Sea caves, blowholes and coastal arches are formed when waves erode a layer of rock under a harder layer on a coastline cliff. In time the erosion forms a tunnel through which the water rushes as the tide rises and falls. these tunnels can be above or below the waterline.
If the tunnel reaches a softer layer of rock above it, the constant erosion causes this soft rock to erode and eventually collapse into the tunnel. the constant ebb and flow of the tide removes the rubble, leaving behind it either an arch, or a blowhole if the tunnel is significantly long.
There are some beautiful spots around the Tasman Peninsula, as well as some unique and amazing rock formations. Eaglehawk Nest is a good place from which to see the beautiful coastal rock formations, one of which is The Blowhole. Australia's biggest blowhole, it is situated close to the entrance point to the Tasman Peninsula.
Also in The Tasman National Park, Maingon Blowhole can be reached via a walk which traverses the Tasman Peninsula. The sea cliffs on this section of the coastline are amongst the highest and most rugged in the world. On the journey towards Crescent Beach there is a formidable gulch that feeds Maingon Blowhole which is very deep. Attempts to see the bottom should be avoided without the use of protective ropes due to the unstable surrounds - the water can be heard crashing far below, however.
The Bechino blowhole, on Tasmania's east coast, is located near the Esplanade Reserve. It is one of Australia's most reliable blowholes in that it blows in most weather conditions. Nearby is also the Rocking Rock, 80 tonnes of rocking granite, which has been rocking for thousands of years.
Similar in size to Tasman Arch, this natural bridge is somewhat smaller but still quite dramatic. The arch is located near Waterfall Bay and can be viewed from the walking track from the Devils Kitchen carpark to Waterfall Bay. It is equally as impressive from the ocean side.
There are many sea caves (above and below the waterline) and rock arches along the east coast of Forestier and Tasman Peninsulas and Bruny and Tasman Islands. Those caved out of the cliff face by the forces of nature are not visible from land, and must be visited by boat. A number of cruises ply thesec waters, but for a more intimate look and exploration, nothing beats a kayak. Photo: Cape Queen Elizabeth.
A natural arch which is an enlarged tunnel running from the coast along a zone of closely spaced cracks and extending inland to a second zone that is perpendicular to the first. The roof at the landward end of the tunnel has collapsed but the hole is too large and the sides are too high to form a blowhole. The tunnel was produced by wave action. The arch ceiling is 52.7 m above sea level. Most people only see the land-side view - a boat trip alongside the coastal cliffs offers a different perspective of the arch.
The 60 metres deep Devil's Kitchen has been formed by a similar process to that which has created Tasman's Arch. Basically, if an arch like Tasman's Arch collapsed, it would lead to the creation of a landform like the Devils Kitchen.
Beyond the Port Arthur historical site is Maingon Bay and perhaps the most remarkable feature of them all, the appropriately named Remarkable Cave. It is remarkable not only for its unique form, but also because its opening, when viewed from the observation platform, is the shape of Tasmania. The cave is today a deep rock bridge carved out of the sandstone cliff face, but it was once a deep cave. The viewing platform at the bottom of steep stairs is where the back of the cave collapsed.
The rugged southern coast of Tasmania is some of the most scenic in the country. Coastal features of every size, shape and description abound, including numerous natural bridges. South Bruny Island has a number of bridges including the arched Bridge. A unique feature off the coast is Bridge Rock, a craggy island which has a sea channel carved by nature through its centre.
There is a blowhole near the northern end of Blackmans Bay beach, to the south of Hobart, which in reality is more like a large rock arch where waves can be seen coming in and crashing on the rocks. There are numerous cliffs and viewpoints along Blowhole Road.
Arch Rock is small sandstone island at Ninepin Point Marine Reserve a few kilometres east of Verona Sands (Huon Valley), named for the cave that forms an arch in its centre and it’s a notable geological feature as well as being an interesting dive. Diving in the tannin waters of the reserve is an iconic Tasmanian dive experience. The waters of the Reserve are subject to high levels of tannin from the nearby Huon River. Less dense tea-coloured fresh water overlays the colder sea water and filters out light, which leads to some marine life being seen in much shallower waters than otherwise.
One of the natural wonders to be found on the coasts of South Bruny Island is Breathing Rock, a cavern in the rock face near water level that fills with air as the waves wash out and then as the waves washed back up into it, the air is forced back out with a huge spray. Those who travelled the south and south eastern coast of Tasmania by kayak agree that Bruny Island's Breahing Rock is impressive but is nothing compared to the huge 'breathing rock' on DeWitt Island in the Maatsuyker Group on the south coast of Tasmania (below).