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.