As explained under Alma 8:18, the Book of Mormon consistently uses past-tense verb forms to describe geographical location whenever the narrative as a whole is in the past tense. In this passage, the 1841 British edition replaced the original was with is; the LDS text has continued with this present-tense reading up through the current edition. The critical text will restore the original was.
Summary: Restore the original past-tense was here in Alma 43:5 since geographical location is characteristically referred to in the past tense in the Book of Mormon whenever the narrative itself is in the past tense.