A mapping expedition in which an explorer broke a leg deep below the Earth's surface discovered 2.6 more miles to Lechuguilla Cave, making it the eighth-longest in the world, authorities say.

At 56.9 miles, the cave jumped four notches from 12th in the world, Carlsbad National Park management assistant Bob Crisman said Sunday.The cave is the deepest in the United States at 1,565 feet and is the fourth-longest in the country.

The latest discovery was made during an expedition in which Emily Mobley of Schoharie, N.Y., broke a leg and had to be rescued. After the rescue, the expedition resumed April 4, discovering 2.6 more miles of rooms and passages.

The longest cave in the United States, Kentucky's Mammoth Cave, has more than 330 miles of explored passageways.