Video of a turbidity current!!
This is the coolest thing I have seen in a long time – thanks to Dave Petley for the link. This event occurred in Cabo San Lucas, on the southern tip of the Baja California peninsula in Mexico. I imagine that these divers were reef-diving (as evidenced by the angelfish in the first few seconds of the video). This turbidity current starts out as a small flow on a very steep slope (more than 30 degrees) and is quickly overtaken by the main part of the flow. The real action starts then, as this current is moving very fast (more on speeds below), and it much thicker and turbulent. This flow quickly overtakes the scuba divers and keeps flowing downslope. You can see in the video that the flow keeps thickening with time, entraining the surrounding seawater (here is a paper about how hard it is to model entrainment).
I ballpark this flow to be moving about 5 m/s, or about 10 mph (from my rough estimates of distance in the video), which is similar to turbidity currents measured in nature. Jingping Xu measured currents with instruments in Monterey canyon at 2.8 m/s, and numerous papers measuring submarine cable breaks estimate speeds from 5 to 25 m/s. It is important to note that velocity and speed are two different things, and that shear stress is more important than either when discussing sediment movement (i.e. erosion and deposition) associated with turbidity currents. More on that in another post. For now, just enjoy the turbidity current – click this image to see the video – I cant figure out how to embed the video…
Here is the link in case you need it - http://www.liveleak.com/view?i=c45_1342620679. This is awesome.