Just inland from the Pacific coast of El Salvador, the striking blue waters of Lake Coatepeque fill part of a caldera of the same name. An astronaut aboard the International Space Station took this photo of the lake and surrounding terrain on February 10, 2026, as the station passed over Central America.
The caldera formed during a series of explosive eruptions between 72,000 and 51,000 years ago. After the caldera’s formation, additional eruptions produced several lava domes along its western side, including one that became Isla del Cerro (Isla Teopán). According to the Smithsonian Institution’s Global Volcanism Program, there have been no reported eruptions from the caldera during the Holocene (the past 11,700 years).
Today, homes, restaurants, boathouses, and other structures line the lakeshore. This human footprint extends westward toward the caldera’s steep rim, which abuts the eastern flank of Santa Ana—El Salvador’s tallest volcano. Unlike Coatepeque, Santa Ana remains active, with small to moderate explosive eruptions recorded since the 16th century. Its most recent severe eruption occurred in 2005.
Although the lake appears its usual blue in this photo, it can occasionally take on a strikingly different hue. At times, the water temporarily shifts to bright turquoise, prompting questions about its cause. In 2024, scientists reported that while pigments from microalgae and cyanobacteria can affect the lake’s color, the turquoise episodes are likely the result of natural mineralization.
The broader landscape around the lake and Santa Ana Volcano is a mos …