26. The Hyperactive Mount Kelut
Mount Kelut is one of the most active volcanoes on the island of Java, in today’s Indonesia. During the past millennium, it erupted more than 30 times. In just the 20th century, it went off four times, and its latest eruption occurred as recently as 2014. Throughout most of its history, Kelut had a massive crater, which filled with rainwater to form a beautiful lake.
The lake was an attractive vacation destination, but during eruptions, the lake’s waters frequently led to devastating mud flows, or lahars. In 2007, seeping lava piled into a big mound at the center of the crater, which displaced most of the lake’s water.