The National Oceanic and Atmospheric Administration says its mapping ship Fairweather found rocky areas less than 30 feet deep near Dutch Harbor in the Aleutian Islands.
NOAA says the areas were not detected by the last survey in 1935.
Dutch Harbor is a staging area for Shell vessels heading to the Chukchi Sea.
The 380-foot Fennica 10 days ago was departing Dutch Harbor when it was gashed by an obstruction that created a hole in its hull about 3 feet long and a half-inch wide.
Shell will send the icebreaker to Portland, Oregon, for repairs but does not expect an interruption in its drilling schedule.