Question: In what year did the eruption occur that laid down the lava upon which a famous forest visible from the Tenjō-Yama Park Mt. Kachi Kachi Ropeway? 
Sentence (from "Aokigahara"): Aokigahara (青木ヶ原 ) , also known as the Suicide Forest or Sea of Trees (樹海 , Jukai ) , is a forest on the northwestern flank of Japan's Mount Fuji thriving on 30 square kilometers (12 square miles) of hardened lava laid down by the last major eruption of Mount Fuji in 864 CE.
Relevant evidence: Yes