«Sai Kung Geopark Tour Commentary Special Thanks: Agriculture, Fisheries and Conservation Department and San Cheung for their invaluable support The ...»
During the late Jurassic to early Cretaceous (143 mya - ~140mya), the volcanism here was violently ongoing by four stages. Eventually the emptying of underground magma chamber led to the collapsing of crater and created the largest caldera in Hong Kong. It is sitting out there underneath the east sea nowadays after sea level rise and we will be travelling above it. The caldera area covers the several islands we are going to visit as well as the East Dam area of the High Island.
Sharp Island The ancient volcano had disappeared after million years of weathering and erosion, however, some important traces have been left on Sharp Island. And further explaination …e.g. edge of the ancient volcano. This island is close to the Sai Kung Township. It takes only 15 minutes boat ride to reach from the Sai Kung pier. Sharp Island is one of those inhabited islands with few villages.
Once there was even a Water Fun Park built here providing people with various games at the beautiful Kiu Tsui Beach(橋咀泳灘) making this island becoming the recreational focus in the area.
In addition, Ha Mun Bay Beach is another white sandy beach which is always crowded during Summer days. Nowadays area around Kiu Tsui Beach is designated as a Geo area of HK Global Geopark demonstrating various kinds of volcanic rocks and an amazing landscape such as tombolo (tombolo is a natural sandy bar connecting 2 islands or an island to mainland, emerge during low tide). Lots of people find it really interesting to come and see those Pineapple Bun rock - an interesting pictographic rock and to walk on the tombolo during low tide. Visitor can follow the Geo-trail which will take roughly one hour to complete. The trail comes with Page 24 information panels in picture and text from which visitors could pick up a free lesson on the geology of Sai Kung.
Travelling toward the centre of the ancient volcano from the edge. See the islands are made of the volcanic materials, the rock type is the same over the island on Sai Kung Sea, but in the volcano centre, it forms closed pack columns, only a few columns can be found toward the edge.
Columns in poor shape can be found at the south and some other area of Kau Sai Chau.
Kau Sai Chau (滘西洲) This is the biggest island out here in Sai Kung. It has a indented coastline and many deep sheltered bays which was truly some good habitats for marine creatures. At the gap between this island and Jin Island there is an old fishing village since the Qing Dynasty. Once the population was up to 400 people and is only about 50 left now. Northern part of the island has been transformed into a public Golf course. It has three 18 holes courses and are always fully booked especially week ends and holidays proving that golf is a very popular game in Hong Kong.
Southern half of the island remains wild with large areas of shrub bushes and ravines. Still very much a preserve natural haven for birds and insects.
Once this big island was used by the British Army as a firing range which was harmful to the local fisherman. Luckily there was a lady professor came and live in the village for the research of local culture. She then wrote to the British government and help moving the firing range to Basalt Island instead of here. She also help local fisherman in calling helicopter help when some people got very sick. So after she died, local fisherman erected a memorial plaque in front of the Hung Shing Temple to remember her.
Jin Island (Tiu Chung Chau 吊鐘洲) Jin Island is located more or less at the edge of the inshore islands where the strong ocean wave will be getting weaker as it moves further inshore, hence, no enormous sea arch could be developed before Jin Island. Jin Island is neighbouring to Kau Sai Chau and separated by an extremely narrow channel. The highest point on this island is 216 meters high.
Since the Southern tip of the island is affecting strongly by the Easterly wind, the wave erosion has created one of four famous sea arched here called Tiu Chung Cave(it is actually an arch)(吊鐘洞). We will stop in front of the sea arch for picture taking and appreciation of the natural beauty.
Jin Island is closer toward the centre of ancient volcano, here the volcanic materials forms columns, but in irregular polygonal shape.
Page 25 serious abrasion landforms are almost every where. The famous Sha Tong Hau Cave (沙塘口洞) is located at the headland stretches out to the South. Besides watching at the sea arch, you can see those hexagonal columns on top and by the side of this sea arch happen to be those longest ones around this area. What a grand sight !!!
Ung Kung Group, High Island and Ninepin are situated at the centre of the ancient volcano, columns are in nice shape, some in perfect hexagonal columns.
Basalt Island (火石洲) Basalt Island happens to sit outer most among the Ung Kong Group facing the open ocean directly without any land barrier. It suffers the most from the natural wave abrasion, making it most scenic and dramatic among all islands in Sai Kung. The entire island is extremely rugged with numerous sea caves and plunging cliffs. The famous Lam Wan Kok Cave (欖灣角洞) is found here at the Eastern corner of the island. This is most challenging to adventure seekers as going through the arch could be risky due to the strong wave.
Basalt Island was also once a Firing Range for the British Army until 1985. There were fishermen risking their lives during those days to pick up bomb shells for the metal in exchange for money when they sell it. Unfortunately, sometimes there were bombs unexploded but happened to go off when they picked it up. Some casualties were recorded.
Basalt Island was also the first Air-crash site in Hong Kong. In 1948, a small jet came from Shanghai with an important entrepreneur Mr Yung and the grandson of the American President Mr. Quentin Roosevelt, because of heavy fog, the plane was crashed on this island causing a death toll of 28 people. A small monument was still erected on the island to commemorate the incident.
The name of basalt island tells the uniqueness of the column found in Hong Kong. As most of columns found all over the world are developed in basaltic lava, geologists who have firstly discovered the columns in Sai Kung area also believe the columns are basaltic in nature, so gave a such name ‘basalt island’. The recent scientific research found those columns are rare which is rhyolitic, that is in opposite to basalt in both colour and chemical composition.
Wang Chau (橫洲) Wang Chau is the smallest among the Ung Kong Group. However, the sea arch (橫洲角洞) is the biggest of all the four with 50 meters in height. The shape of the sea arch is also unique from the others as it is narrow at both ends at top and bottom of the arch, but bigger in the center, making it look like a crest of the new moon. From certain angle, it also appears like the shape of Taiwan Island on the map. So somebody also call it the “Little Taiwan”. The island is located at the outer most of on the Eastern end also facing the open sea. Hence, ocean wave effect on this island is very similar to the Basalt Island.
East Dam of High Island Reservoir (萬宜水庫東壩) The High Island East Dam itself is a contemporary man made wonder. From the water side, you can see the construction of the Coffer Dam in details. Just imagine how challenging will it be if we are talking about making, lifting, moving and dropping it to the right position with 7000 pieces of these “Twisted H” shape Dolosse rocks. All these concrete dolosse were made at site here to save the transportation work. Each of these rocks is weighted 25 tons. The twisted arms of the letter H would strengthen themselves by interlocking each other to stand against the roaring waves from the West Pacific Ocean especially during typhoon seasons. In between the arms of the dolosse rock, you could find ample of cavity which will also effectively reduce the strength of waves. What an amazing Italian engineering!!!
The grand construction cover with debris of the tuff rock is the East Dam. In order to increase the water volume, the Dams of this High Island Reservoir are raised to the height of 100 meters.
Hence this reservoir is now largest in volume among the 17 reservoirs in Hong Kong. The discovery of these world’s largest hexagonal rock columns was actually attributed to the construction of this High Island Reservoir. You can see at the far right side several walls are artificially cut out by dynamite blasting. No matter how deep the wall was cut, the rock nature are presenting same type of appearance – walls of columnar joints. Hence the nature wonder was uncovered and after proper management plans were applied in place and we are now proud to say that Hong Kong Geopark is now a global level geopark accredited by the UNESCO.
Please observe the following code and safety guidelines when visiting the geosites in Hong Kong:
1. Never go on a rock or landform appreciation trip alone.
2. Never go on a rock or landform appreciation trip in adverse weather.
3. Plan a safe trip with reference to the tidal information posted on the Hong Kong Observatory's website. Be aware that some coastal areas may not be accessible at all times.
4. Plan a route with a proper trail that ALL members of your group may reasonably handle.
5. Some islands and coastal areas may be difficult to access and are only suitable for boat trips. Avoid visiting them when strong easterly winds prevail.
6. Remain alert to changes in the surrounding environment and any potential hazards, such as rapids, cliffs and steep slopes. Exercise extra caution when rock surfaces are wet.
7. Do not climb the rock columns or trample on severely weathered or eroded surfaces.
Watch out for shifting or slippery rocks.
8. Wear suitable hiking shoes, hats and clothes. Also take gloves, first-aid kits and weather-proof clothes with you.
9. Mobile phone coverage may vary from place to place. Leave details of your route and expected return time with someone, for raising the alarm if necessary.
10. Use only tour guides who have outdoor training and first-aid skills.
11. Use only boat operators who comply with all the safety requirements and have life jackets for all passengers.
12. Do not take away any rock, fossil, mineral or silt. It is an offence to dig up, damage or deface any rocks in Hong Kong.
The conservation of the geo-sites in Hong Kong is in our hands!