A lake transformed by fire
Before 1996, Karymsky Lake was a clear, freshwater body inside the Akademia Nauk caldera on Russia's Kamchatka Peninsula. That changed dramatically on January 2, 1996. Following a series of powerful earthquakes, a new eruptive cycle began. In a rare and violent display, eruptions occurred simultaneously from two vents 6 km apart. Andesitic ash erupted from the summit of Karymsky volcano, while a new crater opened on the floor of Karymsky Lake, unleashing a powerful underwater, phreatomagmatic eruption.
For 18 hours, the lake churned. Explosive pulses from the lakebed shot columns of steam and ash into the air every five to six minutes. The event dumped between 30 and 40 million tons of pyroclastic material directly into the water. The eruption also triggered a tsunami within the lake, with waves reaching up to 20 meters (65 feet) high, powerful enough to fell trees along the shoreline. In less than a day, the once-normal lake was transformed into one of the world's largest natural reservoirs of acidic water. The event was so powerful it killed nearly all life within the lake's ecosystem.
The chemistry of a turquoise cauldron
The 1996 eruption radically altered the lake's chemistry. The massive injection of hot volcanic material and gases—high in sodium, sulfates, calcium, and magnesium—caused the lake's pH to plummet from a neutral 7.5 to a highly acidic 3.2. The water temperature also increased dramatically. This chemical soup is responsible for the lake's striking turquoise color. The bright color is not from biological sources, but from fine particles of sulfur and other volcanic minerals suspended in the water, which scatter light.
The acidity is maintained by continuous hydrothermal activity. Vents on the lake floor release hot, mineral-rich fluids and volcanic gases. Temperatures at some of these ascending springs have been measured at 92-97°C. These inputs keep the lake's water saturated with dissolved elements, effectively creating a hot, acidic broth that actively dissolves the surrounding volcanic rock. Although the pH level has slowly risen since the 1996 eruption, by 2012 the lake was still three times saltier than it was before the event. The volcano is one of the most active on the Kamchatka Peninsula, with its last eruptive period ending in 1982 after a decade of frequent activity.