OREGON STATE UNIVERSITY

Study pins down size of Earth's largest mountain

05/14/2002

CORVALLIS, Ore. - A study at Oregon State University has made one of the most precise measurements yet of Mauna Loa on the island of Hawaii, which is recognized as the largest mountain in the world when considering the enormous volcanic mass that is included underneath the sea.

According to this analysis, which was done in conjunction with colleagues at the U.S. Geological Survey, the mountain comprises from 68,750 to 79,343 cubic kilometers, or 16,494 to 19,035 cubic miles. Of this, just a tiny portion extends above sea level. In the past, researchers believed the mountain had a volume of between 60,000 and 80,000 cubic kilometers, but the more detailed measurements in this study were made with the powerful tools of geographic information systems.

The research was presented today at the 98th annual meeting of the Cordilleran Section of the Geological Society of America.

The true volume of Mauna Loa is staggering when compared to other large mountains or volcanoes, experts say. For instance, it would take about 375 mountains the size of Mount Hood in Oregon, itself an 11,235-foot volcanic peak, to equal this gigantic volcano on the Big Island.

"Another thing that many people don't realize is that the mass of Mauna Loa is not just the amount that rises above the surrounding sea floor, but also includes a huge portion that's sunken beneath the sea floor," said Grant Kaye, a geology doctoral student at OSU who did this study. "Mauna Loa is so massive that it deforms the oceanic plate on which it sits and forms sort of an inverted cone which is almost as large below the sea floor as the portion that extends above it."

Mauna Loa, which extends 13,680 feet above sea level, has an enormous base that is more than 90 miles in diameter and extends about five and one-half miles up from the surrounding sea floor. The total distance from the peak of Mauna Loa to the inverted cone beneath the ocean floor appears to be about 10.56 miles. It's about one million years old, a youngster in geological time, and by far the biggest volcano on the newest of the Hawaiian Islands.

All of the Hawaiian Islands, and many others in a chain extending thousands of miles across the Pacific Ocean all the way to western Alaska, were formed when the mobile Pacific Plate moved across one of the Earth's major "hot spots" that has been in the same place for about 80 million years. These hot spots are believed to be plumes in the Earth's mantle, which begin to melt as they rise upwards, and punch through the overlying plate to form volcanic features.

The plate in this location is moving about four inches a year, approximately as fast as a person's fingernail grows, and over millions of years has left behind a string of volcanic islands as they are carried away from it in different locations.

Even now, the motion of the Pacific Plate is beginning to leave Mauna Loa behind and begin the creation of the next Hawaiian Island. Called Loihi, it is already rising up from the Pacific Ocean floor and one day will emerge above the sea.