Yellowstone National Park is one of the great wonders of the geological world. Recent research has shown that the central lake at Yellowstone is indicative of a collapsed volcanic caldera caused by a huge eruption some 640,000 years ago. Yellowstone with its geysers, fumaroles, and hot springs is regarded as a 'super-volcano' and one of the most volcanic areas on earth, whose predicted eruption is now overdue. Lower Falls is a result of rapid lifting of the land by sub-volcanic action. The area was glaciated during the Ice Age and rapid meltwater has certainly assisted the erosion. The colours are hydrothermal in origin.