The snow cap of Mount Kilimanjaro, famed in literature and beloved by tourists, first formed some 11,000 years ago, but will be gone in two decades, according to researchers who say the ice fields on Africa's highest mountain shrank by 80 percent in the past century.

Lonnie G. Thompson of Ohio State University said measurements using ice corings and modern navigation satellites show that the oldest ice layers on the famed mountain were deposited during an extremely wet period starting about 11,700 years ago.

The mountain is enshrined in literature, most notably Ernest Hemingway's "The Snows of Kilimanjaro" and some ancient beliefs in Africa hold the mountain to be a sacred place.

But a temperature rise in recent years is eroding the 150-foot-high blocks of ice that gave Kilimanjaro its distinctive white cap.

"The ice will be gone by about 2020," said Thompson. The diminishing ice already has reduced the amount of water in some Tanzanian rivers and the government fears that when Kilimanjaro is bald of snow the tourists will stop coming.

"Kilimanjaro is the number one foreign currency earner for the government of Tanzania," said Thompson. "It has its own international airport and some 20,000 tourists every year. The question is how many will come if there are no ice fields on the mountain."

Africa was not alone in the global drought. Thompson said other records show that civilizations during this period collapsed in India, the Middle East and South America.

Researchers put markers atop the ice field blocks in 1962 and Thompson said measurements using satellites show the summit of the ice has been lowered by about 56 feet in 40 years. The margin of the ice also has retreated more than six feet in the past two years.

"That's more than two meter's worth of ice lost from a wall 164 feet (50 meters) high," said Thompson. "That's an enormous amount of ice."