Taiwanese Typhoons Trigger Turbidites
These sedimentary layers are turbidites, the remnant of ancient debris flows underwater. Turbidites are the main way that sediment deposited in the shallow water near a continent makes its way into the deep ocean. Rivers and streams bring sediment to the ocean and deposit it near the shore, and then eventually so much sediment is deposited near the shore that it becomes unstable and slides down to the deeper part of the ocean, often in submarine channels.
Turbidites can be recognized in sedimentary layers by what is known as the Bouma sequence – a classic pattern where the coarsest grained sediment is at the bottom and the sediment gets finer to the top. In this sequence, the big brown layers are sandy, while they thinner dark layers are silt to clay. These turbidites started as flows of sand and silt moving cascading down from shallow water to deep water. The heavier sand stayed at the bottom of the flow, forming the sandy layer, while the silt and clay were suspended above the flow and only settled out into layers after the flow stopped.
Scientists at Tongji University in Shanghai just published an interesting study regarding turbidites in Taiwan. Turbidites can be triggered by many things; weather on shore, earthquakes, or just random events. Over a 3.5 year period from 2013 to 2016, an area of Taiwan that feeds into a submarine canyon known as the Gaoping Canyon received heavy rainfall from 16 typhoons. The scientists tracked turbidites in this area and found that 72% of the sediment delivered to this canyon as turbidites occurred during these storms. While this is not the case everywhere, at that particular spot, typhoons are therefore the main trigger of sediment moving into the deeper ocean.
-JBB
Image credit: https://flic.kr/p/UgSo
Reference: http://bit.ly/2vhdm1f
