Xiaomen Natural Monument Introduction
Xiaomenyu is surrounded by the sea, and over time, it has been sculpted into diverse coastal erosion formations due to the effects of waves and tides. Among these formations, the "Whale Cave" is an easily accessible tidal arch that can be observed in Penghu. Its formation is the result of erosion by sea waves, which have hollowed out the sea cliff, creating a tunnel-like structure, hence the name tidal arch. If you walk inside the cave, you can also hear the stunning sounds of the crashing waves. Additionally, on the coastal trail next to the island, there is a rock wall with clearly exposed and complete rock layers. From top to bottom, these consist of 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 real-world material for understanding the evolution of coastal erosion and geological processes. Therefore, both have been designated as natural monuments of Xiaomen. The Xiaomen area is also famous for the "Xiaomenyu Formation," which can be divided into an upper and lower layer based on geological analysis. The upper layer is composed of biological shell limestone, made up of the remains of shell organisms, quartz grains, and small foraminifera binding together. The lower layer consists of iron-bearing quartz sandstone or interbedded sand and mudstone, which are clearly exposed rock layers due to weathering. Because this geological feature is most complete in the Xiaomen area, it has been named the "Xiaomenyu Formation."
