The High Island Geo Trail, at the High Island Reservoir east dam, presents enchanting views of the lake and rolling peaks, with magnificent giant columnar rocks dominating the landscape. This is the best location to observe Hong Kong’s world class hexagonal rock columns at close range. This site also features other interesting geological structures and features like faults, distorted columns and an intrusive dyke. The trail is an easy level walk, suitable for all types of visitors, with interpretation signs and basic countryside facilities.
You can also visit the Volcano Discovery Centre of Hong Kong UNESCO Global Geopark at Sai Kung Town to get more information and understand the past volcanic activities in Hong Kong.
A Giant Pipe Organ - Po Pin Chau
Looking toward the sea from East Dam, Fa Shan is cut into two parts;
the one being separated is Po Pin Chau, which is a type of the sea
abrasion landscapes - sea stack. Po Pin Chau was once part of Fa
Shan, but years of wave impact and erosion separated it. The rock
stacks on the shore of Po Pin Chau tower almost vertically over the
sea. The rock face looks just like a giant pipe organ.
S-shaped Hexagonal Rock & Columns and Intrusive Dyke
About 140 million years ago, when the columns were still in a semi-plastic state, they were distorted into an S-shape under the influence of earthquakes and regional subsidence. The distorted area of the rock columns is the most vulnerable. During geological processes, magma intruded along the weak line of the columns and cooled to form an intrusive dyke, which is about 40 million years younger than the surrounding rocks.
Rock columns elsewhere are usually made of dark grey basalt with low silica content. By contrast, the rock columns in Hong Kong are light-coloured, silica-rich, rhyolitic volcanic rock. The columnar joints are mainly pentagonal or hexagonal. It is estimated that the columns cover an area of over 100 km2 (including submerged areas), with an exposed height up to 100 m, a total thickness of 400m and an average diameter of 1.2 m. The rock columns have features of both tuff and lava, but there is still no consensus among geologists on the material that formed them.