In Mosiah 18:32 it says that King Noah "discovered a movement among his people," so he sent his servants to watch them. And when they were assembling, they were "discovered unto the king." This verse has traditionally been read to mean that the king's men discovered Alma and his followers assembled in the place of Mormon. However, this verse could also mean that the servants of the king spied on a group of Alma's followers meeting within the local lands of Lehi-Nephi, and after interrogating them, learned more about the distant location of Alma and his followers at the waters of Mormon.
Noah sent an army to destroy Alma's group (Mosiah 18:33). The army apparently had some distance to go because of two reasons: (1) it seems that Alma's group did not realize they had been discovered until the army was assembled and on its way (Mosiah 18:34), and (2) apparently after the army had begun its march, Alma's group of 450 still had time to gather their flocks, assemble their goods and depart, outdistancing the pursuit of the military so that Noah's army "searched in vain" (Mosiah 19:1). [Alan C. Miner, Personal Notes] [See the commentary on Mosiah 18:4, Alma 5:3]
Geographical [Theory Map]: Mosiah 18:30--19:1; 23:1-20 Noah's Army Approaches--Alma Flees to Helam (Year 462)
Mosiah 18:30 19:1: 23:1-20: Noah's army approaches -- Alma Flees to Helam. ([Illustration]) [John L. Sorenson]