The Birth of Crater Lake

As Crater Lake National Park turns 112, we explore the devastating volcanic eruption that formed it 7,700 years ago.

By Caleb Diehl May 30, 2014

Paul Rockwood's depiction of the eruption of Mount Mazama 7,700 years ago

Clear to a depth of 40 feet, the tranquil waters of the Crater Lake Caldera hide a history of violence that may well resurface in years to come. The National Park’s 112-year anniversary passed on May 22, but its geologic story stretches back much further.

7,700 years ago, on the Northeast side of the volcanic cluster Mount Mazama, a single vent funneled pumice and ash into a towering, 30-mile high plume. In what would go down as the biggest volcanic event in North America in the last 10,000 years, 12 cubic miles of superheated ash and pumice avalanched onto the surrounding peaks. Winds spirited ash as far away as southern Canada. Burdened by the weight of magma, the volcano began to implode. Imagine an eruption about 30 times the size of that of Mount St. Helens in 1980.

As the summit of the great mountain crumbled, more magma erupted through cracks around the peak, filling the surrounding valleys with 300 feet of ash and pumice. Still more magma speeded the collapse. When all of that ash settled, there stood the caldera, five miles in diameter and one mile deep.

Then, new vents within the caldera erupted, spitting out the material for a central platform and Wizard Island. Water came next, from rain and snowmelt.

Since Congress declared the rectangular chunk of land around Crater Lake a National Park in 1902, its protected area has mushroomed from about 149 acres to 181,000 acres. Annual visitation stays at around a half million. 

A Crater Lake sunrise

Under blue summer skies, visitors won’t want to miss the 2.5-mile hike up Mount Scott. Part of the complex of cones that made up Mazama, the peak has escaped the obliteration of most of its neighbors. The 8,929-foot summit remains the highest point in the area. Hikers who climb past its Whitebark pines earn the park’s clearest view of Crater Lake—island, rim and water. 

Those hikers might not want to look for long. National Geographic has named Crater Lake the tenth most dangerous volcano in America. It turns out that volcanoes quiet for thousands of years have a habit of suddenly erupting again.

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