Does "influx" require that whatever is coming in have come from somewhere else?

Question

I recently encountered a usage of the word "influx" that I found questionable:

The mayor promised to investigate the influx of crime to the area.

My first thought was that the writer should have used "increase," because all of the crimes referred to in the article were local people doing bad things to other local people.

Definitions of influx that I read in various sources (Merriam-Webster, Oxford Living Dictionary, and others), all refer to the arrival of (usually large) groups of people, or sometimes water coming in to an area.

The question that arose when I thought more about the word "influx" was whether it can be used in a situation where something arises out of nowhere, or from something like a chemical reaction (rather than a place), or does whatever/whoever is arriving have to come from somewhere? My ear/brain/gut all agree that the arriving water/people have to come from somewhere, but I can't say why.

An example of the usage where something arises not from another place could be:

The chemical reaction caused an influx of toxic gases.

It sounds odd, but I can't say why, and I'm hoping someone else can.

Answer 1

The Merriam-Webster page that you link includes a list of synonyms that includes inflow. That is an extremely close synonym, flow being the English verb of choice for translating the Latin fluere, which you will find lurking in the etymology there. The abstract nouns influx and inflow are merely nominalizations of the verbs influere and flow in. The key point here is that these are both verbs of motion, the in being the destination or direction of that motion. So we are talking about a flow of something to the inside of some space, and yes it follows that this motion must be from outside that space.