Kelut volcano has been notorious for the repeated ejection of crater-lake water during eruptions, producing devastating lahars. A series of tunnels and shafts were constructed in the 1920's to lower the lake level and reduce the hazards of eruptions. The initial tunnels lowered the lake level 50 m, but the 1951 eruption deepened the crater by 70 m, leaving 50 million cu m of water. Following another devastating eruption in 1966, lower outlet tunnels were constructed, and prior to the 1990 eruption the lake contained only 1 million cu m of water.
The turquoise waters of Yu-gama, one of three craters at the summit of Japan's Kusatsu-Shirane volcano, are a popular tourist destination. Yellow rafts of sulfur float on the surface of the acidic lake, which prior to an eruption in 1882, was clear, with forested walls. Frequent phreatic explosions have occurred from Yu-gama and the two other summit craters during historical time. This 1981 photo was taken from the south crater rim.
A geyser-like ejection of steam and ash rises above the surface of the crater lake of Poas volcano in July 1977. The white ring at the base of the eruption column is a steam cloud that is traveling laterally away from the vent along the surface of the crater lake. Mild phreatic explosions such as this one were typical of an eruption that began in May 1977 and lasted at least until July. The crater walls rise about 250 m above the lake.
A small phreatic eruption on February 29, 1980, produces a column of ash and steam above Ruapehu's Crater Lake. A darker central plug is surrounded by a white ring produced by pyroclastic surges traveling across the lake surface. This view is from the NW, with Mitre Peak at the upper left. A series of small phreatic explosions had begun December 5, 1979, and lasted until April 15 of the following year.
The interaction of magma and water can produce strong phreatic (steam-driven) explosions, such as seen in this 1980 photo of New Zealand's Ruapehu volcano. Clouds of ash and steam trail from large ejected blocks in the eruption column. Laterally moving pyroclastic-surge clouds form a white basal ring above the surface of a crater lake. Phreatic or phreatomagmatic explosions are common at submarine volcanoes, crater lakes, and other places where hot magma (or associated gases) encounters surface water or groundwater.
A surtseyan eruption on May 8, 1971, from Crater Lake at the summit of Ruapehu volcano in New Zealand ejects a dark column of ash, mud, and steam. Individual ejected blocks can be seen at the margins of the cloud, trailing cockscomb sprays of ash and steam. This type of euption column is typical of explosions that involve water-magma interaction.
This December 1971 photo shows a lava dome rising above the surface of a crater lake on Soufriere St. Vincent volcano in the West Indies. The lake temperature rose to 80 degrees Centigrade during extrusion of the dome, but despite the extrusion of new magma in the crater no explosive eruptions occurred during the eruption.