According to Alvin Benson, since the verb disperse implies breaking up and scattering, the terminology in 3 Nephi 10:9, "the darkness dispersed," could refer to the eventual dispersion of a volcanic ash cloud. That verse also indicates that the trembling of the earth continued throughout the three-day period of the Savior's entombment, suggesting continued volcanic activity and many aftershocks. Also, volcanic ash may have been coming forth all that time to sustain the thick darkness. [Alvin K. Benson, "Geological Upheaval and Darkness in 3 Nephi 8-10," in The Book of Mormon: 3 Nephi 9-30, This Is My Gospel, p. 65]
3 Nephi 10:9 The darkness dispersed . . . and the earth ceased to tremble ([Illustration]): Dark clouds block the light of the afternoon sun as a storm builds around Lake Atitlan in Guatemala. . . . Apparently during the three days of darkness, there were numerous aftershocks, for, in the morning, as the darkness began to disperse, "the rocks did cease to rend, and the dreadful groanings did cease." [Scot and Maurine Proctor, Light from the Dust, p. 167]