An enormous eruption 7,700 years ago created Crater Lake, when massive pressure under the 12,000 foot Mount Mazama caused a circle of vents to form and started to spew lava. Eventually, enough vents formed around the mountain in a circular pattern and when enough lava flowed out, the entire top of the mountain collapsed and formed a deep, circular hole. Over time, rain water filled the hole to create a lake.
Read more
