The biblical story of the 10 Plagues of Egypt is central to the origin of the Passover holiday, which commemorates the emancipation of the Israelites from slavery in ancient Egypt. As described in the Book of Exodus, the plagues were a succession of apocalyptic calamities exacted upon ancient Egypt as divine punishments for an unnamed pharaoh’s refusal to free the Israelites from captivity.

While little archaeological and historical evidence exists to corroborate the biblical accounts of the plagues, the existence of Moses or the mass exodus of the Israelites, scientists theorize that a chain reaction of natural phenomena could explain the seemingly supernatural catastrophes portrayed in the Bible.

“From an historical standpoint, the first nine plagues resemble natural events well known in the Middle East, save for their patterns and rapid succession,” reported a 2008 study in the Yale Journal of Biology and Medicine.

What Are the 10 Plagues of Egypt?

The Ten Plagues of Egypt, as described in the Book of Exodus include, in order of their unleashing: 1. water turning to blood 2. frogs 3. lice 4. flies 5. livestock pestilence 6. boils 7. hail 8. locusts 9. darkness and 10. the killing of firstborn children.

Epic Drought Could Have Caused Plagues

Archaeological excavations suggest that the ancient Egyptian capital of Pi-Ramses was abruptly abandoned during the reign of Pharaoh Ramses II (between 1279 B.C. and 1213 B.C.), believed by some scholars to be the Egyptian king depicted in the Book of Exodus.

Studies of stalagmites in Egyptian caves have found that timing coincides with a period of prolonged drought. AccuWeather founder and executive chairman Dr. Joel N. Myers, author of Invisible Iceberg: When Climate and Weather Shaped History, says the extended dry spell could have triggered a domino effect of natural disasters such as those described in the Bible.

“Once you have a drought and a heat wave, everything changes,” he says. “When the climate changes, a series of disruptions occur that feed on each other.”

Climatologists suggest that a severe drought that upset the delicate ecological balance of the Nile River delta could explain the first biblical plague in which Moses and his brother Aaron turned Egypt’s waterways to blood. According to biologist Stephan Pflugmacher, the arid weather would have produced ideal conditions for microscopic “Burgundy Blood” algae to blossom in the Nile’s slow-moving, warm waters. The toxic freshwater algae could have killed off fish populations and turned Egypt’s rivers a blood-red color.

The algae bloom could have starved the Nile River of oxygen, unleashing a series of reactions matching the five subsequent plagues of frogs, lice, flies, livestock pestilence and boils on beast and people. Deprived of oxygen and fish, frogs would have fled their natural habitat and overrun Egyptian homes where they died.

The demise of their natural predators would cause insect populations to proliferate. A 1996 study by Curtis Malloy and epidemiologist John Marr theorized that the lice described in the Bible were actually culicoides, insects whose larvae feed on decomposing animals such as fish and frogs and are known to transmit fatal infections to cattle, horses and sheep.

Since culicoides cannot fly well, they may not have reached the Israelite land of Goshen, leaving the Hebrews unaffected. Malloy and Marr surmised that tainted meat and flies could have spread glanders, a highly contagious bacterial disease that is known to cause boils on humans and animals.

Myers says the drought could also be tied to the eighth plague—locusts. Forced into the few remaining areas of vegetation by the dry weather, the overcrowded locusts may have reproduced at a rapid rate when the rains returned, and the resulting swarms would have devoured Egyptian crops.

“We’ve seen similar documented examples in the Middle East, and the United States in the 1800s saw the damage locusts could do,” says Myers, who notes that a one square kilometer locust swarm can eat as much food in a day as 35,000 people.

The Volcanic Eruption Theory

While proponents of the drought theory connect the seventh and ninth plagues—fiery hailstorms and days of darkness—to an unrelated sandstorm, some scientists believe they may have been caused by a volcanic eruption on the Greek island of Santorini. Although the eruption occurred more than 500 miles away, pumice from Santorini has been found near the site of Pi-Ramses.

The billions of tons of volcanic ash that spewed from one of history’s most powerful eruptions could have triggered violent thunderstorms, blacked out the sun for days and produced wet, humid conditions favorable for locust reproduction. Volcano theory advocates also claim that acid in the volcanic ash, including cinnabar, could have turned the Nile River a toxic red and sparked a similar chain reaction as posited by the drought theory.

The eruption at Santorini is estimated to have occurred around 1620 B.C., some 400 years before the rule of Ramses II. However, the biblical account of the plagues, which were written hundreds of years after the events described and not intended to be an historical record, could have combined various natural disasters spanning centuries.

The Final Plague

The 10th and final plague in the Book of Exodus is the death of Egyptian firstborn sons. Myers theorizes that the locust-induced famine could have caused Egyptians to sacrifice their firstborn in a desperate bid to appease the gods.

Another theory holds that the series of plagues damaged crops and permitted a lethal mold to poison grain supplies. In Egyptian society, the firstborn sons would have been given the first opportunity to eat—and would have been the first to succumb from the contaminated top layers stored in the granaries.

According to the Bible, the pharaoh granted the Israelites their freedom after the 10th plague claimed the life of his firstborn son. When the pharaoh changed his mind and ordered his army to go in pursuit, the Israelites made a miraculous escape when Moses parted the Red Sea.

Scholars theorize that the Israelites didn’t cross the present-day Red Sea, but a series of shallow lakes known as the “Sea of Reeds” that once existed where the Suez Canal is now located. While a drought could have dried out the swamp and allowed the Israelites to pass, another theory holds that strong winds of more than 60 miles per hour could have pushed the lake water and created a temporary land bridge that could have been crossed on foot but closed by the time the pharaoh’s chariots arrived.

“The probability is low, but I could imagine there was some type of wind that caused a seiche [standing wave] that occurs in lakes,” Myers says. “It may not have been as dramatic as in the movie The Ten Commandments, but the weather impact could have caused almost a parting and then a closing.”

HISTORY Vault: Ancient Mysteries

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