Spectacular joint columns–Ninepin Group (Kwo Chau Islands)

Spectacular joint columns–Ninepin Group (Kwo Chau Islands)

Background Information

Located about 15 km southeast of Sai Kung Town Centre, the Ninepin Group comprises South Ninepin Island, North Ninepin Island and East Ninepin Island, along with several small rock islets. It is located in the open sea and is thus subject to the relentless impact of strong wind and waves, resulting in diverse peculiar coastal landforms, including steep cliffs, sea arches and various strangely-shaped rocks. Famous scenic wonders on North Ninepin Island include Cannon Rock, Moon Rocks and Big Stove Arch; and on South Ninepin Island include Stone Arch, Jacob's Ladder Cave, Backwash Cave and Y-shaped Cave. In the Sai Kung Volcanic Rock Region, the hexagonal rock columns exposed on North Ninepin are the most magnificent. The columns may have a diameter of over 2 m, making them the largest in the area. As the Ninepin Group is within the core protection area, and in view of the strong wind, big waves and dangerous terrain, sightseeing is suitable only on calm summer days, and only boat tours with no land excursion. The name "Ninepin" is inspired by an old British game similar to modern day bowling. When British seamen first saw the array of these islands, the familiar bowling game sprang to mind and they gave the group this colourful name. The Chinese name Guo Chau, meaning fruit island, is even more innovative. It is said that the Ninepin Group (Kwo Chau Islands) was originally called Guo Pun Chau which means fruit platter. It is so named because viewed from above, the group looks like scattered fruit from an overturned platter from heaven. The Ninepin Group is made up of North Ninepin Island, South Ninepin Island, East Ninepin Island and other islets. North Ninepin includes Sai Mei Chau and Hok Tsai Pai. South Ninepin includes Tai Chau, Tai Chau Mei, Ta Long Pai and Lai Chi Pai. East Ninepin includes Tuen Chau Mei, Shue Long Chau and Lung Shuen Pai. Riding on a small boat to South Ninepin Island, the sea is calm and beryl. After going ashore, the first thing that comes to view is the imposing "Tiger Mouth Cave". Hong Kong's eastern coast has its fair share of famous caves, and this is one of them. In geology, this "cave" is actually a sea arch. Hong Kong is influenced by easterly wind most part of the year. The islands east of Sai Kung and Clearwater Bay peninsula are completely exposed to this natural force. Even though volcanic rocks are essentially hard and resistant, wind and waves have taken their toll over the ages. The resultant terrain is rugged and imposing. Given such challenging condition, visitors to the Ninepins can only get ashore during two or three summer months every year. Standing below the giant arch, one will marvel at nature's brilliant craftsmanship and truly appreciate the greatness of nature's power relative to our own.

A rugged and barren hill path leads to Nam Yue Tau, passing through many natural rock arches that may suddenly collapse any day. Looking east, the seascape is boundless. With the nearest land being the Philippines, no wonder fishermen built a Hin Hau Temple here on this last outpost. Along the way, the soil is barely covered except for some grasses, shrubs and coastal plants. Beach Naupaka (Scaevola taccada) and Screw Pine (Pandanus tectorius) are two key species. The rocks here are marked by interesting graphics. At first glance, you may think that some idle impressionist or post-modernist painter has dressed them up with his works. They are in fact mother nature's masterpieces. About 160 million years ago, an earth-shaking eruption caused fundamental changes to the nearby coasts. Along with scorching volcanic ash, great acidic lava was spewed out from the volcano, covering slopes and the land. When large areas of volcanic ash and lava slowly cooled down to become solid rock, the contraction effect gave rise to extremely uniform hexagonal cracks and joints. What followed were climatic changes over millions of years. The combined impact of wind, rain and ocean surge brought out various minerals which were once hidden within, decorating the pale rock face with a dash of colour. Sailing from South Ninepin to North Ninepin, the spectacular hexagonal volcanic rock on the island is visible even from quite a distance. Volcanic rock made up of black basic basalt is not particularly rare yet such large coverage of hexagonal joint volcanic rock formed by cooled and solidified pinkish acidic rhyolitic volcanic rock is very seldom seen. This unique natural wonder features volcanic rock arranged in a striking formation of giant hexagonal columns. An islet off the east shore called Yuen Shek Pai offers the most amazing sight. Numerous rock columns rise up neatly around the centre of the islet and form a natural spiral staircase.

Geological Information   The outcropped volcanic rock with columnar joints of the Ninepins is a type of acidic rhyolite volcanic rock. The rock is relatively consistent and has significant contents of potash feldspar and quartz phenocrysts. This rock set, known as the High Island Formation, is part of the Early Cretaceous Kau Sai Chau Volcanic Group. Rocks of the Ninepins date back to the age of dinosaurs about 140 million years ago. It is believed that this group of islands were created by a major volcanic eruption which produced about 70 cubic kilometres of volcanic ash. A series of peaks emerged abruptly on the broad plain as a result. Given that Mount St. Helens spewed out only 2 cubic kilometres of ash when it exploded while the catastrophic Krakatau eruption of Indonesia in 1883 produced 12 cubic kilometres of volcanic substances, one can imagine the devastating magnitude of this ancient eruption. After rising, these peaks faced severe erosion over millions of years. Gradually they became the magnificent rugged landscape we see today.