University of Rochester

Rochester Geophysicist to Lead Ocean Expedition to Track Earth's Roving Hot Spots

December 11, 2000

John Tarduno has spent four of the last five summers well above the Arctic Circle, camping out in tents for six weeks at a time, chasing down long-dead turtles and crocodile-like beasts. Next summer offers a change of pace. Instead of enduring snow and freezing rain, the University of Rochester geophysicist will lead an ocean cruise to the Pacific Ocean, tracking the geological feature that gave birth to the Hawaiian Islands.

Tarduno is one of two scientists chosen to lead a two-month expedition that will depart from Yokohama, Japan and trace a route along a series of seamounts and atolls created long ago by the same volcanic "hot spot" that more recently formed Hawaii. This week Tarduno and Robert Duncan of Oregon State University met to complete the planning for the voyage, selecting staff, choosing which areas to visit, and deciding which experiments to conduct. More than 100 scientists, engineers, and crew members from around the world will take part.

"Results of our project could wind up challenging some of the basic concepts about our planet that we teach everyday in the classroom," says Tarduno, professor of geophysics and chair of the Department of Earth and Environmental Sciences.

The entire mission revolves around some very fancy rock collecting. The team sets sail July 2, 2001 aboard the JOIDES Resolution, a deep-sea research vessel capable of retrieving some of the most remote rocks on the planet. The ship is equipped with a giant drill pipe that is lowered to the ocean floor, usually a mile or more below the water surface. Researchers will drill deep beneath the ocean floor, oftentimes a mile or so through sediment and rock, until they reach the rocks whose tales could offer answers to longstanding questions about the forces that shape the Earth and govern its future. The Resolution is powered by several thrusters tied to the Global Positioning System, so scientists will know, within a few feet, exactly where on Earth they obtained their samples.

While Earth has rocks aplenty, only the right rocks help scientists understand certain mysteries. That's part of the reason why the United States and 21 other nations come together to form the Joint Oceanographic Institutions for Deep-Earth Sampling (JOIDES), which sponsors the Ocean Drilling Program. It's a research effort devoted to gathering rock samples beneath the oceans, to further scientists' understanding of our planet.

A central question today concerns "hot spots," giant plumes of molten rock that pepper the planet and well up from deep within the Earth. The plumes can act like blowtorches that burn through the crust, creating chains of volcanoes or islands. The best known is the hot spot that created the Emperor Chain of islands (including Hawaii), atolls and seamounts; all are ancient volcanoes that rise from the ocean floor, but seamounts aren't tall enough to break the surface.

Tarduno and his team, including researcher Rory Cottrell, have found some of the best evidence yet that hot spots are actually on the move. Yet, many scientists still assume that hot spots are fixed in place, and that they form chains of islands only when a tectonic plate moves over them. While plates certainly move, Tarduno and Cottrell says that hot spots themselves move too. The scientific community is split, with some geophysicists believing that hot spots can travel, while others say that a phenomenon known as "true polar wander," which describes how the Earth can tilt and change the orientation of its magnetic field, could explain some of the hot-spot data.

So Tarduno proposed an expedition to settle the question--roving hot spots vs. true polar wander--and his proposal was rated the highest of approximately 100 proposals submitted to JOIDES. For two months Tarduno's team will pay visits to at least six seamounts in the Emperor Chain, spending about a week at each. At each site the ship will drill far beneath the ocean floor and eventually extract a core of rock about half a foot wide and anywhere from 300 to 1,000 feet long. Those rocks, which formed long ago from molten lava spewing forth from the innards of the Earth, will be brought on board, studied extensively during the cruise, and then divvied up among dozens of scientific teams for further analysis.

The team will depart from Japan and will head due north 1,500 miles, beginning their studies in Russian waters at a sea mount approximately 90 million years, the oldest geologic "cousin" of the Hawaiian Islands. From there they'll work their way south, far off the coast of Kamchatka, stopping at several seamounts along a 3,000-mile route; as they move south they'll move on to younger and younger seamounts, eventually studying one 48 million years old.

With rocks in hand, scientists will begin a battery of tests designed to discover the rocks' origin, putting in 12-hour days seven days a week for the length of the cruise. The most important measurement will be that of each rock's magnetic signature, which gives information about the "birthplace" of a rock, a bit like a person can be tagged as a native of New York City, or Georgia, or wherever, by his distinctive twang or unique accent. A rock is "born" when molten lava solidifies; a rock always carries the magnetic data of its birthplace, no matter where it ends up. At the University, Tarduno runs a sophisticated paleomagnetic laboratory, where he and Cottrell and their colleagues measure rocks' precise magnetic signatures. It's that measurement that tells scientists exactly where the hot spot that created that rock was at a given time in history.

If the hot spot is stationary, then the rocks from the seamounts should have been formed at the same latitude; they would have moved only because of plate tectonics or other forces. But if the hot spot is on the move, they would have been formed at different latitudes. Scientists will also make additional measurements to check for evidence of true polar wander during this period.

The work will do more than answer a single question about whether hot spots move. The findings could help scientists decide how much movement may be going on deep within the Earth, at the mantle, and it will help scientists understand the massive forces of convection that govern the behavior of our planet. The cruise will also give them a sense of Earth's enormity.

"It's a remarkable experience," says Tarduno, who has been on two previous expeditions. "When you sail for five or six days straight, and you're still a week away from any land, you truly experience that 70 percent of Earth is covered by water. Sometimes the water is smooth and at other times you see huge swells from some very distant storm. It's amazing."