Scraping the bottom

From San Francisco, at a meeting of the American Geophysical Union

A survey of deep waters in western Lake Superior reveals the tracks left when massive icebergs scraped the lakebed during the last ice age.

Scientists have previously seen iceberg scours on the bottom of Lake Superior, but those were found in a shallow region near Wisconsin’s Apostle Islands. The newly discovered scrapes were detected with sediment-probing sonar in 200-meter-deep water far northeast of the islands, says Nigel J.