Volcanoes go through periods of activity.
They may not be active for thousands, even millions, of years. In time, rainwater and melted snow can accumulate inside the crater, making a clear, beautiful lake.
Crater Lake in Oregon came into existence after the top of Mount Mazama collapsed and formed a huge caldera.
The caldera filled with water, creating an impressive lake at the top of the volcano’s steeply sloping sides.