Believed a “crazy” theory thirty years ago, a colossal mantle plume generating nearly as much geothermal energy as the Yellowstone supervolcano sits beneath Antarctica, NASA researchers announced this week, where they say its intense heat has contributed to melting and cleaving of sizable ice formations recently.
“I thought it was crazy,” recalled Hélène Seroussi of NASA’s Jet Propulsion Laboratory in Pasadena, California, of her reaction to the University of Colorado Denver scientist’s suggestion decades ago. “I didn’t see how we could have that amount of heat and still have ice on top of it.”
Despite Antarctica’s deceptively placid appearance, masses of ice remain in constant motion — slipping, smashing, and grinding against the continent, lubricated by an intricate system of rivers and lakes beneath the surface — the ease of which can act loosely as the barometer of an ice shelf’s health, the scientists say. As water drains from lakes and moves throughout the complex subsurface network, it forces the gargantuan ice above to rise and fall — occasionally, by as much as 20 feet.
“But in Marie Byrd Land, researchers found even more of that activity than the known regional heat sources could explain,” LiveScience reports. “Something else was cooking the ice shelf. About 30 years ago, researchers first began to suspect that a magma plume might be the cause, given the domed shape of the crust in that area.”
Seroussi and Erik Ivins, also of the Jet Propulsion Laboratory, created a numerical model with compiled melting and freezing information from ice sheets in the region, including natural sources of heat and its transport, friction, and other variables, to locate the theorized magma plume.
To ensure accuracy of the model, the researchers turned to NASA’s IceSat satellite for precise measurements of changes in altitude on the surface of the ice sheet — an imperative tool without probes under the ice.
“Their model confirmed the existence of a magma plume pumping about 150 milliwatts per square meter (or about 11 square feet) of heat up to the surface, and peaking at as much as 180 milliwatts per square meter in a region where a rift in the crust may exist. (A milliwatt is one-thousandth of a watt.) For comparison, a typical stretch of land in the United States gets about 40 to 60 milliwatts per square meter of geothermal heat, and Yellowstone gets about 200 milliwatts per square meter.”
Adds Forbes, “The Marie Byrd Land mantle plume appears to be the primary driver of volcanic activity in Antarctica.”
In the 1970s, mantle plumes were first proposed to explain the presence of hotspots — areas of heightened geothermal activity, such as the Hawai’ian Islands and headline-frequenting supervolcano of Yellowstone — located far from the boundaries of tectonic plates.
Mantle plumes, according to NASA, are “thought to be narrow streams of hot rock rising through Earth’s mantle and spreading out like a mushroom cap under the crust. The buoyancy of the material, some of it molten, causes the crust to bulge upward.”
Researchers note the mantle plume formed between 50 and 110 million years ago — well before the Western Antarctic ice sheet took hold — and, notably, is believed to have had substantial influence on planetary weather patterns.
“At the end of the last ice age around 11,000 years ago,” NASA’s statement observes in conclusion, “the ice sheet went through a period of rapid, sustained ice loss when changes in global weather patterns and rising sea levels pushed warm water closer to the ice sheet — just as is happening today.”
Titled, “Influence of a West Antarctic mantle plume on ice sheet basal conditions,” the study was published by the Journal of Geophysical Research: Solid Earth.
(Image Credits: NSF/Zina Deretsky)
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