The island of Taiwan (also known as Formosa by the Portuguese) is a relatively young, but immensely interesting geologic wonder. Pushed up out of the sea within the past 6 million years, Taiwan is an accretionary wedge that came to be as a result of sediment and rock being “scraped” off the top of the Eurasian plate as the Philippine plate both subducted under and over ran it. This unique situation came about as the edge of the Philippine plate (composed of dense, mafic materials) subducted under the Eurasian plate (composed of less dense, felsic materials). However, towards what is now southern Taiwan, the less dense Eurasian plate has been forced into subducting under the Philippine plate as the dense, mafic crust beneath the South China Sea was forced under the Luzon island arc, dragging the Eurasian plate with it.

 

This unique tectonic arrangement, combined with lateral compression from the collision of the volcanic Luzon island arc with the accretionary prisms of sediment and rock materials scraped off and uplifted during subduction over the past ~6 million years has been primarily responsible for forming the island and its several mountain ranges. This unique tectonic setting has also resulted in the islands mountain ranges displaying a full spectrum of the stages of orogenesis (mountain building). The ranges in northern Taiwan are no longer uplifting, but are rather in decline as weathering and erosion diminish them with out uplift to counter the loss of elevation. The ranges of central Taiwan are mature and tall, with their highest peak, Mt. Yushan, among the tallest mountains in east Asia. The southern reaches of Taiwan are just recently beginning to experience substantial orogenesis, and the nascent mountains threaten to touch the sky in a few million years. All this happening on an island with an area (~35,800 km²) about the same as Maryland (~32,800 km² counting its wet parts).

 

 

Of course, the fascinating tectonic setting of Taiwan doesn’t just produce beautiful mountains. Earthquakes born of the collisions between the lumbering tectonic plates and compressional forces acting on faults through out the island are an ever-present hazard. Among the worst was the 1999 Chichi earthquake, a 7.3 magnitude event that devastated the island. Around two and a half thousand people perished or were never found, almost twelve thousand were injured, and close to 10 billion USD in infrastructure and economic damage ensued. While earthquakes are a potentially devastating reality for those who call Taiwan home, much effort has been placed in engineering safer buildings and cities on the island. The best example being the former tallest building in the world, Taipei 101, built on foundation rollers, with reinforced steel frames, and with a self stabilizing 730 ton mass dampener to keep such a tall building from coming down in the event of a major earthquake.

Mass Dampener in Taipei 101. Image by Armand du Plessis