The authorities who manage Kronotsky and the scientists who study it are sensitive to the downside of such tourism. Everybody leaves a footprint of some sort, the crucial questions being how deep and how many. At the beginning and the end of each summer season, investigators look for impacts at the caldera and the geysers. Their report helps inform decisions about the next season's visitation limits and dates. But the greater conundrum of Kronotsky, the one that provokes thought and not just sour belly, is how the concern over human-caused degradation should be reconciled with the inherent, violent dynamism of the place. This conundrum came to a point on June 3, 2007, when a massive wall of rock, mud, clay, and sand broke loose from a high ridge and slid, roaring, down a small creek valley, obliterating a hundred-foot waterfall, damming the Geysernaya River (all in a matter of seconds), and burying much of the Valley of Geysers beneath the resulting new lake. George Patton's army, march­ing through in hobnailed boots, couldn't have made such a mess.

Pervenets, Ustinova's firstborn geyser, is gone. So are a few other famous spouts. The rest remain. Vitrazh, the stained-glass mosaic, is intact. Alarming reports reached the international press, vacations were canceled, and people immediately disagreed about whether the slide was a tragedy or simply a fascinating natural shrug. "We scientists believe we are quite lucky to witness such an event," according to Alexander Petrovich Nikanorov, a researcher who briefed me at the zapovednik headquarters near Petropavlovsk. "Our lives are very short, and yet we witnessed it."

Geologists have good reason to feel that their lives, relative to the phenomena they study, are short. Rock usually moves slowly through time. But of course it's true for the rest of us also: Life is short, the world is big, and we're lucky to witness as much as we can. Whether that means we should all climb aboard the helicopter is another question, which I can't answer, not even to my own satisfaction. What I can tell you (and what Michael Melford's photographs show you) is this: Kronotsky Zapovednik is an extraordinary place, fragile and magnificent and changeable. Maybe you can take that on faith?