Last year's Hurricane Ivan generated an ocean wave that towered higher than 90 feet at one point, says a study that suggests such giants might be more common than once thought.

Research indicates these are not "rogue waves but actually fairly common during hurricanes," said David Wang of the Naval Research Laboratory at Stennis Space Center, Miss.

The giant wave was detected 75 miles south of Gulfport, Miss., by instruments on the ocean floor that measure the pressure of water above them. Using those readings, scientists can calculate the height of waves from trough to crest.

Last Sept. 15, as Hurricane Ivan passed through the area, the instruments measured 146 large waves, including 24 higher than 50 feet and one at 91 feet, Wang and his colleagues report in today's issue of the journal Science.

The giant wave did not reach land. Unlike a tsunami, which reaches down to the sea floor, this was a wind wave, generated on the ocean surface by the powerful forces of the storm.

Hendrik Tolman, an ocean wave expert at the National Oceanic and Atmospheric Administration's Climate Prediction Center, said a wave such as the giant one measured during Ivan is within expected limits.

Ocean researchers generally focus on "significant wave height," which is the average of the highest one-third of waves, he said. Within that average, there can be much larger waves.

The highest significant wave height observed in Ivan was 52 feet as calculated by NOAA's buoys and 58 feet as calculated by Wang's group.