Welded tuff is significantly harder than other types of tuff and can be found in various locations around the world. Also known by the term ignimbrite, the rock covers vast expanses of land in Guatemala, New Zealand, Peru, and parts of the United States. One of the most famous occurrences of welded tuff can be seen at Yellowstone National Park in Wyoming. Created by a cataclysmic eruption more than 600,000 years ago, the huge welded tuff formation at the park is known as the Lava Creek Tuff.