the.com/crater lake

means A deep, strikingly blue lake that fills the collapsed basin (a caldera) left when a volcano's summit erupted violently and then fell in on itself.

from The name is plainly descriptive: Crater Lake in Oregon formed about 7,700 years ago when the volcano Mount Mazama erupted catastrophically and then collapsed inward, leaving a huge caldera that slowly filled with rainwater and snowmelt. Early settlers and explorers simply named it for what it looked like — a lake sitting inside a crater — and the term 'crater lake' became the general geological name for any lake that forms this way, in calderas or volcanic craters worldwide. 'Crater' itself traces back to Greek 'krater,' a wide mixing bowl for diluting wine with water, a fitting image for a giant bowl later filled by nature.