Caption: Crossing of the Red Sea, painting by Nicolas Poussin (1634).
The sun sank over the eastern Nile Delta. A man stood on the shore of a great sea of reeds. As twilight fell upon the land of Egypt, he raised his rod. A howling wind blew from the east all that night, and in the morning the man beheld a strange and marvelous sight! The sea was completely gone, blown away to the west, and people could walk upon the dry ground where only yesterday fish swam and boats sailed. The man was astounded at this marvelous display of the power of wind over water.
This man's name was not Moses, but Major-General Sir Alexander B. Tulloch. He served in the British army in 1882, not in the Hebrew army of 1250 B.C. And the rod he raised was a surveyor's rod, not a prophet's staff. Nevertheless, Tulloch recognized the similarity between the event he witnessed and the narrative in the biblical book of Exodus 14. Tulloch wrote in 1896:
One day, when so employed [surveying] between Port Said and Kantarah, a gale of wind from the eastward set in and became so strong that I had to cease work. Next morning on going out I found that Lake Menzaleh, which is situated on the west side of the [Suez] Canal, had totally disappeared, the effect of the high wind on the shallow water having actually driven it away beyond the horizon, and the natives were walking about on the mud where the day before the fishing-boats, now aground, had been floating. When noticing this extraordinary dynamical effect of wind on shallow water, it suddenly flashed across my mind that I was witnessing a similar event to what had taken place between three and four thousand years ago, at the time of the passage of the so-called Red Sea by the Israelites.
The phenomenon that Tulloch witnessed is known to meteorology and oceanography as wind setdown. When strong winds blow over water for an extended period of time, the entire body of water shifts downwind and acquires a low-angle tilt within the enclosing basin. The water level at the upwind shore drops and is termed the “wind setdown.” The water level at the downwind shore rises and is familiar to hurricane watchers as a “storm surge.” Wind setdown is opposite in vertical direction and comparable in magnitude to storm surge, although wind setdown is less well known because it usually poses no danger to lives and property. Wind setdown events on the order of 2 meters are recorded every few years by NOAA measuring stations at the western end of Lake Erie. NOAA found that Cedar Key Harbor in Florida experienced a 1.0-meter drop in water level on September 6, 2004, as Hurricane Frances passed through, then rose to 1.5 meters above sea level 9 hours later.
Researchers use the Regional Ocean Modeling System (ROMS) to simulate wind setdown and storm surge. The “extraordinary dynamical effect” reported by Tulloch can be demonstrated on a computer by creating a digital lake and applying wind stress. Lake Manzala today is about 45 kilometers long, and Tulloch reported a depth near Port Said of 5 to 6 feet. Using ROMS, the researchers created a digital lake that is a rectangle 45 kilometers long and 6 feet deep (1.83 meters). Because Tulloch did not report the wind speed accurately, researchers selected a speed of 28 meters per second (100 km/h) to represent a medium-strength tropical storm on the Saffir-Simpson scale. A 100-km/h wind would be memorable but would not prevent Tulloch from walking. After 12 hours of wind at 28 meters per second, there appears a dry area of exposed lake bottom on the upwind side 11 kilometers long, with a corresponding storm surge on the downwind shore (Figure 1). One can imagine people walking across the mud flats where about 2 meters of water once stood. Tulloch reported that the water's edge had receded 7 miles (11.3 kilometers) from the Suez Canal.
Figure 1. Wind setdown and storm surge. In this idealized flat lake, wind blowing from the east (right) at 28 m/s pushes the water mass toward the western shore, leaving an area of exposed lake bed on the upwind side. The vertical scale here is greatly exaggerated. The human figure is 6 feet tall. Black arrows show the circulation within the lake. The red dotted line represents the original water level.
Dividing the Waters
If it is meteorologically possible for wind setdown to dramatically empty a body of water, it appears there could be more to the biblical parting of the Red Sea than many might assume. Exodus 14 contains the famous account of Moses crossing the Red Sea. Verses 21 and 22 state: “Then Moses stretched out his hand over the sea, and all that night the Lord drove the sea back with a strong east wind and turned it into dry land. The waters were divided, and the Israelites went through the sea on dry ground, with a wall of water on their right and on their left.” The author of Exodus ascribes the Israelites' deliverance to the Hebrew God, but there are enough natural components in the story to permit study using the tools of modern science. In particular, the Exodus narrative contains a detail not present in the Tulloch account: Water was present on both sides of the crossing. Is there a scientific basis for the reported event? Can wind stress really cause a body of water to separate and form a temporarily dry land bridge?
Researchers Doron Nof and Nathan Paldor suggested in 1992 that a shallow reef near Suez became exposed during a wind setdown, but the ROMS computer simulation indicates that it is unlikely that such a scenario could have occurred in one night. Unless such a reef is of uniform depth, the ocean model shows knee-deep rivers of seawater flowing through any low spots even after 12 hours. An alternate possibility is that the described body of water might contain an angled bend, as illustrated in Figure 2. Under wind stress the water mass would shift downwind and divide at the point of the bend, leaving an area of exposed mud flats for the crossing. If the wind abruptly stopped or changed direction, the waters would suddenly return and overwhelm anyone trapped in the passage.
Figure 2. Division of waters at an angled bend. Green represents land surface, blue and white represent water, and brown represents exposed lake bottom.
A likely place to look for such an angular bend is in the eastern Nile Delta, an area of shallow lagoons, shifting river channels, and reedy marshes. The Hebrew term for “Red Sea” is yam suf, which can also be translated “Sea of Reeds.” The construction of the Suez Canal during the 1860s drastically altered the eastern Delta, and modern scientific sources do not agree on the exact geography of this region in 1250 B.C. Nevertheless, a map drawn by James Rennell in 1830, based on the writings of Herodotus, has some contemporary support from archaeologists and geologists. Rennell showed an angular bend occurring at the confluence of the Pelusiac branch of the Nile and a large coastal lagoon then known as the Lake of Tanis, as shown in Figure 3. Under an easterly gale the wind setdown should begin at Pelusium, spread westward, and divide the waters around the eastern end of the province of Sethrum.
Figure 3. Confluence of the Pelusiac branch of the Nile river with the Lake of Tanis at Pelusium (detail of Rennell map).
“Then Moses stretched out his hand over the sea, and all that night the Lord drove the sea back with a strong east wind and turned it into dryland.”
To test the Tanis hypothesis, a computer simulation must reflect the likely geography of the eastern Nile Delta during the New Kingdom period, including the probable routes of extinct river channels and ancient lagoons. Assume a water depth of 2 meters (based on the present average depth of Lake Manzala, 1.3 meters)—which is the depth reported by Tulloch, 5 to 6 feet—and accounts from Herodotus that describe traveling by ship along the Nile branches. Assuming also a 28-meter-per-second wind speed, the ROMS computer simulation produces an area of dry ground between the eastern tip of the Sethrum peninsula and a bluff later known as Tell Kedua about 3 kilometers to the east, as shown in Figure 4. This area—known as the Kedua Gap—becomes dry to about 5 kilometers wide as measured from north to south, and the passage remains open for 4 hours.
Figure 4. ROMS model results for the Kedua Gap at 13:00 hours, during the closing phase one hour after the wind stops. Elevation and depth are in meters.
What About Moses?
Is there any indication in the Exodus account that Moses and company might have been standing hopefully at the eastern tip of Sethrum on a windy night in 1250 B.C? Or is the Tanis model merely a hydrological curiosity? Exodus 14:1–2 contains specific directions: “Then the Lord said to Moses, ‘Tell the Israelites to turn back and encamp near Pi Hahiroth, between Migdol and the sea. They are to encamp by the sea, directly opposite Baal Zephon.’” Archaeologist and biblical scholar James Hoffmeier places Migdol of Egypt's New Kingdom period near Magdolum as shown on the Rennell map. Pi-hahiroth is thought to mean “mouth of the canal(s).” The Pelusiac branch of the Nile was used in ancient times as a canal for transportation and irrigation, as were smaller channels passing near Migdol itself. If the land bridge at Kedua correlates with the Exodus narrative, then Pi Hahiroth is at the eastern tip of Sethrum, where the Pelusiac branch empties into the Lake of Tanis. While certainty cannot be achieved here, there is at least some similarity between ancient place names and the selected site. Several Bible atlases show a “traditional route” of the Exodus passing through the northern Isthmus of Suez.
Figure 5 shows a satellite view of the Kedua Gap today. Modern vegetation patterns still mark the outlines of those ancient bodies of water. From Pelusium a sandstone ridge known as the Pelusium Line runs southwest, dividing the ancient Tanis lagoon from a smaller paleolagoon at Migdol. Irrigation canals traverse the Kedua Gap, bringing water to the eastern Nile Delta. Roman ruins at Pelusium glow under the Egyptian sun. Archaeologists dig at Hebua, hoping to recover more remains of the Pharaonic empire.
Figure 5. Satellite photo of the Kedua Gap today.
Is it possible that the Red Sea story represents another chapter in the annals of weather's great impact at key points of human history? Did a prophet named Moses once stretch out his hand from Pi Hahiroth over the Lake of Tanis? Did wind setdown provide a safe passage over to Tell Kedua on some fateful night? Were Pharaoh's horses and officers crushed here under a thundering wall of water?
Ocean modeling can tell us only so much. The Exodus 14 narrative matches a known meteorological phenomenon, but other disciplines must also weigh in on the problem. Additional cores of sediment must be drilled and analyzed. Egyptology, archaeology, anthropology, geology, textual analysis, oceanography, linguistics, hydrology, refugee movement, and military science can all contribute their expertise. A firm conclusion may prove elusive. But while scientists debate and computer models run, the dramatic story of that night at Pi Hahiroth will remain a fascinating study.
“The Exodus 14 narrative matches a known meteorological phenomenon, but other disciplines must also weigh in on the problem.”
CARL DREWS works as a Software Engineer at the NCAR Earth System Laboratory in Boulder, Colorado. This article describes his master's thesis research at the University of Colorado. NCAR is sponsored by the National Science Foundation.