Xiaomen Natural Monument Introduction
Xiaomenyu is surrounded by the sea, shaped over time by waves and tides that have created a variety of marine erosion landscapes. Among them, the "Whale Cave" is a sea-eroded arch that is accessible in Penghu and easy to observe. Its formation is due to the erosion by ocean waves that have hollowed out the cliff, leading to its designation as a sea-eroded arch. If you venture inside the cave, you can also hear the powerful sounds of the waves. Additionally, the rock wall along the island trail reveals distinct and complete rock layers. From top to bottom, these include siliceous basalt columnar joints, peat layers, siltstone layers, and sulfur layers, known as the "Crater Lake Remains." Like the Whale Cave, it possesses rarity and uniqueness, making it an excellent practical resource for understanding the evolution of marine erosion and geological development, and both have been designated as natural monuments of Xiaomen. The area of Xiaomen is also famous for the "Xiaomenyu Formation," which can be divided into two layers based on geological age analysis. The upper layer consists of shell limestone formed from biological shell debris, quartz grains, and small foraminifera cemented together, while the lower layer is composed of interbedded iron-rich quartz sandstone or sandy mudstone, clearly exposed due to weathering. Because of these geological characteristics, the Xiaomen area exhibits the most complete exposure, hence named the "Xiaomenyu Formation."
