About 6,800 years ago, at the climax of a series of dramatic eruptions, the top of Mount Mazama collapsed and left behind the huge crater, or caldera, seen today. Before the caldera filled with water, more eruptions followed. The most striking evidence of this post-collapse volcanic activity is Wizard Island, a small volcano whose symmetrical cone was formed by a fountain of cinders erupting from the caldera floor. On the left side of the caldera, a similar cone appeared, but today it lies hidden 496 feet (151 m) below the lake surface. Geologists believe that lava flows erupting after the collapse helped seal the fractured caldera floor, allowing melting snow and rain to accumulate.