trapped air bubbles

Question
I have a 1 1/2 gallon tank with 1 betta in it that came with an undergravel filter.  It has 1 plant, 1 rock and 1 1/2 inches of gravel on top of the plate. The air pump appears to be working well, but the last 2 days I have noticed large air bubbles being released from the gravel spontaneously several times a day.  These are in a completely different area from the air stone/tube.  It seems to me that this air is trapped underneath the plate, but I don't know why or if it is a problem (or could cause a problem). I have had another betta in the same tank/setup for 9 months and have never seen this before.  ?

Answer
Dear Catherine,
It certainly could be air bubbles trapped under the plate. I bet it could be that small airbubbles from the airstone are collecting and forming one large bubble and then making it up out of the gravel plate. And the airstone could be releasing bubbles underneath the plate. If maybe you raised the airstone a little above then it should solve your problem.

I hope this helps!
Karen~