A team of U.S. geoscientists thinks they may have discovered the reason that the Colorado Plateau suddenly surged above the surrounding region millions of years ago.

The cause? A giant underground "blob" deep beneath the Earth's crust that scientists call a "lithospheric drip."

In a region defined by its magnificent geology, the formation of the Colorado Plateau and subsequent carving of the Grand Canyon have posed a longstanding problem for geoscientists. Typically when a region rises so dramatically in elevation, major deformations like mountains dominate the landscape. Instead, the topography of the 130,000 square-mile region is mainly flat, taking its shape from the slow forces of wind and water. In their research, which was published by the journal Nature on Wednesday, the team describes how they found a cold, dense area 120 miles beneath the Grand Canyon that was sinking deeper into the Earth. They say that the region chunked off pieces of the Earth's crust above it as it sank, and allowed another, much more buoyant layer to rise up and fill the chunked off space.

The researchers believe the sinking of this colder region and subsequent uplift happened as recently as 7 million years ago and is likely only one of many events that forced the plateau upwards.

Because erosion is largely driven by elevation, the rising surface would also have had an impact on shaping the Grand Canyon -- scientists say that erosion rates at the canyon dramatically increased 6 million years ago.

Similar drips have recently been discovered in the Sierra Nevada of California, the Wallowa Mountains of Oregon and Nevada's central Great Basin.

Two schools of thought dominate the geologic theories of the canyon. One says that the canyon formed 7 million years ago and another, more controversial theory says that large parts of the canyon were almost as deep as they are now 20 million to 60 million years ago. The research published Wednesday favors a very young Grand Canyon.

Writing a scientific editorial on the new find also in Nature, University of Arizona geologists George Zandt and Peter Reiners described the research as convincing, but said the Grand Canyon could still be older.

"It is likely that the story of one of geologists' favorite natural laboratories and playgrounds is far from fully told," the pair said.

Eric Betz can be reached at ebetz@azdailysun.com or 556-2250.

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