The "crater" of Crater Lake is not a crater in the usual sense. It is a world-class example of a caldera, a volcanic feature that develops when a huge volume of ash explodes out of volcano, and the summit sinks into the void left behind. It was an unimaginable catastrophe. In the space of a few hours or days around 15 cubic miles of ash and debris were blasted into the atmosphere from the summit area of Mt. Mazama, the name given to the former volcano that became Crater Lake. What had once been a volcano as tall as 12,000 feet was now a smoking ruin with a rim barely exceeding 8,000 feet. The bottom of the caldera was another 4,000 feet lower. The ash was spread across the western United States and Canada, providing a crucial dating horizon for archaeologists (the ash has a unique chemical composition that can be identified in dig sites).
The Crater Lake caldera is young in the geologic sense, having erupted 7,700 years ago (+/- 150 years). Think about that: the ancestors of the indigenous people of the region saw and experienced this event. Their oral histories of the Klamath people recall the event. How many cultures in in today's world have collective memories that date back that far?
Tens of thousands of people on the island died from the eruption itself or starvation later (all vegetation on the island was destroyed). So much ash was blown into the atmosphere that the climate cooled to the extent that snow fell during the summer months over much of the northern hemisphere. Famine contributed to hundreds of thousands of deaths around the world.