After visiting Yangmingshan National Park, my wife and I continued our Taiwan vacation at Yehliu Geopark. Although there was much to see on this stretch of the northeastern coast, it’s best known for the fascinating rock formations that have been shaped by millions of years of weathering.
The rocks at Yehliu are part of the Taliao Formation, deposited in a shallow sea environment during the Miocene Epoch (between 23 and 5 million years ago). Since then the land has risen relative to the sea, exposing the marine sediments. These rocks are made up of interbedded sandstone and mudstone layers of varying thickness. The sandstone is bioturbated and filled not only with fossils of marine invertebrates, but remnants of their burrows and tracks as well.
Sandstone is relatively resistant to weathering, while mudstone is not. Within the sandstone, the fossil tracks and burrows also create uneven areas of strength and weakness. Over the last few million years waves, wind, rain, and sun have worked away at these rocks of varying hardness, leading to differential weathering.
Hoodoos (“mushroom rocks”) are the most obvious example of this differential weathering. Harder concentrations of rock form the capstones while softer areas are eroded:
The weathered shapes are sometimes more elaborate:
On flat surfaces this weathering leads to potholes. These often harbor crabs and other organisms:
Seawater also works away at the rock on a smaller scale through salt heaving. The water deposits salt in the pores of the rock, and after drying it crystallizes and breaks apart mineral grains. This can lead to honeycomb weathering:
Weathering rings are also common where iron-rich minerals have oxidized:
Although the rocks took center stage at Yehliu, there were also some interesting organisms to be found. This plant featured some sharp serrations along its sword-like leaves:
There were also some beautiful birds…
…and birds eating insects:
As is often the case in Japanese-influenced Taiwan, cartoon characters were to be found even here:
Yehliu is a great concentration of fascinating geology, plants, wildlife, coastline, mountains, and culture all in one relatively small area. More than any other place we went in northern Taiwan, I strongly recommend this location as a “must-see.”
Hong, E. and E. Huang. 2001. Formation of the Pedestal Rocks in the Taliao Formation, Northern Coast of Taiwan. Western Pacific Earth Sciences 1:99-106.