Fresh vs. Salt Water: Unmixable Conditions Explained

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Discussion Overview

The discussion centers on the conditions that prevent fresh and salt water from mixing, particularly in underwater environments. Participants explore the physical principles behind this phenomenon, including density differences and diffusion processes.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that oceanic water has a higher salt concentration and density than fresh water, prompting the question of what keeps them from mixing.
  • Another participant explains that while fresh and salt water do mix, the process is slow due to density differences, with diffusion occurring primarily at the boundary between the two types of water.
  • A question is raised about the rate of mixing, specifically how slowly the mixing occurs.
  • A later reply suggests that the rate of mixing depends on various factors, including salinity differences, layer thickness, and temperature, potentially ranging from minutes to years.

Areas of Agreement / Disagreement

Participants generally agree that fresh and salt water do not mix rapidly due to density differences, but there is no consensus on the specifics of the mixing rate or the conditions affecting it.

Contextual Notes

The discussion highlights several factors influencing the mixing process, including salinity, layer thickness, and temperature, but does not resolve the complexities or provide definitive answers regarding the rates of mixing.

Who May Find This Useful

This discussion may be of interest to those studying fluid dynamics, environmental science, or anyone curious about oceanography and the behavior of different water types.

flatmaster
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oceanic water obviously has a higher salt concentration and is more dense than fresh water. What specific conditions keep these two from mixing? On discovery, I see underwater caves where salty and fresh waters don't mix. What's behind this? Should we integrate their schools?
 
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They mix, but slowly, as different densities help them keep separated and the only process that takes place - diffusion - is slow and occurs only on the boundary between fresh and salty water. They will mix much faster when stirred, as the surface between both waters becomes much larger.
 
How slowly is slowly?
 
Good question, one that I don't know answer to. It will depend on many factors - difference in salinity, thickness of the layers, temperature. Probably minutes to years depending on the circumstances.
 

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