Coalescence is called that phenomenon in which two bodies or materials can be united in one. The term is particularly used to refer to metals that go through a welding process, especially one that uses thermal action, generally called fusion welding, to heat the surface of both metal elements to such an extent that they are capable of melting the one with the other. It is with this process that the coalescence of partially fused metal grains can be achieved, with which a single crystalline system can be achieved. Followed by this, an epitaxial growth allows the crystalline coalescence and the molten materials to stay together superficially.
Within chemistry, it is known as coalescence those phase domains that have an identical composition, they join to become a larger phase domain. A simple example of this phenomenon is that of mercury, since when many drops coexist in the same space, they come together to form only one drop. Similarly, when shaking a container with water and oil, violently, you can see how they come together in small bubbles, and then separate into just one drop.
In physical geography, there is a phenomenon under the name of coalescence, in which, because of the rains that affect an area with abundant valleys or tectonic depressions, the flow of sediments is stimulated, which will be interspersed according to the torrent by the one that they mobilize. This, as time passes and various rainy seasons, will result in the crossed stratification of the place.
