Blog from 18-Sep-10

Finding Safe Passage

Finding Safe Passage through an Undersea Mountain Range

Dives 1364 and 1365, 14-15 September 2010

Where on earth can you find a volcanically active valley full of unique life forms and smoking chimneys accessible only by crossing a treacherous mountain pass?

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Corals inhabit the rocky edge of a deep-sea crevasse on the volcanic slopes of Endeavour Ridge.

At Endeavour Ridge! Endeavour is a section of the Juan de Fuca Ridge, and part of the global 65000km mid-ocean ridge system, a continuous undersea mountain range along spreading tectonic plate boundaries. In our part of the northeast Pacific, the Juan de Fuca plate and the Pacific plate are moving away from one another leaving a rift along the boundary. New sea floor is constantly formed in the spreading centre where lava emerges from weak points in the oceanic crust. The area is characterized by high temperature hydrothermal vent fields with "black smokers" - chimney-like structures that emit superheated particle-laden water.

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Tube worms inhabit the exterior of a deep-sea mineral chimney formed by a hydrothermal vent in Endeavour Ridge's volcanic rift valley.

During our Fall 2010 installation cruise, we are venturing into this volatile terrain to install instrument platforms, video cameras, seismometers, a bottom-pressure recorder, an acoustic array and a water sampler. But how will we retrieve the data from all these instruments? It must be relayed by cable to Endeavour node, where it can then be transmitted through the existing NEPTUNE Canada cable network to the Internet.

This means that cable must be laid on the ocean floor 2km beneath the surface over an underwater mountain range!

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Rugged terrain on Endeavour Ridge.

Our first step in laying the cable was to conduct a survey of the bathymetry (i.e. the underwater depth map) to map the topography of the sea floor. Scientists used GIS (Geographical Information System) software to hand trace a potential route on bathymetry maps from previous international expeditions. Integrating knowledge of undersea terrain with survey maps and depth data is an art that requires specialized knowledge and experience - a task that can't be computer programmed!

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Screen capture from the Geographic Information System used to plan the cable route into Endeavour Ridge.

However, sometimes a road that looks like a paved four-lane highway on a map turns out to be a pitted gravel tractor trail in real-life, so we needed to check that the route was actually suitable for cable! Therefore, the next step was to fly the route with ROPOS, while surveying the bottom with a high resolution multibeam sonar.

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Screen capture from the geographic visualization system used for cable route planning.

For the trickiest parts, we crowded around the monitors in the operations room and watched live video from ROPOS's HD camera. There were some surprises along the way: steep slopes ripe for an underwater avalanche, knife-edged cliffs, deep crevasses and even some curious sea creatures.

Our survey continued well into the early-morning hours, but eventually everyone agreed on a safe mountain pass, for our first route. And so, we are ready to lay the cable!

Photo Slideshow

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