The 1837 edition changed the past-tense was to the present-tense is here in Alma 8:18. This change in tense appears to be unintentional. It was not marked by Joseph Smith in the printer’s manuscript. Moreover, the Book of Mormon text consistently prefers past-tense verb forms within past-tense narrative descriptions, including references to geographical location, as in the following example that involves the noun borders:
As discussed under that passage, every narrative that gives the geographical position with respect to the borders of some place uses the past tense, not the present tense. Here are some additional geographical examples involving words other than borders (such as way, land, and pass) that take the past tense:
For the example in Alma 43:5, the past-tense was was accidentally replaced by the present-tense is in the 1841 British edition; this change in tense has been maintained in the LDS text.
Summary: Restore the past-tense was in the geographical description found in the past-tense narrative of Alma 8:18.