Icebergs Over Iowa

The Middle West is littered with deposits of rocky glacial debris, in widely scattered areas and apparently dating from widely separated eras. Most glaciologists account for them by a theory that the huge Pleistocene glacier advanced and retreated four times, dropping its deposits each time as it melted back. Last week Professor Richard J. Lougee of Clark University, Worcester, Mass., offered a new theory. At the Washington meeting of the American Association for the Advancement of Science, he argued that the glacier did not retreat, but stayed in place so long that its enormous weight pushed a giant dimple in the earth's crust. When the glacier finally began to recede, the dimple filled with water and became an inland sea.

According to Dr. Lougee's theory, the northern shore of this sea was a towering ice cliff. Great icebergs broke away and drifted toward the outlet, a wide estuary that led to the Gulf of Mexico. When they melted, their embedded stones dropped to the bottom, creating the many glacial deposits that have puzzled other glaciologists.

When the glacier finally drew back toward Canada (about 23,000 B.C.), the unburdened crust began to recover, and the dimple flattened out. Ohio, Iowa, Michigan and Wisconsin rose out of the Leverett Sea. The broad estuary that led to the Gulf shrank to form the modern Mississippi.

Even after the Mississippi settled into its modern bed, it remained and remains a geological curiosity. For, technically, it runs uphill. In a Department of Commerce publication, the U.S. Coast and Geodetic Survey reported that the headwaters of the Mississippi are 3,956.17 miles from the center of the earth, while its mouth on the Gulf of Mexico is 3,960.22 miles from the center. As the Mississippi flows from Minnesota to the Gulf, it climbs 4.05 miles farther from the earth's center.

The gimmick here, the Survey explains, is that the earth is not a sphere. The centrifugal force of its rotation makes it bulge outward at the equator. Since the oceans rotate with the earth, sea level follows the bulge. The Mississippi starts its journey 1,491 ft. above sea level at the latitudes of Minnesota. As it moves southward, its water feels more strongly the lifting effect of the earth's spin. Therefore, it can climb up the bulge, away from the earth's center. When it reaches the Gulf of Mexico, it meets the ocean, which has been raised to the same level by the same centrifugal force.

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