For more than half a million years, volcano Mount Mazama towered over southern Oregon. From time to time, it erupted, spreading pumice, ash, and cinders for miles around. Then, approximately 7,700 years ago, Mount Mazama erupted with such force that the volcano could no longer support itself and it collapsed, leaving a large caldera. Eventually, the volcanic action subsided and all was calm. Over the next centuries, water and snow accumulated in the caldera. In 1902, Crater Lake became a national park.