1-1. Location

The Penghu Columnar Basalt Nature Reserve is located in the northeast end of Taiwan’s outlying Penghu Islands. The site includes the islets of Xiaobaisha, Jishan, and Dinggou.

1-2. Area of Coverage

• The Penghu Columnar Basalt Nature Reserve is the only nature reserve located on an outlying island of Taiwan.
• The total area of the Reserve is 19.13 hectares at high tide and 30.87 hectares at low tide.
• The buffer zone includes inhabited islands and newly formed sandbars such as Yuanbei Islet (26.53 hectares), Niao Islet (27.76 hectares), Nanmiangua Islet (4.78 hectares), Quzhua Islet (14.19 hectares), Beijiao (1.70 hectares), and Huolong Beach (a newly formed sandbar with unfixed surface area that changes according to sea currents each year), altogether occupying a total of 74.96 hectares.

2-1. Geology of Penghu

The volcanic rocks that make up Penghu Islands are basaltic. The young basalt is black in color, hard in texture, and contains very fine and crystallized mineral content. According to research on the region’s formation, Penghu Islands are layered with flood basalts formed by a series of lava basalt flows.

The uninhabited islets of Dinggou, Jishan, and Xiaobaisha are basalt formations created by a series of underwater volcanic eruptions that occurred more than 10 million years ago. The rapid cooling of lava flows caused significant contraction, leaving behind massive columns with hexagonal or polygonal texture.

The formation of Penghu Islands was a result of rapid cooling of lava flows following volcanic eruptions from the ocean floor. The naturally formed columnar jointed basalt is arranged in various shapes such as sloping cliffs, radiating patterns, and horizontal pillars, creating landscapes that are rarely found elsewhere in the world. 

The alkali basalt in this region contains phenocrysts of olivine and augite, which are yellow or green in color and lend their hues to the landscape.

2-2. Ecology of Penghu

The collective of Penghu Islands is located at the juncture of three critical marine phenomena – the nutrient-packed Kuroshio Current, warm surface currents from the South China Sea, and oscillating tidal streams.Rich marine resources in the surrounding seas attract many migratory birds during wintertime, and the region also serves as a breeding paradise for terns during summertime. Protected and valuable species such as the Roseate Tern, Little Tern, Bridled Tern, and Black-nappen Tern often visit and breed in this area as well. 

In recent years, long-term investigation in Penghu has identified bird sightings from 14 different orders and 40 families, totaling 157 species. Within the Reserve alone, there are a total of 52 species of birds from 10 orders and 19 families. Since the three main islets of the Reserve have neither forests nor lakes for birds to nest, most birds found in this area are migratory birds. The Pacific reef heron and Oriental skylark, however, are yearlong residents.

Summer migratory birds include the Little Tern, Bridled Tern, Black-nappen Tern, Roseate Tern, Great Crested Tern, and Common Noddy; whereas winter migratory birds include the Whimbrel,  Ruddy turnstone, Blue rock thrush, Common sandpiper, and Kentish plover. Among the species that come to nest in Penghu, the Roseate Tern and Peregrine falcon are on Taiwan’s Red List for endangered species. The rest of the birds are either lost or only making a brief stop.

Terrestrial creatures, especially insects of this region, rely on plants for survival. The evolution of vegetation in the Reserve have subsequently led to changes in dependent insect species. The most dominant insects here are locusts such as Patanga succincta Linnaeus, and butterflies such as Zizina otis riukuensis, Nacaduba kurava therasia, and Eurema andersoni godana.

The three islets in the Reserve were originally barren basalt plateaus. After the passage of time eroded a minute amount of basalt, gravel and sand grains slowly accumulated and finally made life possible on the plateaus. The region’s vegetation diversity was further nourished by excrements left by migratory birds, seeds sent by the wind, and an assortment of drift materials carried by the sea.

Nevertheless, only stoloniferous plants – those with creepers running across or below the ground –of short and small stature can survive in the region’s harsh conditions of limited ground area, strong winds, rapid evaporation, and salinized soil. Field investigations show that Xiaobaisha Islet contains 14 orders and 22 species; Jshan Islet houses 10 orders and 13 species; and Dinggou Islet supports 4 orders and 6 species.

There are two endemic plants named after Penghu – the Penghu soybean (Glycine pescadrensis Hayata) and Penghu Water Willow (Justicia procumbens L. var. hayatai Yamamoto). Other rare varieties in this region include the ground-hugging Portulaca insularis Hosokawa and Euphorbia atoto G. Forster, and the white-blossom variety of Ipomoea imperati.

2-3. Stone Weirs of Penghu

Stone fish weirs are one of the most iconic features of Penghu's coral reef fishery. Weirs, or tidal traps, are found in both Taiwan and many other countries, but Penghu has the highest density of such contraptions.

The southwestern to northwestern shores off Xiaobaisha Islet are predominantly shallow waters that are home to a rich ecology of coral reefs, fish, and shellfish species. The shallowness afford easier access for Penghu residents to harvest food from the sea using methods such as fish weirs. As an example of the weir’s importance to the local way of life, a valuable stone weir at the southwestern end of the islet took 18 years to construct.

Today, there are more than 574 weirs of different size and shape scattered across Penghu. Although usage has decreased following the decline of marine resources in recent years, the weirs remain important cultural heritage sites for Penghu’s growing ecotourism.

The diverse landscape of the Penghu Columnar Basalt Nature Reserve is comparable with that of Giant’s Causeway and Causeway Coast in Northern Ireland and Fingal’s Cave in Scotland. The Reserve’s three islets are masterpieces by nature that are unique in design, scale, and craftsmanship. 

3. Geological History of Penghu

According to geological studies, the basalt that formed most of Penghu was the result of cooled lava flows after a series of underwater eruptions, and the oldest basalt identified in the region can be found at Tiantai Mountain on Wangan Islet. The lava started to flow about 18 million years ago and the last eruption occurred at Dongyuping Islet around 8 million years ago.

The geological age of the Reserve can be dated back from 13.2 million years to 11.8 million years ago, giving rise to a wide array of unique columnar basalt across the islets.

Penghu was once known as “Xiying,” “Penghai,” and “Pinghu.” The culture and history behind each name contain historic significance. Early European sailors christened the islands “Pescadores,” meaning “the island of fishermen.”

Penghu was explored by settlers 400 years earlier than Taiwan proper. As early as 1281, Kublai Khan, the Mongol founder of the imperial Yuan dynasty, had established an inspection and patrol outpost on Penghu. Dutch colonists seized control of the islands by 1622, and fixed artillery batteries were constructed to defend against pirate invasions.

In 1624, Dutch colonists were defeated by Qing troops and retreated to Taiwan proper. However, the Qing government had to cede Penghu Islands to Japan following the First Sino-Japanese War. It was not until Japan’s surrender in the World War II did Taiwan acquire sovereignty over Penghu in 1945.

Criterion VII:

The diverse columnar jointed basalt of Penghu Islands were formed by a series of rapidly cooling lava flows from deep sea volcanic explosions. Moreover, the basalt-formed islets gained superlative landscapes such as cliffed coasts, littoral caves and grottos, sea stacks, and groove marks after erosion by the abrasive sea. Such basalt landscapes are rarely found in other Asian archipelagos, meeting UNESCO’s seventh selection criterion on exceptional natural beauty and aesthetic importance.

Criterion VIII:

The basalt of Penghu Islands was formed in an era where volcanos were the most geologically activein the Taiwan Strait. The well-preserved columnar jointed basalt and the diverse landscapes in this region meet the eighth selection criterion on representing major stages of Earth’s history and containing significant geomorphic features.

Criterion X:

Due to its isolated location, torrential currents, and steep cliffs, the Penghu Columnar Basalt Nature Reserve has very few human visitors. Each April through September, the Reserve provides a safe breeding haven for protected and valuable species of birds. Endangered green sea turtles were also spotted laying their eggs in the Reserve during 2002. The region contains significant natural habitats for in-situ conservation of biological diversity, matching the tenth selection criterion.

Penghu Islands are surrounded by turbulent outer seas while its inland seas are as serene as lakes. The archipelago is constructed by flood basalts, encompassing roughly 100 cays scattered within a region measuring 60km on the south-northern stretch and 40km on the west-eastern stretch.

Located by the coordinates 23°N 119°E, Penghu is the only outlying island collective constructed by basalt in Taiwan.

5-1. Geological History of Penghu

According to geological research, the basalt-formed Penghu Islands are the result of a series of underwater volcanic eruptions. Tiantai Mountain on Wangan Islet contains the oldest basalt in the region.

Lava began to flow about 18 million years ago, and after the last eruption at Dongyuping Islet around 8 million years ago, the submarine volcanos have ceased activity. The jointed basalt on Tiantai Mountain is remnant of the oldest basaltic lava known among Taiwanese islets, and Dongyuping Islet was the last Penghu islet to be formed.

5-2. Stratums of Penghu

There are two to three layers of lava on the surface of the archipelago that can be chronologically dated to the middle or late Miocene epoch of the Tertiary Period. Such stratums are most visible and commonly found on Yuweng Islet and are henceforth named after the islet.

The archetypal Yuweng Islet stratum can be found on Tongpan Islet. In the picture provided, the yellow layer is indicative of shale bedding beneath the basalt. It is representative of the most common basalt type in Penghu that is characterized by a high percentage of silica content. In this close shot of Tongpan Islet, the columnar jointed basalt has been transformed into cylindrical shapes by weather and erosion.

5-3. Basalt Joints of Penghu

The most unique feature of basalt is its pentagonal or hexagonal structure developed during the cooling and contraction of lava. This kind of crack structure is known as jointed columnar. Other varieties include plate-shaped and flaked jointed columnar.

The Penghu Islands is the only area in Taiwan that contains basalt, and the county was designated as a national reserve by the government in 1995.
 

5-3-1: Captions

• A view of the columnar jointed basalt and adjacent gravel beach from Yuweng Islet (also known as Si Islet). Aclose shot of the sea cliff next to the Dachi coast on Yuweng Islet.
• Yellow-hued plate-shaped basalt and black-hued columnar basalt can be found on the cliffs of Dongji Islet.
• Granular and columnar basalt at the west cliffs of Dongji Islet. 
• Mao Islet is a conservation area for sea birds and terns. The island is constructed by basalt and lava fragments, and sea caves can be found under its west cliffs.
• Cliffs made of columnar jointed basalt in northwestern Niao Islet. A close shot of the sea caves in northeastern Niao Islet.
• A different stretch of basalt jointed columnar can be found at the Great Stone-Lion Recreation Area on Qimei Island. The Waiting-for-Husband Rock, another unique lava formation on Qimei, was created by two basaltic dikes.
• Toujin Islet, a popular summer breeding spot for great crested terns, is an islet formed by basaltic dikes and volcanic breccia. 
• The Pleated Skirt formation on the northern shore of Yuanbei Islet is an example of tower-shaped basalt. A portion of the formation has been weathered down to cylindrical and plated shapes.
• The back side of the Whale Cave in Hsiaomen Islet.

5-4. Penghu Columnar Basalt Nature Reserve

Under the Cultural Heritage Preservation Act, the three islets of Xiaobaisha, Jishan, and Dinggou were declared part of a national nature reserve in 1992:

5-4-1. Xiaobaisha Islet

Named after its vast southern beach of white sand, the Xiaobaisha Islet includes columnar jointed basalt, unique tower-shaped basalt, and curved basalt formations. The islet’s plateau is covered with basaltic dikes and has an appearance similar to a volcanic opening.

The islet was formed by volcanic lava and rocks that were ejected from the ocean floor following a volcanic eruption about 13.2 million years ago. Today, Xiaobaisha Islet is included in the Reserve for its unique curvaceous columnar basalt formations. The islet is also a haven for breeding terns during the summer.

Caption: The unique curvaceous columnar basalt formations on the east coast of Xiaobaisha Islet.

5-4-2. Jishan Islet

The Jishan Islet comprises of two islets that differ in size. One is larger in size and the two islets are connected. Formed 12.2 million years ago, Jishan boasts magnificent columnar jointed basalt towers of various heights.

Captions:

The magnificent columnar jointed basalt towers of Lesser Jishan Islet.

Slanted columnar jointed basalt formations on Greater Jishan Islet.

5-4-3. Dinggou Islet

Formed over 11.8 million years ago,Dinggou Islet has an elevated and difficult terrain. The columnar jointed basalt cliffs on Dinggou have been eroded by the sea, forming clusters of sea stacks and individual basalt towers that point to the sky. Steep cliffs hamper human access, making Dinggou and its fellow islets a summer breeding haven for protected bird species, especially terns.

Caption:

Slantedcolumnar jointed basalt formations on Dinggou Islet.

5-5. Future Prospects

Both natural and cultural heritage sites can be found in Penghu Islands. Such unique basalt landscapes are of universal value and should be considered a national asset of Taiwan. Inclusion to UNESCO’s world heritage register would afford the Penghu Columnar Basalt Nature Reserve better protection and preservation, and help ensure that the magnificent basalt landscapes will continue to be protected and cherished by the world.  

1. National Museum of Natural Science

2. Geodiversity Database of Penghu