Samuel the Lamanite had prophesied these particular signs of the Savior’s death, and Nephi has phrased his description to echo and fulfill Samuel’s prophecy:
Yea, at the time that he shall yield up the ghost there shall be thunderings and lightnings for the space of many hours, and the earth shall shake and tremble; and the rocks which are upon the face of this earth, which are both above the earth and beneath, which ye know at this time are solid, or the more part of it is one solid mass, shall be broken up;
Yea, they shall be rent in twain, and shall ever after be found in seams and in cracks, and in broken fragments upon the face of the whole earth, yea, both above the earth and beneath.
And behold, there shall be great tempests, and there shall be many mountains laid low, like unto a valley, and there shall be many places which are now called valleys which shall become mountains, whose height is great.
And many highways shall be broken up, and many cities shall become desolate. (Hel. 14:21–24)
Conspicuous parallels between Samuel’s prophecy and Nephi’s report are “thunderings and lightnings,” the “seams and cracks” of the rocks, and the broken highways. Samuel had described “mountains made low,” almost certainly an allusion to Isaiah 40.
Geology: Convulsive earth movements frequently accompany an explosive volcano. The force of the explosion and/or the accompanying earthquake would break up rocks, and open “seams and cracks” into which fragments would fall.