10 Incredible Holes

Grand Canyon
The Grand Canyon is one of the world's greatest natural wonders. iStock/Thinkstock

The word "hole" seems like an overly simplistic term to use when describing the Grand Canyon, one of nature's most stunning geologic features. Located in northern Arizona, United States, the magnificent gorge is a vibrant display of reds, oranges and yellows; it was visited by nearly 4.5 million tourists in 2009. The Colorado River, which roars through the canyon bottom at an elevation gradient of 7 feet per mile (1.3 meters per kilometer), is responsible for carving the canyon over the last 6 million years and exposing rock at the bottom that is nearly two billion years old. One of the world's most famous geologic features, the Grand Canyon was designated a national park on Feb. 26, 1919, and a United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site in 1979.

While its beauty is well-known, the sheer size of the Grand Canyon is enough to qualify it as an incredible hole. Along its 277-mile (446-kilometer) length the Canyon boasts an average width of 10 miles (16 kilometers) and an average depth of one mile (1.6 kilometers). Interestingly, the elevation difference between the rim and the canyon floor is responsible for a significant temperature difference; the average high temperature at the bottom is 82 degrees Fahrenheit (28 degrees Celsius), while the average temperature at the South Rim is 63 degrees Fahrenheit (17 degrees Celsius).With such impressive dimensions, it isn't surprising that the Canyon's total volume is an unfathomable 5.45 trillion cubic yards (4.17 trillion cubic meters) [source: National Park Service].