The description of the demise of Moronihah is fascinating because the earth is “carried up,” and “in the place of the city there became a great mountain.” Earthquakes can cause relocations of land, but hardly the rapid creation of “a great mountain.” It would appear that the best physical explanation for the destruction of Moronihah is that it was the site of a monogenetic volcano. This is a type of volcano that is created in a single eruptive event. The most recent example of this type was the eruption of Paricutin in Mexico:
“Rarely do volcanologist get to watch the birth, growth, and death of a volcano. Paricutin provided such an opportunity. The eruption that created Paricutin began in 1943 and continued to 1952. Most of the explosive activity was during the first year of the eruption when the cone grew to 1,100 feet (336 m). The cone continued to grow for another 8 years but added only another 290 feet (88 m). Effusive activity began on the second day and continued to the end of the eruption. Lava flows covered about 10 square miles (25 square km) and had a volume of about 0.3 cubic miles (1.4 cubic km). The rate of eruption declined steadily until the last 6 months of the eruption when violent explosions were frequent and violent.” (http://volcano.und.nodak.edu/vwdocs/volc_images/img_paricutin.html)
While even Paricutin was not an overnight phenomenon, it certainly is an accurate description of a volcano that grew up into a mountain. When we remember that Nephi is not describing the events of a single time period, it is easy to see how the final disposition of Moronihah would have been included as part of his set of original destructions.
Literary: Verses 9 and 10 both describe literal events, but they are placed in deliberate parallel. In verse 9 we have a city that sinks under water, and in verse 10 land is “carried up” over a different city. Regardless of the event, the typology is to show the extremes of the destruction. Water and earth both destroy, and in cities are in places they should not be. In verse nine Moroni sinks down, in verse 10 a mountain rises up in the place of Moronihah.
This same set with its reverse parallel imagery is found in 3 Nephi 9:4-5. Since this particular text had to have been written after the words of the Savior noted in chapter 9, Nephi appears to have selected these two descriptions from the Savior’s words, and moved them here as part of the catalogue of physical destruction.
Geographic: The geographic location of the city of Moronihah is not determined in the Book of Mormon, but it is referenced along with cities of the land southward, and just prior to the discussion of then lands northward, so it would be logical that Moronihah is a city in the lands southward (John L. Sorenson. The Geography of the Book of Mormon Events: A Source Book. FARMS 1990, p. 307-8)