The pluton encompasses large outcrops of medium-grained, uniformly equigranular granite exposed at Chung Hom Kok and Stanley Peninsula, to megacrystic coarse-grained at Po Toi Island.
Coastal erosion features, such as geos and sea caves, are prominent in the area where Po Toi Granites present due to prolonged exposure to monsoon wind and wave actions with long fetch.
Geo is an inlet, a gully or a narrow and deep cleft in the face of a cliff. They are created by the wave erosion of cliffs along lines of weakness caused by intruding dykes, faults, joints or by earth crust movements. Where those lines of weakness intersect the cliff face then linear zones of fractured rocks in between are more vulnerable to wave erosion. Long and narrow slots can develop when a notch is carved by the wave action at the base and the rocks above collapse. At headlands or cliffs, wave erosion is most concentrated because of wave refraction.
The earthcache locates at the headland of Chung Hom Kok, where you can find a geo and a small cave at the base. The erosion action may have stopped when the land mass rose above the sea level.
To log this earthcache, you need to complete the following tasks and send the answers to me:
1. Examine the Po Toi Granite at ground zero. Describe its composition, grain size, colour.
2. Based on the geographical location at ground zero, explain how the geo and the cave were formed.
To get to the GZ, go to Chung Hom Kok Park rest area (Reference Point 1) next to Cheshire Home, take the hidden stairs (Reference Point 2) at the corner and get to the search light position (Reference Point 3) and find the steep descend on the left side. Some rock climbing is needed and so take absolute care. Strongly advise to go on dry and calm days only. Also watch that your mobile phone may switch to roaming in the area.
For geocacher's interest, the cave at GZ is one of the three Cheung Po Tsai Caves in Hong Kong. Cheung Po was an infamous pirate in the early 19th century active along the coastal area of Guangdong . At some stage he owned a fleet of 300 vessels and with more than 70,000 followers. It was rumoured that he had hidden his treasure in some of the sea caves and GZ was one of those. Obviously there is no trace of any treasures these days and it becomes a dwelling place of bats and mosquitoes.
Safety warning - Don't go solo. Strongly advised to be accompanied when entering the cave. Need strong flashlight. Also avoid times of high tides.