Crater lakes are lakes that form in volcanic craters, calderas and maars.

Volcanic craters are circular depressions at the top of volcanoes caused by volcanic activity. Calderas are large craters formed by the collapse of land into a depression following a volcanic eruption. Maars are flat-bottomed volcanic craters formed by an explosion that occurs when groundwater comes into contact with hot lava or magma.

Crater Lake

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Crater Lake is a caldera lake located in Crater Lake National Park in Oregon, United States. It was formed when the volcano Mount Mazama collapsed in roughly 5,600 BC. Crater lake is 5 to 6 miles wide and its deepest point has been measured at 1,949 feet making it the 9th deepest lake in the world (Lake Baikal in Siberia is the deepest). Due to the fact that Crater Lake has no tributaries or inlets the water in the lake is exceptionally clean, pure and free of pollutants.

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Mount Pinatubo

Mount Pinatubo is an active stratovolcano located on the island of Luzon in the Philippines. 

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In June of 1991 Mount Pinatubo erupted and produced the second largest terrestrial eruption of the 20th century. The total volume of material erupted may have been up to 25 cubic kilometers and the removal of such large mass led to the formation of the large caldera that exists here today.

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Lake Albano

Lake Albano is a small volcanic crater lake in Lazio, Italy about 15 miles southeast of Rome. On a height overlooking it is Castel Gandolfo where the Pope has a villa and spends his summers. Lake Albano hosted the rowing and canoeing events during the 1960 Summer Olympic Games that were held at Rome.

Lago de Atitlán

Lago de Atitlán fills an enormous caldera that was formed 84,000 years ago by a volcanic eruption in the Highlands of Guatemala. It is believed to be the deepest lake in Central America. In 1976 a 7.5 magnitude earthquake struck Guatemala killing 26,000 people and fracturing the lake bed causing the level of the lake to drop 2 meters in one month.

Blue Lake

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Blue Lake is a large lake located in an extinct volcanic maar within the Mount Gambier maar complex in South Australia. It is one of two crater lakes located on Mount Gambier. Blue Lake is roughly 250 feet deep and is known for changing colors during the year. From December to March the lake turns to a vibrant cobalt blue and then changes to a colder steel grey color from April to November.

Heaven Lake

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Heaven Lake is a crater lake located within a caldera atop the volcanic Baekdu Mountain on the border between China and North Korea. The lake is located partly in Ryanggang Province, North Korea and partly in Jilin Province in northeastern China. The caldera that contains Heaven Lake was formed by a volcanic eruption in 969 AD. The lake is reportedly home to the Lake Tianchi Monsters, a group of Loch Ness-type creatures that have reportedly been seen living in the lake by hundreds of people.

Rano Kau

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Rano Kau is a large crater located in Rapa Nui National Park on Easter Island in the Pacific Ocean which contains a crater lake. Though Rano Kau is right on the coast of Easter Island and the Pacific Ocean the water in the lake is fresh. Only three bodies of water on the island are fresh water. Rano Kau is estimated to be 150,000 to 210,000 years old.

Lake Nyos

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Lake Nyos is a crater lake located in the Northwest Province of Cameroon. A pocket of magma lies beneath Lake Nyos and leaks carbon dioxide (CO2) into the water which changes it into carbonic acid which is deadly. On August 21, 1986 the lake suddenly emitted a large cloud of CO2 which killed 1,700 people and 3,500 livestock in nearby villages.

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To prevent another disaster a large tube was installed into the bottom of the lake to allow CO2 to leak out of the lake in safe quantities and prevent another large buildup but whether this will work going forward is unknown.

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Lake Nyos also posses another natural threat as one of its walls is weakening and could eventually give way causing massive flooding which could reach as far as Nigeria.

Lake Mashu

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Lake Mashu is a crater lake formed in the caldera of a dormant volcano and is located in Akan National Park on the island of Hokkaido, Japan. Lake Mashu has no significant inlets and no outlet and in 1931 the transparency of the water was measured at 41.6 metres compared to Lake Baikal which measured 40.5 metres around the same time. Based upon those numbers, Lake Mashu was considered the clearest lake in the world though it is highly doubtful that it is the clearest lake in the world today since salmon and rainbow trout have since been introduced to the lake. The Japanese consider Lake Mashu to be mysterious since it is often shrouded in fog in the summer.

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Mount Cleveland, Alaska

Perhaps the next spectacular crater lake in the forming.

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