Magnificent sea stacks of Ung Kong Group–Bluff Island (Sha Tong Hau Shan)

Magnificent sea stacks of Ung Kong Group–Bluff Island (Sha Tong Hau Shan)

Background Information

Bluff Island (Sha Tong Hau Shan), or Ung Kong Chau, lies west of Basalt Island and south of Town Island (Fo Tau Fan Chau). In the southern corner of this small island you can find one of the four biggest sea caves in our eastern waters ¾ Sha Tong Hau Cave. Viewed from above, Bluff Island resembles a turtle with four legs stretched out wide. Lushly wooded slopes of the rounded hills roll gently down to scenic sandy bays. This is an ideal place to study rhyolite. Formations in clearly defined layers are prominent across the island, and along the wavy shores, huge blocks tower by the water. Fan Tap Pai in the south is one of the most breathtaking coastal rock scenes in Hong Kong. This huge sea cave cuts right through the island and it is just wide enough for a boat to sail past. Not a bad idea for a leisure sea expedition. Bluff Island is also a diving hot spot. An increasing number of divers are coming here to explore the mysterious ocean.

Geological Information

Most parts of the exposed stratum of Bluff Island belong to the Early Cretaceous Kau Sai Chau Volcanic Group. From the Late Jurassic to the Early Cretaceous, this region was the site of earth shaking changes. It began about 146 million years ago (Late Jurassic) when there were violent magma activities. Fiery underground magma intruded upwards, melting ancient rocks along its path. It forced its way through cracks and thrust along crustal faults or weak bands until it reached the surface to cause great volcanic eruptions. Sometimes magma was pressed inside underground voids. It created such an immense force that when it finally broke out it made catastrophic impact. Explosion shot volcanic ash and gravels high into the air. Lava was vented out from the crater from where it coursed down the slopes, igniting fires and generating great clouds of ash and fume. According to data for determining the absolute age of rocks, volcanic eruptions and magma intrusion activities took a cyclical pulse pattern. In every cycle, major eruptions were always followed by great magma intrusions. Such cyclical volcanic magma activities can be categorised into four stages, and consequently there are four volcanic rock groups in Hong Kong ranging from old to new : Tsuen Wan Group, Lantau Group, Repulse Bay Group and Kau Sai Chau Group. Judging by the exposed stratum of Bluff Island, we know that eruptions took place in the 4th stage.

Stunning tubular rock columns and sea caves － Wang Chau

Stunning tubular rock columns and sea caves － Wang Chau

Background Information

Wang Chau is the smallest amongst the Ung Kong Islands. The highest point is merely 80 metres above sea level while the narrowest part measures only 500 metres. It is a barren island with poor soil and hardly any vegetation. Geological sceneries, however, are enthralling. On the north side of Wang Chau one finds a striking sea cave. To see it in true grandeur, visit a few days after a typhoon when the ravaging ocean surge has subsided but the sea is still a little rough. On such days, swirling swells beat up a spectacular resonance in the cave, testifying to the mighty power of nature. Sea cave generally means a pit or trough carved out by waves and currents at the foot of a sea cliff. It is a type of wave-cut landform. Wave-cut action is the damaging impact, erosion and abrasion effect on a coast caused by waves and the sand, gravels and small stones they carry. This process occurs in three forms: erosion, abrasion and dissolution. Erosion is the washing impact of waves and currents on a coast. When waves hit against the rock surface, air in the bedrock cracks is compressed and imposes great pressure on the rock. When the swell subside, compressed air expands suddenly. This continuous process of abrupt contraction and expansion made the rock disintegrate. Abrasion is the impact, chiseling and grinding effect on the bedrock made by sea surge laden with lithic shards and sandy gravels. It accelerates the wave-cutting action. Dissolution means that rock is dissolved by seawater. While carbonate rocks are most vulnerable to dissolution, other rock minerals like orthoclase and amphibolite dissolve more than ten times quicker in seawater than in freshwater. Sea caves, sea cliffs, sea arches, sea stacks, wave-cut platforms and sea terraces are typical wave-cut landforms.

Geological Information

Like Bluff Island, the outcropped stratum of Wang Chau is part of the Early Cretaceous Kau Sai Chau Volcanic Group. Sea caves on the island are well developed. As a result of geological factors and sea level movements, they are greater in depth than width. Major geological factors include the types of shore-forming rocks or substances and their resistance to erosion, attitude of rock beddings, geological composition and crustal movement of the coastal region. These factors influence coastal characteristics and evolution to a great extent.

Typical coastal terrain–Basalt Island

Typical coastal terrain–Basalt Island

Background Information

Basalt Island is an island south of Town Island (Fo Tau Fan Chau) and Wang Chau, east of Bluff Island (Sha Tong Hau Shan) and north of the Ninepins. Only 174 metres at its highest point, it was the site of an air disaster in 1948. An aircraft coming into Hong Kong from Shanghai crashed on the island, killing all 30 crew members and passengers. Sixty years have since passed and all traces have been erased by swells and typhoons. Only an air disaster monument remains on the island to recall this tragic accident.

Geological Information

Like Bluff Island and Wan Chau, the outcropped stratum of Basalt Island is part of the Early Cretaceous Kau Sai Chau Volcanic Group. The island has very well developed sea stacks, island reefs and wave-cut bays which clearly demonstrate the impacts of wave erosion on the environs. Waves, in forms of erosion, abrasion and dissolution, cause devastating damage to the shores. Given that the Kau Sai Chau Volcanic Group is full of columnar joints and fissures, impacts of pounding waves on rocks are particularly obvious. Meanwhile, continuous abrasion by sand and gravel carried by waves has brought changes to the shores and submerged bedrock, sculpting an amazing array of precipitous cliffs and spectacular landforms. In geology, wave cut action is one example of exogenous effect. The islands and wave-cut terrains in the Basalt Island region are excellent showcases that reveal how of this geological process modified geomorphology.

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.

Oldest rock in Hong Kong － Wong Chuk Kok Tsui

Oldest rock in Hong Kong － Wong Chuk Kok Tsui

Background Information

The oldest stratum in Hong Kong, as proven by existing fossil evidence, is a bed of Devonian sedimentary rock. It is mainly outcropped on both sides of Tolo Channel. Sedimentary pyroclastic rocks found around Pak Sha Tau and Wong Chuk Kok Tsui on the northern shore are called Wong Chuk Kok Tsui Formation. They are primarily sandstone, pebbly sandstone and conglomerate. The best outcropped areas of this formation can be found around Wong Chuk Kok Tsui at the northern tip of the channel. Influenced by the folding and staggering action of geological movements, the beddings are almost vertical. It is a breathtaking sight. The rich Devonian fossils found in Tolo Channel provide a strong basis for determining geological age and sequence stratigraphy. They also help us understand how Hong Kong's natural environment evolved during that time.

Geological Information

The oldest rocks of Hong Kong (Devonian) are distributed on both sides of Tolo Channel, i.e. Ma On Shan on the southern shore and the region south of Plover Cove Reservoir on the northern shore. The latter are known as Wong Chuk Kok Tsui Formation. The faults of this formation, some 800 metres thick, have contacts with other strata both in the north and south. The entire Wong Chuk Kok Tsui Formation is made up of clastic sedimentary rocks like sandstone, siltstone and conglomerate. While rock property variations are insignificant from bottom to surface, ages of fossils within cover the entire Devonian sedimentary sequence, from its early stage to the late stage. By analysing the sedimentation and living organisms of the Devonian in depth, we can see that the region around Plover Cove Reservoir on the northern shore of Tolo Channel today was primarily foreshore, river delta or inshore sedimentary shallow sea during the Early and Middle Devonian. Bivalvia, archaeostraca and conchostracan fossils have thus been discovered in this area. Fossils from the Late Devonian are mainly terrestrial primitive ferns. This indicates the sedimentary environment changed at this stage. The sea receded and land was exposed.

Youngest sedimentary rock in Hong Kong － Tung Ping Chau

Youngest sedimentary rock in Hong Kong － Tung Ping Chau

Background Information

Ping Chau, or Tung Ping Chau to differentiate from Peng Chau, sits in Mirs Bay of the northeastern waters. It is the easternmost outlying island of Hong Kong. This crescent-shaped island, measuring 600 metres long and 200 metres wide, is renowned for strange rock formations. Unlike most other rock types across the territory, the island is made up of sedimentary rock including siltstone, dolomitic siltstone, mudstone and chert. This sedimentary rock strata is known as Ping Chau Formation. Many extremely well preserved fossils have been found within the formation. Fossil studies, investigations of rock properties and regional geophysics, as well as research in climatic changes during ancient times have confirmed that this formation is the product of sedimentation which took place in Early Tertiary. Layer upon layer of rock form a bewildering structure. The strata looks just like a huge book, guarding great mysteries of geological history within its numerous pages. Since no sediments after Early Tertiary have successfully solidified into enduring rock, Ping Chau Formation is the youngest rock in Hong Kong's geological history. Tung Ping Chau is a popular holiday destination. Its many fascinating attractions, such as wave erosion landscape, the shale that resembles a layered sponge cake and the unusually flat lay of the island itself, have drawn thousands of visitors to the island.

「Three Flats and One Wonder」

Three flats are flat sea, flat island and flat rock. Tung Ping Chau is only 1.1 square kilometres in size. An island of extremely low elevations, it really lives up to its name. The highest point in the southeast, Hok Ngam Teng, rises a mere 48 metres above sea level, while the highest peak in the northwest, Au Kung Shan, is only 37 metres. As for the wonder, it refers to the famous shale.

「Top Rock」 The Tung Ping Chau shale is rated as the No. 1 rock in Hong Kong for the following reasons : Clearly defined bedding and distinctive sheet conformation This is the most significant characteristic of shale. Every layer is 1 to 5 mm thick. Overlapping each other, the coarser-grained siltstone layers and the finer-grained mudstone layers have clear lamination and sophisticated structure. These shale beds are believed to date from Late Cretaceous to Early Tertiary. It is a safe guess that Mirs Bay and Tung Ping Chau were a remote salt lake detached from land. As a result of sedimentation over long ages, shale resembling a layered sponge cake emerged in the hypoxic, highly salt and still water. Attractive and colourful Shale is usually made up of pyrite, geolite and augite. The vivid colours come from micrograined calcium, iron and magnesium particles that the rock contains. After formation, the rock was exposed to weathering and wave action, creating eye-dazzling plum, ochre, charcoal and bottle-green outcrops. Vague ripple marks Close observation will reveal vague or faint ripple marks in every layer. We can thus infer that the rock was close to the lake surface or submerged in relatively shallow water at the time of formation. In such setting, even small ripples would leave detectable marks. Emulsion and regeneration of vertical lamination At Chau Mei Kok, you can find vertically fused or dotted reticulation on the shale sections caused by emulsion. As shale has high calcium content, when it is subjected to tidal, wave and sea current erosion, as well as impacts of salinization, wind, sun and rain, it develops melted calcium sections similar to stalactites. Later when the melted calcium is released, it flows out vertically at the outcrop tips or agglomerates into visible dotted reticulation. This is called vertical emulsion.

Internationally rare acidic polygonal volcanic rock columns － High Island

Internationally rare acidic polygonal volcanic rock columns － High Island

Background Information

High Island Reservoir is one of Hong Kong's most popular geological sites, and home to our most spectacular rock wonder. Here, volcanic rock composes neat arrays of giant polygonal joint columns along the shore. Amongst these the hexagonal rock columns are most typical examples. Catching your eyes with striking angular facets, these giants are rare natural prodigies and invaluable geo-tourism resources that draw great interest. Around High Island Reservoir, especially the East Dam, you can observe the most typical hexagonal columnar joints from different angles. There is also a chance to examine the rock composition and structure at close range. Looking down from the East Dam rock cliff, you have a clear view of buckles in the hexagonal columnar joints. Judging by the s-shape section, we know the rock columns buckled under gravity before it could cool down completely and solidify, and thus the scene we see today. With such evidence, it is easy to trace the formation of volcanic extrusive rock. At the observation point for the hexagonal columnar joints, you can also find outcropped basic lamprophyre veins. Lamprophyre is a dark dyke comprising mainly biotite, amphibolite, augite and light minerals like plagioclase and orthoclase. It is usually in vein attitude and wide distribution. Po Pin Chau just off the East Dam is another interesting place to see extraordinary formations. This is where you find giant stacks that emerged when a complete hill was slashed into two by natural forces. It is undoubtedly a fine example amongst similar geo attractions. Geology enthusiasts will certainly cherish the opportunity to see towering rock stacks and fascinating hexagonal joints. Maritime explorers will find Po Pin Chau intriguing and unforgettable. After admiring nature's exquisite works, don't forget to see High Island Reservoir, the impressive man-made wonder. This water storage facility is the biggest in Hong Kong. It is also a water project of key importance. The dramatic East Dam and West Dam are great attractions in their own right. The seafront is protected by concrete dolosse units. Functional as it is visually appealing, this cofferdam attracts many visitors.

Permian rock garden of Hong Kong － Ma Shi Chau

Permian rock garden of Hong Kong － Ma Shi Chau
Background Information
The Tolo Channel Geo-Area includes the north shore of Tolo Channel, Ma Shi Chau on the southwest shore and Lai Chi Chong on the south shore. Most of the rocks along the north shore of Tolo Channel and at Bluff Head are the oldest in Hong Kong, formed about 400 million years ago during the Devonian Period. Ma Shi Chau presents the sedimentary rocks formed about 280 million years ago; the rocks are the second oldest rocks in the rock region; Lai Chi Chong showcases various volcanic rocks and sedimentary rocks formed about 146 million years ago. These two geo-sites also show distinctive geological features, such as faults and folds. Although the geology of Ma Shi Chau and Lai Chi Chong is a bit complicated, they are the ideal destinations for geologists. The 61-hectare Ma Shi Chau is made up of Ma Shi Chau, Yeung Chau, Centre Island and an unnamed islet to the northeast of Sam Mun Tsai New Village. Ma Shi Chau is the key site of Hong Kong's Permian Tolo Harbour Formation. Home to well-outcropped rocks, the island is an ideal location for studying strata, rock properties, sedimentation features and different geological compositions because here you can find faults and folds as well as deformed and displaced rock mass. The unnamed islet near Yim Tin Tsai, vegetated with dense woodlands, is a popular roosting ground for egrets and herons. Given such outstanding conservation value, the Ma Shi Chau region was declared a protected Special Area in 1999. The Ma Shi Chau nature trail runs along the southeastern shore of the island. 1.5 km in length, this route presents 16 attractions which highlight local geological features. By observing the rocks on site and reading trailside interpretation plates, visitors can understand how tombolos and various rocks are formed, as well as natural phenomena like wave erosion, weathering and folding .
Geological Information
	Outcropped strata dating back to the Permian (290,000,000 to 250,000,000 years ago) are extremely rare and isolated in Hong Kong. Tolo Harbour Formation is a particularly prominent example. This formation is mainly distributed across Tolo Harbour and its environs, such as Ma Shi Chau, Centre Island, the Chinese University of Hong Kong and the western shore of Three Fathoms Cove. Ma Shi Chau is a representative showcase of this formation. The well-outcropped rocks on the island are composed of mudstone, siltstone and sandstone deformed by folding . Centre Island to its south is made up of the same rocks. The sandstone there exhibit ripple marks corrugated and flaser-bedding, while the siltstone often manifests bioturbation. Extensive Permian sedimentary rock layers are not the only geological attraction of Ma Shi Chau. Here on the island, you can also find faults and folds, deformations and displacements. On the northwestern edge, some outcrops are part of the Early Jurassic Tolo Channel Formation. These include dark siltstone, mudstone and Late Jurassic sedimentary breccia, tuff and tuffite. The Permian rock at Ma Shi Chau is estimated to be approximately 500 metres thick. It has two lithofacies. The lower facies in the southeastern part of the island is an assembly of powdery grey to pale red calcareous siltstone and charcoal-tone alternation beds of mudstone, siltstone and sandstone. The sand content increases upwards progressively and transits to the approximately 0.5m thick sandstone beds. The upper facies in the northern part of the island is mainly thick layers of siltstone, sandstone and conglomerate. Depositional environment is stable and each layer is as thick as 1 metre. Fossils like mollusks, corals, bryozoans, brachiopodas and crinoids have been discovered both in the upper and lower facies. Judging from the rock facies and their features, as well as the presence of both marine fauna  fossils and terrestrial flora fossils, we can make a conjecture that the Permian rocks in Tolo Harbour and nearby regions were formed in a shallow estuary. The well developed stratification, alternate sandstone and siltstone beddings, as well as cross bedding or  flaser-bedding, are evidences of frequent changes in sediment sources and hydrodynamic conditions. All these are characteristics of a shallow estuary environment.

Memories of volcanic lava flows － Sharp Island (Kiu Tsui Chau)

Memories of volcanic lava flows － Sharp Island (Kiu Tsui Chau)
Background Information
Sharp Island (Kiu Tsui Chau) is just 2,000 metres off Sai Kung Pier. Set in Port Shelter, it lies southeast of Sai Kung town centre and east of Kau Sai Chau which is about 1 km away. This south-north trending island is long and narrow, extending some 2,500 metres long and about 500 metres wide from east to west. The highest point is 136 metres above sea level. Kiu Tsui Country Park is the smallest of its kind in Hong Kong. Covering only 100 hectares of island territories, its boundaries take in several islets, including Cham Pin Chau, Pak Sha Chau, Tai Tsan Chau, Cham Tau Chau and Kiu Tau. This popular holiday destination offers lucid water, silvery sand and dreamy vistas of island reefs and pristine woodlands. Visitors can explore the main island along a pleasant hiking trail, or walk across a spectacular natural sand levee that connects Sharp Island with neighbouring Kiu Tau. A sand levee is a coastal sedimentary landform. In geology, it is known as a tombolo. The Sharp Island tombolo is about 250 metres in length. It is flanked on both watersides by medium to fine grain sand and seashell debris, while the centre is coarse sand mixed with gravel. This natural tombolo is one of several tombolos found in Hong Kong. Similar terrain features can be seen in Pui O of Lantau and between Ma Shi Chau and Yim Tin Tsai. The Sharp Island tombolo is not always visible. Emerging only when low tide , it is a popular place for a seaside stroll or a dip in the sea.
Sharp Island is an iconic example of wave erosion landscape. Relentless erosive action has sculpted an eclectic array of bays and headlands : Hoi Sing Wan, Ha Mun Bay, Long Mong Wan, Shek Kwu Wan. Among them Kiu Tsui Beach and Ha Mun Bay are the best beaches. The former, situated near Sharp Island on the western shore of the island, is a favourite destination for seaside recreation. There are lifeguards on duty to ensure safety and visitor facilities include changing rooms, showers and a beachside barbecue area. The latter, situated in southern Sharp Island, is a crescent-shaped beach. Also known as Half Moon Bay, it is an excellent beach backing on to expansive grassland. Facilities include a barbecue area and campsite, changing rooms, showers and kiosk. It is one of the hottest swimming and barbecue destinations of the Sai Kung islands.
Tombolo is accessible when tidal level is lower than 1.4 meter. Visitors should note the tidal levels before crossing the tombolo. Please refer toHong Kong Observatory for tidal information.
Geological Information
	Most outcropped strata of Sharp Island belong to Mesozoic Cretaceous volcanic Clearwater Bay Formation, a formation composed primarily of flow-banded porphyritic rhyolite lava,  rhyolite breccia and eutaxitic vitric tuff. Clearwater Bay Formation is part of the Kau Sai Chau Volcanic Group, the youngest of its kind in the territory. It is marked by features of volcanic activities in Hong Kong during the final stage of the Mesozoic Era. Also found on Sharp Island, just below Clearwater Bay Formation, are Mang Kung Uk Formation volcanic rocks. The rock here is essentially tuffaceous siltstone mixed with crystal bearing fine ash vitric tuff and tuff breccia. All the above are extrusive volcanic rocks. Rhyolite is an acidic extrusive rock formed by solidification of cooled granitic magma extruded upon the ground surface. It is so named for the iconic flowing lines. Observed under a microscope, you can often find rhyolitic and porphyritic vitreous properties, pellets, felstone and micrographic textures. Phenocrysts are usually quartz and alkali feldspar, and occasionally containing a little plagioclase. The groundmass is usually tight cryptocrystalline or vitreous substances. In most cases, distribution of  rhyolite formed by lava flow is limited, as this type of rock is usually outpoured by relatively small volcanic domes and lava flows. Hong Kong is no exception. Apart from Sharp Island, similar flow-banded lava can only be found in Yim Tin Tsai. The rhyolite lava of Sharp Island is living record of ancient volcanic eruptions and lava flows. While characterised by flow lines, it is also highly porphyritic. The phenocrysts are mainly quartz and sanidine, with the occasional presence of plagioclase in varied concentrations. This rhyolitic and porphyritic structure is very often the product of devitrification. Rhyolitic lava is widely distributed in southeast coastal provinces of China, including Liaoning, Inner Mongolia, Hebei, Shanxi, Shandong, Jilin and Heilongjiang. Significant distributions of current acidic volcanic rocks are generally made of welded tuff. This rock is outpoured by sheets, volcanic domes and dykes. In Hong Kong, most outcropped volcanic rocks are such tuff emerging in island arcs and active margins or created by continental intraplate activities. The tectonic setting of Hong Kong lies within a continental margin. In the Late Jurassic and Early Cretaceous massive volcanic eruptions took place. Most volcanic rocks seen today were formed during such times. At the northern tip and west side of Sharp Island, you can find porphyritic fine to medium grained quartz monzonite. This is an acidic intrusive rock whose chemical composition is between granite and granodiorite. Granite and granodiorite are both acidic rocks with abundant quartz and feldspar substances. Major differences being that granodiorite is slightly less acidic than granite; granite contains more potash feldspar than plagioclase; and granodiorite contains more plagioclase (acidic plagioclase) than potash feldspar. When the plagioclase and potash feldspar contents are level, it is known as quartz monzonite. Given that the Sharp Island rock mass has the same property as the quartz monzonite in Tai Mong Tsai, Sai Kung, it is known as the Tai Mong Tsai Quartz Monzonite.

Danxia wonder at sea － Port Island (Chek Chau)

Danxia wonder at sea － Port Island (Chek Chau)
Background Information
Sitting at the mouth of Tolo Harbour in Tai Po, Port Island overlooks the southern Tap Mun Island. This uninhabited island may seem lone and barren, but it is the gateway of Tolo Harbour for it guards the strategic pass of Tolo Channel. As the Chinese name Chek Chau implies, Port Island is a place of red earth. The ground on the entire island is rust-coloured conglomerate and siltstone. From Wong Chuk Kok Hoi to Hung Shek Mun, past Tsat Shue Wan, Cheung Tsui to Hung Pai, it is a grandiose domain of red peaks, rusty soil, red earth and green trees. This extraordinary scene is known as “Danxia Wonder at Sea”.
Red earth landscapes are called “Danxia” wonders in China. Examples are Danxia Shan in Guangdong, Wuyi Shan in Fujian and Lungfu Shan in Jiangxi. Port Island is the number one representative of Hong Kong. Other danxia sites are Kung Chau, Ap Chau and the Hong Kong Red Sea. Dazzling red terrain is the biggest fascination of Port Island. The hills are completely covered with reddish-brown conglomerate and siltstone, making it a true “red island”. What brought about such unusual sights? Geologically, the answer lies in the ancient times. After more than 6 million years of robust lava and volcanic activities, most regions of Hong Kong became igneous rock terrains. When volcanic activities subsided, extended dry climate set in. Great temperature difference between day and night caused avalanches. Weathered rocks toppled down from the uplands and were quickly transported and deposited. Gravel, sand and silt arising from weathering were washed down by seasonal rainstorms to the alluvial plains where they settled. There, the ferric minerals within turned into iron oxide and bonded sand and other sediments to become a unique red sedimentary rock. Hot climate and the scorching sun aided release of iron in the sand and gravel. For this reason they were tinted red or rust in various intensities. Sediments of the alluvial plains and river channels eventually formed the red or coloured terrestrial clastic sedimentary rocks seen on Port Island today. Main components are conglomerate, sandstone and siltstone. These rocks are known as Port Island Formation.

Volcaniclastic sedimentary rock － Lai Chi Chong

Volcaniclastic sedimentary rock － Lai Chi Chong

Background Information

On the southeastern shore of Tolo Channel in the Eastern New Territories, a set of Early Cretaceous volcaniclastic sedimentary rock strata called Lai Chi Chong Formation are distributed around rural Lai Chi Chong and nearby coastal areas. They are “younger” than the sedimentary rock of Ma Shi Chau but “older” than that of Tung Ping Chau. Research has shown that this region has rather complicated geological setting and rock types, with Mesozoic volcaniclastic sedimentary rocks, tuff, rhyolite and Paleozoic sedimentary rocks occurring locally. The uneven stratum on the foreshore near the Lai Chi Chong pier is volcanic ash sedimentary rock. Displaying very distinctive foldings, faults and bedding structure, it is an ideal location for geological study.

Geological Information

Major outcropped sections of Lai Chi Chong Formation can be found on the beach west of Lai Chi Chong pier. Although less than 200m wide, these sections manifest extremely complicated rock properties that include tuffite ,tuffaceous sandstone, siltstone, coarse ash crystal tuff, eutaxitic fine ash tuff and porphyritic rhyolite in current bedding. Bedding development is excellent with a wealth of visible sedimentary structures, such as current bedding, graded bedding, convolute bedding and subaquatic slump. Signs occurring from folding, fault and discordance of strike directions are also clearly noticeable.

Double Haven (Yan Chau Tong)

Serene and picturesque marine park － Double Haven (Yan Chau Tong)

Background Information

Double Haven (Yan Chau Tong) rests on the northeastern shore of Plover Cove Country Park. The Chinese name Yan Chau Tong is probably inspired by an interesting looking islet which takes the shape of a stone seal. To conserve the wildlife and natural features of this lovely area, Double Haven was designated a marine park in 1996. Double Haven is a idyllic arcadia embraced by uplands. It owes its celestial tranquil setting to the surrounding hills. Well shielded on four sides from the open sea, it is relatively unaffected by the southeast summer monsoon and northwest winter monsoon. The air is a little dryer than other parts of Hong Kong and there is seldom heavy rain. Although a whole network of small streams flow into Double Haven, they never cause any widespread flooding. Bestowed with such supreme qualities, it is no surprise that Double Haven astonishes every first-time visitor with her stunning beauty. That unique serene mood is simply unimaginable in bustling Hong Kong.

Geological Information

The present landscape of Double Haven originates from a series of volcanic eruptions in the Middle Jurassic 180 million years ago. Devastating explosions destroyed the original sedimentary rock which comprised mainly sandstone and siltstone. Great clouds of volcanic ash mixed with lava settled on the ground and formed a volcanic rock stratum about 2,000 metres thick ¾ the coarse ash crystal tuff that extends from the area north of Sam A Wan to Lai Chi Wo and Sha Tau Kok today ¾ and Double Island, Crescent Island and Crooked Island. As eruptions and volcanic activities gradually stopped, this region underwent about 20 million years of erosion and weathering when rivers washed sand and gravels down the surrounding mountain ranges to settle in the downstream coastal flats. They formed the conglomerate, sandstone, siltstone and shale of Double Haven, Pat Sin Leng and Port Island (Chek Chau). The sedimentary rocks in these parts are about 500 metres thick.

Hong Kong Global Geopark

Local Participation As a Global Geoparks Network requirement, Hong Kong Global Geopark welcomes any public or private partnership proposal from the community to support the sustainable development of the geopark. Genuine and sustainable local participation Role of Hong Kong Global Geopark Geopark Principles for partnership recommendations

L’hotel Island South has made a partnership arrangement with Hong Kong Geopark to be the first “Hong Kong Geopark Hotel”.  The Hotel is committed to geoconservation and promotion of geopark concept.  Lobby and selected rooms are decorated with geopark theme.  Geopark videos are broadcasted in the hotel lobby and dedicated in-room TV channel.  Specially designed geopark menu is also available in the hotel to assist the publicity of geoconservation and geopark guided tours. Familiarization field trip Staff training

Friendly geo-facilities and service

TV booth for geotour e-Kiosk In-room TV channel Fossil decoration Geolicious Menu Factsheet Appetizer Dish Name Dish Description Geo Park Feature Picture Geo description Iconic Columnar Rocks Go On-stage Tuna Pyramid with Apricot Sauce Hexagonal Columnar Rock  Spectacular hexagonal columnar rock covers the whole Sai Kung area, they are the products of volcanic activities. The Classic Rock Cascade Italian Copper Ham with Potato Salad & Crispy Onion Bluff Head Bluff Head displays the oldest rock in Hong Kong. The inter-layered red and white rock strata formed about four hundred million years ago. Soup Dish Name Dish Description Geo Park Feature Picture Geo description The Cracked Dome Oven-baked Pumpkin Potage with Puff Pastry Sharp Island Continuous sun and rain lead to the exterior of boulders on sharp Island splitting into pieces, which look like a huge pineapple bun. Caution! The Bubbling Lava! Breaded Soup Beef Goulash Bluff Head Crater collapsed when it lost support and formed a large bowl -shaped Caldera. Main Course Dish Name Dish Description Geo Park Feature Picture Geo description Duck’s Eye over the Water Crispy Prawn Wrapped with Kataifi & Fresh Mango Sake Kasu Ap Chau Bedrock  The well-known Duck’s eye is a typical sea arch, it is formed by continued coastal erosion. Challenge the “Jenga” Rocks Oven-baked Australia Miso Cod Fillet with Leek & Matsutake Sedimentary Rock Sedimentary rock is layered rock which is formed by compaction of sediments accumulated in water layer by layer. Geo Trio Charcoal Grilled U.S. Short Rib with Egg-plant Gratin The Ninepin Group The Ninepin Group mainly consists of South, North and East Ninepin Islands. Huge hexagonal rock columns are widely distributed on the islands.   The Muddy Sandstone Crossover  Slow Cooked U.S. Beef Tenderloin with Green Tea Sea Salt Flakes Siltstone Siltstone is a kind of sedimentary rock which is formed by fine rock fragments, the texture is in between of mud and sand. Cake Series Dish Name Dish Description Geo Park Feature Picture Geo description Placoderm the Crispee Vanilla Ice Cream with Crispy Chocolate Placoderm Placoderm is an extinct fish. Its head to thorax were covered by armoured plates. Rock the Rockies Crispy Chocolate Parfait with Mocca Profiteroles Wang Chau Under the erosive power of waves, diverse coastal landforms are well developed along the Sai Kung coast, such as sea cliff and sea cave The Chocodeck Chocolate Mousse Mille Feuille Tung Ping Chau Tung Ping Chau is made up entirely of layered sedimentary rock, which is the youngest rock of Hong Kong with a history of about 55 million years. The Sleeping Beauty Chocolate Chiffron Dome  Volcano Around 160 million years ago, Hong Kong was in the period of volcanic activities, a series of violent volcanic eruption had occurred in Hong Kong. Requirements for organizations seeking a partnership arrangement with Hong Kong Global Geopark of China Be committed to geoconservation and the promotion of Hong Kong Global Geopark. Facilitate the promotion and operation of geopark tours led by Recommended Geopark Guides (R2G)s. Display or exhibit at prominent places in the venue(s) of the programme science popularisation and Hong Kong Global Geopark messages following the geopark communication concepts. Provide products which will help promote geopark branding. Ensure staff members in charge of the programme undertake geopark familiarization training. Designate staff member(s) of managerial grade to address to the geopark-related enquiries. Undertake to work closely with Hong Kong Global Geopark with a view to achieving the key objectives set by the Global Geoparks Network. A partner meeting the above requirements may use the Hong Kong Global Geopark logo as confined to geopark related products or activities agreed by Hong Kong Global Geopark. Either party may terminate this arrangement without advance notice by giving notice to the other in writing.