Undersea rivers we know little about | Hacker News Reader

Undersea rivers we know little about

bbc.com

108 pointshappy-go-lucky24 comments

I immediately thought of Devil's Kettle Falls reading this. I had to Google it and found that 4 months ago scientist have decided it flows back into itself. They have a plan to put a large amount of dye in during low water and see where it reconnects.

Ah the circular river. Very rare but useful to extract energy from.

Have people done this?

I'm quite certain the GP was a joke.

Only badly worded. The missing water flows back into the visible river somewhere downstream, not upstream.

Yes: http://www.mcescher.com/gallery/recognition-success/waterfal...

Does extracting energy from a circular river affect it's ability to continue being a circular river?

Just a river with an island, in a topological sense.

Well an underground volcano or something could inject energy into the system so you are probably ok, thermodynamically.

most rivers are circular - just that the upstream water flow is invisible, by virtue of being in water vapor form.

That's very deep. I'm impressed. Sincerely.

But is it true? The flow rate of the Mississippi (I got ~500 cubic km/year) is about 0.025 Great Lakes (20,000 cubic km combined) per year.

The oceans are 1.37 billion cubic km.

Yes, it's true. Most of the water that flows from the Mississippi into the Gulf of Mexico comes from rain. And most of that rain comes from ocean evaporation. Sure, there's some input from aquifers, and some recharging of aquifers. And there's evaporation from the Mississippi, its tributaries, and all of the associated lakes, wetlands, and so forth.

But the fact remains that the Mississippi is part of the global water cycle. And cycles are circles.

I sort of assumed that knowledge of the water cycle was a given.

But how fast does the water have to cycle for a named river to be part of a circle? Does once every 10 million years do it?

That's a fair point :)

Not circular, just rejoins downstream after the split.

Indeed. This article describes things further:

http://www.startribune.com/scientists-think-they-ve-solved-t...

We know lots about these things - as the article explains. A lab I'm roughly associated with models them, here's an example: https://www.youtube.com/watch?v=UR5NoaqpCok

The physics (IIRC) are very similar to snow avalanches. I saw a talk once that presented evidence of one in the Indian Ocean flowed half way to the Antarctic (order 1000s of km). They have been observed to scour the canyons (such as Monterey Canyon) and are hypothesized to be set up similarly to avalanches, where the sediment depositions become unstable and slide.

A final bit of trivia: the photo of the mooring base shows a common oceanographic mooring construction material - used railroad car wheels. Big, super heavy and relatively cheap. I've never heard of them being recovered. Usually the important parts are detached and the wheels are left behind.

I was curious about the canyon after looking at geo maps a couple of years ago. When I looked at Wikipedia at that time, it described the canyon as an ancient feature created by a long-ago river.

Is this stuff undergoing a revolution in understanding? Or was Wikipedia just very out of date? Revolutions in understandings are always fun!

The canyon is certainly an 'ancient' feature - just the underwater extension of geographic features on land. The river (on land) at the base of the canyon carries sediments into the ocean. These get deposited somewhat haphazardly, and occasionally destabilize forming the turbidity current. That is the extent of my understanding.

My first thought was that these formed during glaciation when most of the continental shelf was exposed. The rivers just had to flow further to get to the sea. My second thought is that my first thought is still valid after reading the entire article. It is interesting that they have mud flows in those areas, but I doubt that has much to do with how they formed.

Sea level during the Pleistocene glaciation got to be ~150 m lower than today. You are absolutely right that during times of low sea level, the rivers eroded this part of the shelf just as today. However, these canyons go all the way down the continental slope to ~3000 m below current sea level, with the same basic erosional forms (check out Monterey Canyon in Google Earth, it's gorgeous). These mud flows (called turbidites in the literature) are quite capable of eroding the seafloor when they flow down steep slopes, though at rates well below what rivers do on the surface.

Detroit at one time had seven rivers, but they were buried. In Detroit they're known as ghost waters.

http://www.huffingtonpost.com/2013/04/02/detroits-ghost-wate...

Hudson Canyon always fascinated me: https://en.wikipedia.org/wiki/Hudson_Canyon

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