The Changyun Ridge, a shelf sand ridge located off the western coast of Taiwan, is a tide-dominated sand body. This ridge is defined by the 50-m isobath and consists of two smaller ridges. The eastern Changyun Ridge is about 65 km long and 15 km wide and approximately parallel to the western shoreline of Taiwan. The western Changyun Ridge has a length of 53 km and a maximum width of 26 km, trending northwest-southeast normal to the Taiwan western coast. The eastern ridge has morphologic characteristics similar to those of typical linear sand ridges. Tidal currents show distinct bidirectional patterns with speeds exceeding 100 cm s⁻¹ strong enough to move sandy sediments. Large to very large sand waves occur on the western Changyun Ridge and sand waves seldom appear on the eastern Changyun Ridge, implying that the former is presently active while the latter becomes inactive or moribund. The configuration and distribution of these two ridges further suggest that the ridges developed sequentially from near-shore to offshore, presumably in response to a westward progressive decrease in velocity and change of flow direction of the north-flowing tidal currents.