How can this phenonmenon be explained?

Question

A bad of potato chips at an ocean beach is taken on a picnic in the mountains. You notice the bag starts to inflate almost to the point of bursting. Why does this occur?

Answer 1

Differences in pressure inside and outside the bag of potato chips.

Answer 2

Boyle's Law: Pressure and Volume are inversely proportional

Since the pressure on the mountain top is lower than at sea level, the volume of the air packaged with the chips will be larger. If the bag isn't strong enough, it will burst.