The Maly Semiachik Volcano is a popular natural landmark often visited by tourists heading to the Valley of Geysers. Part of the Eastern Range, it rises 1560 meters above sea level. The name "Semiachik" comes from the Itelmen word "shemech," meaning "land of stones," later adapted into Russian. Maly Semiachik is a mountain ridge composed of three volcanic cones fused together. Once, this area was home to an ancient volcano called Stena, known for its high activity. Around 17,000 years ago, it underwent a series of powerful eruptions, leaving behind a large caldera approximately 15 km in diameter. The current cones differ in size and features. The northern cone is the oldest and highest. The central cone is dormant and partially buried. The southwestern cone contains several craters, including the Troitsky Crater, which houses a stunning acid lake with water in a gray-blue hue. The crater is named after volcanologist V. D. Troitsky, who first studied this natural phenomenon in the summer of 1946. The Green Lake in Semiachik’s Crater Tourists on helicopter tours can admire the panoramic view of the volcano and the turquoise lake. The lake, first observed by Troitsky's expedition, lies in a crater 300 meters deep and 800 meters wide. In 1946, its vivid green color inspired its name. The lake's acidic composition is constantly changing due to chemical reactions, which alter its water color. In the 1960s, the water turned turquoise, and by the 21st century, it became azure-gray. Although the water appears ordinary up close, its striking effect is visible only from a distance. The water is toxic, containing hydrochloric, sulfuric, and hydrofluoric acids. Only specially equipped experts can approach the lake. Its water level is gradually rising, with temperatures ranging from cool to as high as 40°C or even 70°C in certain moments. Descending to the lake requires climbing gear, as the crater walls, 200 meters tall, are steep and made of tuff and lava, with colorful striped patterns adding to their beauty. Eruptions of Maly Semiachik The Maly Semiachik Volcano has not erupted in recent times. Its last significant event occurred in the 16th century, forming the Troitsky Crater. Since then, the volcano has shown only minor activity, such as occasional gas emissions, most notably in 1945-46, which expanded the lake’s area. Maly Semiachik is a magnificent natural formation with a rich history, attracting visitors from all over the world.