounding ocean. This is due to headlands on either side of the Bay which reduces wind and blocks and refracts waves into the bay. The beautiful white sand that composes the beaches can also be attributed to the granite rocks, as the most of the quartz sand grains likely came from erosion of the quartz-rich granite bodies.
Final Thoughts: While the mountains at Freycinet aren’t as rugged as those in the southwest of Tasmania, the domal-shaped granites definitely hold their own magical allure. It isn’t a surprise why Freycinet is regarded as one of the must-see places in Tasmania. Freycinet National Park is easily accessible driving from Hobart, with only a short hike to the lookout of Wineglass Bay. I, however, also highly recommend the Freycinet Peninsula Circuit 3-day hike. Both are great ways to experience (and hopefully appreciate) the granite mountains and crescent-shaped beaches that define this place!
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