Clouds encircle the lofty rim of Mount Elgon, a huge, long-extinct volcano on the border between Uganda and Kenya, viewed in this enhanced satellite image. The solitary volcano has one of the world's largest intact calderas, a cauldron-like central depression. The caldera is about 6.5 km (4 mi) across and formed following an eruption, when the emptied magma chamber collapsed under the weight of volcanic rock above it. For active volcanoes in Uganda, see the Natural hazards-volcanism subfield in the Geography section. Image courtesy of USGS.