The molten rock just under Earth's solid crust sometimes erupts suddenly and violently, causing streams of red-hot lava and scorching high-speed avalanches called pyroclastic flows. Volcanoes can bury entire cities in ash, poison the air with suffocating gases, trigger earthquakes and tsunamis, and drastically alter our climate. Witness the world's most extreme volcanic disasters throughout history, from the Yellowstone supervolcano to Vesuvius and Krakatoa, and find out what could happen if they erupt again. Learn how volcanoes form, what causes them to erupt, and why the benefits may outweigh the dangers for the people who live near them. Discover the science and technology that could help volcanologists save lives by predicting future devastating explosions.