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Inspired as one of the best dive stites in the world this Earthcache is sited on The Brothers Islands in the middle of the Red Sea. These two pinacles of rock rise from the sea bed many hundreds of metres deep. as a result they are world renown for the quality of the hard and soft corals and the number of large fish that come here to feed including many shark types.
The Red Sea was formed by Arabia splitting from Africa due to movement of the Red Sea Rift. This split started in the Eocene and accelerated during the Oligocene. The sea is still widening and it is considered that the sea will become an ocean in time. Sometimes during the Tertiary period the Bab el Mandeb closed and the Red Sea evaporated to an empty hot dry salt-floored sink. Effects causing this would be: A "race" between the Red Sea widening and Perim Island erupting filling the Bab el Mandeb with lava. The lowering of world sea level during the Ice Ages due to much water being locked up in the ice caps. Today surface water temperatures remain relatively constant at 21–25 °C (70–77 °F) and temperature and visibility remain good to around 200 m (656 ft). However, the sea is known for its strong winds and unpredictable local currents. In terms of salinity, the Red Sea is greater than the world average, approximately 4 percent. A number of volcanic islands rise from the center of the sea, most are dormant, but in 2007 Jabal al-Tair island erupted violently.
Importantly these islands are unique geographical features formed as a result of such volcanic activity that forced magma to the surface cooling to form two distinct but interconected new land masses. The landmasses are over 60miles offshore and experience significant cold water upwellings and offshore currents which combine to produce ideal conditions for coral growth and visiting feeding sealife.
It is this second geographical feature that has given rise to the 'growth' of the landmasses with Big Brother displaying growth patterns most significantly; from the sea surface upwards a clear dark coloured basalt layer is visible which formed from the cooling magma. This igneous rock formation has been cooled by water and demonstrates a particular extrusive formation as result. Above this, the desert coloured layer, is formed completely of coral growth.
This is one of the few examples where coral growth above basalt can be directly observed.
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Visiting boats are permitted to moor in the lee of the island and the resident lighthouse and army staff (two of each) welcome visitors to drink tea, smoke shisha and visit the lighthouse. The views from the top are outstanding and reveal the full extent of the reef system that exists here forming the landmass. When you walk around the island you can see the size and scope of the coral pieces that form the top level of the land.
Whilst on the island you are encouraged to conduct some small CITO work helping the residents maintain this unique geographical feature.
The residents will welcome you to climb the lighthouse from where you have extensive views of the whole of the island and its underwater coral reefs that surround the landfall before dropping to the depths.
To claim this cache you need to answer a couple of questions and undertake a task:
Estimate how far above the level of the sea the basalt layer extends just to the right of the jetty?
Observe the type of basalt and categorise it as intrusive or extrusive rock and explain how you come to this conclusion from what you see and why it occurs at this location. This is best achieved from the land where close observation of the rock is possible.
Optional: photograph you/ your GPS at the basalt layer, or coral surface layer surrounding the lighthouse.
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