Moods can be harder to identify their trigger. Usually when we have an emotion we can say what produced it. We can specify the event that triggered it, that brought our emotion forth. Often with a mood we can't. We wake up in an irritable mood or in a very positive mood; we wake up very apprehensive or sad, for no reason that we know.
Moods can evolve from a series of emotions or from a a very dense emotional experience. If we experience amusement again and again in a short period of time, the consequence will be a very euphoric mood. If we are furious again and again, we will then have a long period in which we are irritable.