Volcanic eruptions aren't just violent; they're incredibly fast, often leaving people no time to flee. Here, a rescue worker walks among the dead in the white-gray ash of Argomulyo, a village in Indonesia. This eruption last November of Mt. Merapi, one of the most active volcanoes in the world, triggered a series of fast-moving pyroclastic flows, a combination of volcanic rock and gas that can reach temperatures of 1,000 degrees. This material barreled down Merapi's slopes at speeds of up to 100 miles an hour.