What is the difference between eluvium and alluvium?

Question

I was reading about kimberlite on Wikipedia and it mentioned eluvium. I've heard of alluvium, alluvial fans, alluvial deposits, etc. However, when I looked up eluvium, it sounded exactly like alluvium. Indeed, looking at the Wikipedia articles, the definitions sound identical to my (expertly untrained) ears: > **Alluvium:** loose, unconsolidated (not cemented together into > a solid rock) soil or sediments, which has been eroded, reshaped > by water in some form, and redeposited in a non-marine setting. > **Eluvium:** geological deposits and soils that are derived by in > situ weathering or weathering plus gravitational movement or > accumulation. So, both of these sound like soil and sediments, eroded and deposited. But obviously, they can't be the same thing. What's the difference? How can I tell the difference if I see it "in the wild"?

Answer 1

The difference is subtle but distinct. Alluvium is a sedimentary product of water transport. Eluvium has two definitions: 1) a sedimentation product of wind, as in fine sand deposited in a dune; and 2) a weathering product, or residue, consisting of rock debris produced " in place" (not necessarily having been transported) by disintegration or decomposition of rock.

There is another related, and confusing, term; "eluviation". This is the This is the downward movement of suspended material (aka. colloids) from one soil horizon into a lower soil horizon. Obviously, this would involve water as well.