Volcanic ash piling on the ground and fumes filling the air. Some survivors of the eruption of Mount Ontake made a split-second decision to hide behind big rocks or escaped into lodges that dot the mountain's slopes. The experience she recalled on Tuesday and the accounts of others suggest that luck and instinct made the difference between life and death for the hikers who were in harm's way. Seismologists had detected signs of increased seismic activity at Mount Ontake, one of Japan's 110 active volcanos, but nothing signaled a fatal eruption. About 40 people took refuge at Arai's lodge for about an hour and a half, all of them staying on the first floor of the two-story building. A sixth sense seemed to help Hidenari Hayashi, a tour guide specializing in the central Japan mountains. Just as a cable car carrying his group departed the station closest to the summit, an explosion sounded, which Hayashi thought was thunder at first. Ogawa was shocked when she returned to her home in the Nagao prefecture and saw footage of the eruption on TV.