REPEAT-Huge ice island calves off Greenland glacier

(Refiles to correct spelling of Strait in second paragraph)

* Largest such event in the Arctic in 50 years

* Island could break up, fuse to land, or drift south

WASHINGTON, Aug 6 (Reuters) - An ice island four times the size of Manhattan broke off from one of Greenland's two main glaciers, scientists said on Friday, in the biggest such event in the Arctic in nearly 50 years.

The new ice island, which broke off on Thursday, will enter a remote place called the Nares Strait, about 620 miles (1,000 km) south of the North Pole between Greenland and Canada.

The ice island has an area of 100 square miles (260 square km) and a thickness up to half the height of the Empire State Building, said Andreas Muenchow, professor of ocean science and engineering at the University of Delaware.

Muenchow said he had expected an ice chunk to break off from the Petermann Glacier, one of the two largest remaining ones in Greenland, because it had been growing in size for seven or eight years. But he did not expect it to be so large.

"The freshwater stored in this ice island could keep the Delaware or Hudson Rivers flowing for more than two years," said Muenchow, whose research in the area is supported by the National Science Foundation.

"It could also keep all U.S. public tap water flowing for 120 days."