A Beautiful Channel

Today our survey took us over this lovely, meandering submarine channel:

SeaBeam image of a portion of a submarine channel off the coast of Sao Luis, Brazil

It is one of several channels at the distal end of a small lobe of a submarine fan that is located offshore of Sao Luis, Brazil. The channel is probably ultimately fed by the rivers that drain the province of Maranhao (the Grajau, Pindare, Mearim, and others) and that empty into the Atlantic Ocean near Sao Luis.

The submarine fan in this area is nowhere near the same scale as that of the Amazon fan. Still, this channel seems worthy of note -- at least to a sedimentologist like me, who loves rivers! After all, this channel may be under a couple thousand meters of water, but it has meanders, it channels water down slope, and is in many ways similar to continent-bound rivers. Sort of . . .

Notice, for example, the narrow ridges that line the channel. These ridges are levees. They are produced by overbank flow (flow that is too large to be confined to the channel, hence spills out over the top and onto the surrounding surfaces), just like levees in river systems on land.

Also notice the large, curved, slump features on the right side of the channel (in the green/blue shaded area). Although slumping does occur on the cutbanks of rivers on dry land, it is even more common in submarine channels, where all of the sediments are saturated with water.

We don't know how old this features is, but we cored close to it so we may be able to determine its age when we analyze the sediments. In any case, it really is a beautiful feature.

Isn't geology fun?!