Last December, around 100 tourists set out for New Zealand's Whakaari/White Island, where an active volcano has attracted hundreds of thousands of vacationers since the early 1990s. It was supposed to be a routine six-hour tour, including the highlight: a quick hike into the island's otherworldly caldera. Then the volcano exploded. What happened next reveals troubling questions about the risks we're willing to take when lives hang in the balance.