Insights into Submarine Geohazards from Breaks in Subsea Telecommunication Cables

Abstract

The original discovery of active submarine landslides and turbidity currents in the deep ocean was made in the 1950s through analysis of breaks in transoceanic communications cables. Further insights regarding the causes, frequency, and behavior of damaging submarine flows are presented here, based on recent disruptions of modern communications cables in the Strait of Luzon off southern Taiwan. In 2006, the Pingtung earthquake triggered landslides and at least three sediment density flows (a general term covering turbidity currents and similar flows). These flows sped down submarine canyons and into the Manila Trench at 12.7–5.6 m s–1 (45–20 km h–1), resulting in 22 cable breaks. In 2009, the cables were again damaged, this time by extreme river discharge associated with Typhoon Morakot. Two cables were damaged during the main flood when debris-charged river waters dived to the seabed and down Gaoping Canyon. A second, more damaging sediment density flow formed three days later when river levels were near normal and seismic activity was low. It is suggested that this second flow resulted from deposited flood sediment that was remobilized possibly by internal wave activity. Further breaks were reported in 2010 and 2012. While historical cable break databases are incomplete, they imply that since at least 1989, density flows capable of breaking cables have been infrequent, but they increased markedly after the 2006 Pingtung earthquake—a time that coincided with a transition to more extreme rainfall associated with northward migration of typhoon tracks to Taiwan.

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