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London Bridge

A cache by tronador Send Message to Owner Message this owner
Hidden : 10/29/2008
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size:   other (other)

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Geocache Description:

London Bridge or Arch as it is now known, is a spectacular coastal feature along the Great Ocean Road. A board walk and viewing platform allows you to view the coast line and the arch safely.


London Arch is a natural arch in the Port Campbell National Park, Australia. The arch is one of the tourist attractions along the Great Ocean Road near Port Campbell in Victoria. This stack was formed by a gradual process of erosion, and until 1990 formed a complete double-span natural bridge. The arch closest to the shoreline collapsed unexpectedly on 15 January 1990, leaving two tourists stranded on the outer part: they were rescued by helicopter. No one was injured in the event. Prior to the collapse, the formation was known as London Bridge because of its similarity to its namesake. The soft limestone rock of these cliffs was formed between 10 and 25 million years ago,when the area was under the sea. The sea retreated and deep, vertical joints formed in the rock. Rainwater and spray percolated down the joints, dissolving the rock and widening the cracks. The sea advanced again at the end of the last Ice Age, reaching its present level about 6000 years ago. Since then waves have been attacking and undermining the rock, producing the cliffs that are present today. Harder rock remains as the headland. Waves continue to erode the softer underlying rock, causing caves and arches. The arch that you see today, was once joined to the mainland in a spectacular natural bridge,called London Bridge. It did have two arches just like its namesake, but in 1990, one arch collapsed into the sea. Eventually, the remaining arch will erode sufficiently that the overlying rock is not able to be supported causing it to collapse into the sea. In time this formation will become a single sea stack. Just like the Twelve Apostles, along this coast line. A sea arch is a natural arch or bridge made of stone that has been created through the process of land, wind, or water erosion. Of course, a natural arch is often made due to a combination of types of erosion. A natural arch or natural bridge is a formation of rock that includes a passage way in its lower half. Very often, arches are made by the meeting of two types of rock. The rock on at the top of the arch, which forms the bridge is made of a harder type of rock than what is on the bottom. If the bottom rock is a softer type of stone, it will erode away more quickly, thus leaving behind an arch. Natural bridges commonly form where cliffs meet the sea. In this instance, the formations are called “sea arches.” A sea arch is created when the natural erosive forces of the water break through a slice of rock and leave behind an arch.

To log this cache walk to the viewing platform and:
1.Estimate the height of the arch above sea level.
2.How many distinct layers of rock make up the headland around the arch?
3.What would cause the reddish appearance of the uppermost rock layer?
4.Take a photo of yourself in front of the sign showing London Bridge in the background.

Sources include:
www.australianexplorer.com/great_ocean_road.htm
www.fettes.com/shetland/arches.htm
www.wisegeek.com/what-is-a-sea-arch.htm www.britannica.com
Wikipedia Parks Victoria

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