Hills point to catastrophic ice age floods.

Hills point to catastrophic Ice Age floods

Fields of low hills that cover parts of inland Canada and the northern United States may seem quite distant from the watery world of Atlantis. Yet a Canadian geologist proposes these hills formed from huge Ice Age floods that sharply raised global sea levels and could have spawned myths of a swamped continent.

"There's nothing in recorded history that matches the size of these floods," says John Shaw of Queen's University in Kingston, Ontario, who has estimated the extent of the floods from the size of the ridges.

Called drumlins--a word derived from Old Irish -- these hills appear in concentrated fields in North America, Scandinavia, Britain and other areas once covered by ice. When seen from above, the aligned knolls sometimes look like a basket of eggs lying on their sides and pointing in the same direction. Some drumlins are made of sediments deposited onto bedrock; others are ridges carved out of the rock.

Most geologists believe drumlins developed gradually from the grinding action of heavy ice sheets as they moved over the land. But in the last several years, Shaw and others have proposed the controversial idea that floods of water flowing beneath the ice created many of the North American drumlins and possibly others around the world. They base this hypothesis on the shapes drumlins share with other land forms sculpted by meltwater.

According to Shaw, heat from the Earth formed huge lakes of meltwater that remained trapped beneath the North American ice sheet. As the sheet began to retreat near the end of the glacial age, the water broke through and flowed in torrents down to the Gulf of Mexico and Atlantic Ocean. While flowing under the ice cap, water would have surged in vast, turbulent sheets that sculpted and scoured drumlins. Each flood lasted until the weight of the ice cap once again shut off the outlet of the covered lake, Shaw says.

Through simple calculations described in the September GEOLOGY, Shaw estimates that 84,000 cubic kilometers of water must have discharged during the creation of one large drumlin field in northern Saskatchewan. Upon reaching the ocean, this flood would have raised global sea levels by 23 centimeters during a few days or weeks, he says.

In some ways, Shaw's hypothesis echoes ideas raised 14 years ago by a group of oceanographers who studied the ancient remains of one-celled animals buried under sediment on the floor of the Gulf of Mexico. The ratios of oxygen isotopes in these organisms suggested that sometime around 11,500 years ago, a large amount of freshwater entered the gulf, says Cesare Emiliani of the University of Miami in Coral Gables. On the basis of the isotope studies, Emiliani and his colleagues theorized that a sudden influx of meltwater from the ice sheet could have rapidly raised sea levels, sparking myths of a great deluge.

When Emiliani's group proposed the theory, glacial experts responded that the sun could not melt the ice sheet fast enough to create such a sea-level rise. Shaw's hypothesis relieves this problem by proposing that vast amounts of meltwater were stored under the ice.

Yet many other geologists contend the drumlin-flood connection doesn't hold water. "Several of us are strongly opposed to this idea," says John Menzies of Brock University in St. Catharines, Ontario.

Menzies says the ice sheet could not have remained stable if large sections of it rested on huge lakes instead of on rock. Moreover, he says, studies of rock under the ice in Antarctica show that moving ice can shape drumlins.