A long time ago, perhaps three thousand years ago, a massive storm hit the Georgia coast.
Georgia State Associate Professor of Geosciences Lawrence Kiage can see the evidence as he reviews a chart showing patterns of sediment deposited on the state’s barrier islands during past storms. The charts, which look like audio wave patterns turned sideways, point to a hurricane bigger than any living person – or his or her parents or grandparents – has seen in Georgia.
“It must have been a huge, huge, monstrous event,” Kiage says.
Kiage studies hurricanes by digging into the earth, taking soil samples and studying layers of sediment. His work is part of a relatively new science known as paleotempestology, the study of ancient storms.
By collecting and painstakingly studying sediment samples from islands along the Georgia coastline, Kiage hopes to uncover long-term storm patterns, and to predict when Georgia could get hit by a catastrophic hurricane.
“The question is, are we likely to have a repeat?” Kiage says. “Everybody says Georgia is very safe. Let’s find out. Is it really?”
Over the past century and a half, Georgia hasn’t seen many hurricanes, much less a catastrophic one in the league of Hurricane Katrina in 2005. The last hurricane to make a direct hit was Hurricane David in 1979, which made landfall as a weakened Category 1 on the Saffir-Simpson Scale.
Kiage says Georgia was hit by a couple of “intense” hurricanes in the 1800s, including at least one that likely would have been a major Category 4, if that terminology had been used at that time. But his mission is to look farther back, well before historical records, to document monster storms and try to understand their cycles.
“That information is important for emergency managers,” Kiage says. “They want to know, what is the best evacuation routes? How frequently are we likely to get these intense hurricanes? How much money should we invest in preparing for such extreme events?”
Clues Hidden Under the Sand
When a hurricane hits a coastline, it stirs up a storm surge that washes over land. It takes sand from the beaches with it, and microscopic organisms from the ocean, depositing them on adjacent marsh. Over the years, sediment has been deposited over the sand washed up by hurricanes.
“During the course of normal sedimentation, you’ll find a lot of peat there in the clay,” Kiage says. “So when we have a storm bringing in the sand, you’ll see a very immediate break in the natural deposition.”
The layers of sediment between the sand deposits can tell how active, or quiet, storms were during a given time period.
On Wassaw Island, for example, where Kiage did early work, he was able to sketch out a record of hurricanes stretching back nearly two millennia before present.
There, the record showed periods of increased activity from around 2,000 years ago to around 1,100 years ago, and then another active period from 100 years ago to the present.
The sand and sediment point to a quiet time between 1,100 years ago to 250 years ago.
To determine the time periods, Kiage is using different types of data, including remnants of vegetation, and even pollen, buried in the ground.
“If we can find something that represents vegetation, we can infer as to which climate was prevailing at the time,” he says.
The thickness of overwash layers can also tell scientists the strength of a given hurricane. Stronger hurricanes are accompanied by larger storm surges and will push more sand farther into adjacent marsh than weaker ones.
To get a better feeling for how overwash layers indicate hurricane strength, Kiage and his team have taken samples on Cumberland Island, Jekyll Island and St. Catherine’s Island. He says the samples from St. Catherine’s look especially promising and could give him insight into storm patterns going back more than 3,000 years.
Trying to Predict the Future
The National Oceanic and Atmospheric Administration (NOAA) predicts the 2013 hurricane season, which continues through November, will be “active to extremely active.” But NOAA doesn’t offer a prediction of how many big storms are likely to hit land this year.
And, for now, Kiage says he can’t either.
“No, no. That’s too short term,” he says, and laughs.
Kiage said there are a number of different hypotheses that attempt to explain the frequency of hurricanes, how strong they become, and the direction they take.
Some tie hurricane activity in the Atlantic Ocean to the El Niño climate pattern, a temporary change in the climate of the Pacific Ocean characterized by unusually warm ocean temperatures. Its opposite is called La Niña, where unusually cold ocean temperatures prevail.
Some researchers point to the position of the Bermuda-Azores High, a large persistent center of high pressure in the atmosphere that develops over part of the Atlantic Ocean.
Other scientists say solar activity can influence hurricanes.
Climate change appears to be another factor.
Kiage expects his soil samples to help inform the scientific debate.
Graduate students have worked with Kiage to take scrapings from the core samples collected from the coastal islands. The scrapings were put into thimble-sized bowls and heated in a kiln to temperatures as high as 1,832 degrees to determine the composition of soil and plant material in them.
Samples were also subjected to an X-ray fluorescence spectroscope, or XRF, to be bombarded with high-energy gamma radiation to detect what types of elements, such as iron, titanium, chlorine and sodium, are contained in the sand.
Those tests have helped Kiage paint a picture of the types of materials found at various depths in the core sample. Logging that data into a type of fever chart allows him to see patterns at a glance.
The next step is carbon dating and other techniques to identify more precisely when Georgia’s coast saw quiet years, and when the big storms came surging in.
Kiage expects to be ready to publish a paper this fall to share his findings, and he hopes his research will help Georgians and others in coastal communities have the data they need to know when the next major storm cycle may be coming.
“Nature writes a book for you,” Kiage says. “We’re here to decode what’s written.”