The caldera of the Katla volcano has a diameter of and is covered with of ice. The volcano normally erupts every 40-80 years. The flood discharge at the peak of an eruption in 1755 has been estimated at 200,000-400,000 m3/s (7.1-14.1 million cu ft/sec), comparable to the combined average discharge of the Amazon, Mississippi, Nile, and Yangtze rivers (about 266,000 m3/s (9.4 million cu ft/sec)).