Complex sentence: It is predicted that the Hilina slump is sliding seaward on top of the southern flank of the Kilauea volcano that composes the southeastern portion, about 13.7%, of the Big Island of Hawaii.
Split into simpler sentences: It is predicted that the Hilina slump is sliding seaward on top of the southern flank of the Kilauea volcano. Kilauea is the southeastern portion, about 13.7%, of the Big Island of Hawaii.