Did earthquakes spell doom for ancient Mississippian societies?

Mike Fitzgerald

Source - http://www.bnd.com/2015/01/25/3629103_did-earthquakes-spell-doom-for.html?rh=1

Steve Nagy

 It is a mystery that baffles the archaeologists who’ve spent decades excavating the remnants of the ancient American Indian societies that flourished along the Mississippi River for a thousand years in southwestern Illinois.

But then, suddenly, around the year 1400 A.D., those societies, including the large city that once covered the site of Cahokia Mounds State Historic Site, collapsed, sending their inhabitants fleeing from the region.

Why?

Archaeologist Gregory Vogel has a theory.

Vogel, during a lecture Sunday at the Cahokia historic site, said it’s likely a series of disasters, including war and drought, had plagued the region. But evidence indicates that a massive earthquake — one perhaps as powerful as the legendary earthquake of 1811 centered in New Madrid, Mo. — and its many powerful aftershocks made the area nearly impossible to live in for months or even years, resulting in the exodus that nearly emptied the area of humanity before the first Europeans arrived.

“That might’ve been kind of the last straw,” said Vogel, who teaches archaeology and anthropology at Southern Illinois University Edwardsville and whose lecture Sunday afternoon was entitled “The Archaeology of Disaster.”

Vogel traced the impact of prehistoric fires, floods and earthquakes that have shaped the region’s environment and history.

“The main point of it is, the better we understand how these things happened in the past, the better we’re able to predict how often they happen in the future,” Vogel said.

Vogel galvanized the attention of the 80 people on hand for Sunday’s lecture with his vivid descriptions of the impact of the great New Madrid earthquake of 1811 — the most powerful earthquake in recorded North American history, a natural disaster so devastating that it changed the course of the Mississippi River, knocked down log cabins many miles away and fouled the air with the stench of fire and brimstone for months.

“Thank goodness there were almost no people here,” Vogel said.

Trouble is, earthquakes as powerful as the New Madrid event happen about once every 500 years in this region. Geological evidence indicates that two such super-earthquakes happened twice in the past 1,200 years: the first some time between 800 and 1000 A.D., and the second between 1300 and 1600 A.D.

Vogel quoted studies that show that there is a 10-percent chance of another New Madrid-level quake, of a magnitude of up to 8 on the Richter Scale, happening within the next 50 years, while there is up to a 40-percent chance of a magnitude 6 quake happening in the same time span.

Bonnie Jackson, of Edwardsville, said she enjoyed Vogel’s lecture, but it did not frighten her. She acknowledged, however, that in 1990, she boosted her home insurance after a St. Louis University geologist made national headlines when he said there was a strong chance another New Madrid-level quake would hit the area late that year. It didn’t.

“It was kind of stupid, in retrospect,” Jackson said of her decision to boost her insurance.

Paul Chucalo, of Belleville, said he wasn’t frightened by the prospect of future floods and earthquakes. What worried him were tornadoes.

“That’s the big thing here,” Chucalo said. “They’re more immediate. They happen more often than the other things.”

The natural disasters that have always beset this region are being intensified by the impact of climate change caused by human activities, such as the burning of fossil fuels blamed for global warming, Vogel said.

“What climate scientists have shown is that the current environmental changes we’re experiencing increase the extremity of events,” he said. “So there are more droughts. There is also the potential for more floods and more concentrated rainfall events, to lead to greater floods than we’ve seen in the past.”