I think the character does double service in that it has meanings which are very much mouth-related - 薄口 (thin-mouthed - like weak taste) 後口 (after-mouth - after taste); but it also has a ton of meanings which are like opening / spout / hole / crater.

http://compling.hss.ntu.edu.sg/omw/cgi-bin/wn-gridx.cgi?usrn...

It's not that a land's-mouth is a crater, more like, mouth and opening are more synonymous in feeling in Japanese.

Almost certainly. One fascinating aspect of language is that many metaphors that are baked into language appear in many languages. E.g. In English we can form the future tense with modal verbs, "I will..." and "I am going to..." and in Chinese there are similar modal verbs "我要..." and "我去...". In both languages the idea of intention, or motion, are used as a metaphor in forming the future tense. Or 加油, an expression of encouragement similar to "put your foot on it" which has no equivalent in English, but does in Danish, "giv det gas".