A thick plume of smoke can be seen in this photograph of the West Fork Complex fire, which was burning explosively in southwestern Colorado near Pagosa Springs. The image was captured on June 19, 2013, by astronauts aboard the International Space Station (ISS). The West Fork Complex was a combination of three fires: the West Fork fire, the Windy Pass fire, and the Papoose fire. Lightning ignited the first of the blazes on June 5, 2013, and together they had charred approximately 75,000 acres (30,000 hectares) by June 25. The fires were burning in rugged terrain with large amounts of beetle-killed spruce forests. The West Fork Complex fire was so hot that it spawned numerous pyrocumulus clouds -- tall, cauliflower-shaped clouds that billowed high above the surface. Pyrocumulus clouds are similar to cumulus clouds, but the heat that forces the air to rise (which leads to cooling and condensation of water vapor) comes from fire instead of sun-warmed ground. Scientists monitor pyrocumulus clouds closely because the clouds can inject smoke and pollutants high into the atmosphere. As pollutants are dispersed by wind, they can affect air quality over broad areas.