If you look closely at the first shot of the volcano erupting, you can see office buildings far in the distance in the lower left-hand corner of the picture. This clip is used again near the end of the episode after the Professor's bomb detonates and the fire retreats into the volcano.
In the closing scene, Gilligan's drops his two buckets of water which trigger another jet of steam from the ground behind him. The steam is released too early -- before the buckets actually hit the ground.