At the right spot – a sharp bend where a shallow river meets a coastal lagoon – and with the right contours of a waterway's bottom, wind moving across the bend could in effect push water both upstream and downstream, exposing the bottom. When the sustained winds finally die down, water returns from both directions to cover the muddy land bridge.
The phenomenon is known as wind setdown. Modeling results that the team conducted of a section of the eastern Nile Delta suggest that it could have had the right characteristics some 3,000 years ago to provide a temporary wind-swept land bridge for a group fleeing Egypt.
"The idea that these ancient stories and legends have a basis in scientific fact, that's what's really exciting," says Carl Drews, a software engineer at NCAR and lead author on the paper reporting these results. The paper appears in the online journal PLoS One, published by the Public Library of Science in San Francisco.
The work was part of a broader effort to use modeling to understand storm surges triggered by typhoons.
Wind setdown as a sea-parting mechanism in the region was initially proposed at least 18 years ago in research published in the Bulletin of the American Meteorological Society. But instead of looking at the eastern Nile Delta, the 1992 study involved wind setdown's effect on the northern tip of the Gulf of Suez, a slender arm of the Red Sea that rests between the Sinai Peninsula and the African continent.
Mr. Drews says he was drawn to look at the Nile Delta after reading an account of a wind setdown event in 1882 that affected part of a vast coastal lagoon named Lake Manzala, just west of the Suez Canal. Heavy, sustained winds blew from the east across the shallow lake, exposing some of the bottom.
"[T]he natives were walking around on the mud where a day before the fishing boats, now aground, had been floating," recounted Maj. Gen. Alexander Tulloch, who took part in Britain's invasion of Egypt that year. Tulloch presented his observations to the Victorian Institute and suggested a link to events in the Bible. The Victorian Institute was founded in 1865 to defend the Bible from what members saw as an assault on the biblical account of creation by the publication of Charles Darwin's "The Origin of Species."
Using satellite data and ancient maps of the region, Drews as well as Weiqing Han of the University of Colorado at Boulder estimated the lay of the land roughly 3,000 years ago and ran their model. Some researchers have suggested that a branch of the Nile would have flowed into the area, forming a U shape where it met the lake.
Drews and Dr. Han found that an east wind of 63 miles an hour, sustained for 12 hours, would clear a mud-flat path across the junction up to 2.5 miles long and some three miles wide. Anyone wanting to cross would have had about four hours to do it, according to the modeling results.
Some archaeologists and biblical scholars hold that the Israelites traveled through that area on their way east, Drews adds. The location selected for the study could have been the crossing point, Drews says.
He notes that a fortuitous blend of wind, water depth, and bottom contours could in principle lead to a temporary land bridge spanning a waterway. But, he adds, 3,000 years ago, sea levels would have been about 10 feet lower than they are today. That means there would have been no lagoon for a Nile tributary to reach.
Other researchers privately question whether the interpretation of the results isn't colored by wishful thinking from someone trying to find support in the physical sciences for events recounted in the Bible.
Drews and Han are careful in the paper itself to frame the work as an extension of previous studies, and its focus is on fluid dynamics. But Drews appears to draw biblical links more explicitly in the blog post "Crossing the Red Sea With Moses and Open Access."
"My Tanis [Lake Manzala] hypothesis suggests where and how Moses crossed the yam suf," he writes, referring to the Red Sea. "When remains a thorny issue."
Still, the results could feed into research into the origins of the biblical account in Exodus. The description of winds parting the waters "has a basis in physical laws," Drews says.