The allusion Alma makes to the Exodus is interesting. On one level he appears to be saying that since the Lord could work a miracle before, he could (and did) work on in the life of Alma the Younger. While that is the simplest explanation, it does not tell us why Alma selected this particular miracle. It is possible that there is more happening here.
First, there is the salvation of Israel coming out of water. Even though they were not in water, they are still symbolically passing through water, and therefore there is the possibility of a baptismal image. The second and more sure allusion is the elimination of the wicked Egyptians. Alma uses this experience as a miracle of salvation for the righteous and death to the unrighteous. He becomes part of the miracle for having become one of the saved righteous, rather than his previous course.