NOTES FROM THE JOIDES RESOLUTION ODP LEG 197: PURSUING PELE, GODDESS OF HAWAIIAN VOLCANOS

Anyone who has looked at a map of the floor Hotspots occur in many other places: Iceland, sure identical dips, all the same as that re- Aof the Pacific Ocean has been struck by the Yellowstone, and the Galapagos Islands are corded at Hawaii today. But, if we find other- remarkably linear chain of underwater moun- familiar examples. When people first com- wise it will mean that Pele has roamed. Early tains that trail west and then north from the pared the orientations and measured the ages results from measurements of these ancient Hawaiian Islands some 3000 miles. How did of volcanoes in different hotspot tracks, it ap- magnetic directions (called “paleomagnetics”) they get there? What do they tell us about the peared that the hotspots did not move much aboard the ship using an advanced supercon- deep inner workings of our planet? The an- with respect to one another. If this were true ducting magnetometer tell us that several vol- swers to these and other questions were the then the global array of hotspots would form canos formed well north of the present loca- mission of Ocean Drilling Program Leg 197. a very convenient means to measure plate mo- tion of Hawaii and tell us that the hotspot tions anywhere on the surface of the Earth — has moved south. And this means that all esti- According to legend, the goddess Pele lives each volcanic trail signals the direction while mates of plate motions based on hotspot trails within the island of Hawaii and has built the the rate at which volcanos age along the trail have to be adjusted for the movement of the volcanoes, one after the other, in a sequence. gives the velocity of the plate. Such a stable hotspots themselves, and our ideas about an The accepted scientific explanation for the ar- configuration of hotspots would also mean rangement of these giant volcanoes in a line, that the deep mantle is stagnant, and not much and their progressively increasing age away involved in plate motions. from the currently active island of Hawaii, is not too different: The floor of the ocean (the There is a very simple way to discover if Pele Pacific plate) is in slow but steady westward or any of her hotspot sisters have moved over motion across a focused, warmer-than-usual the lifetime of these volcanic chains. Lava, region of the underlying, more stationary in- when it cools, contains tiny magnetic particles terior (the mantle), called a “hotspot.” This is that act like compass needles that dip at the analogous to the trail of smoke carried away angle corresponding to the latitude of the vol- by a breeze across the top of a chimney. The cano. These are then “frozen” into place when Emperor Seamounts are the oldest, deepest the lava solidifies. Millions of years later, after and most northerly of these Hawaiian-built the volcano has drifted away from the hotspot volcanoes. They are named after the emper- with the moving plate, its lava flows still record ors of Japan. the precise dip of the magnetic particles ac- quired at the latitude of the hotspot. inactive deep mantle need to be The main objective of rethought. Scien- Leg 197 was to drill into tists will now re- several of the oldest vol- turn to their home canoes in the Hawaiian institutions to hotspot track, now far study the cores re- removed from Hawaii covered in much and sunk beneath the more detail. They ocean surface, to re- will probe more cover cores from an- of Pele’s secrets and report results over the cient lava flows. These next two years. will be measured to de- termine the latitude at For more information about Leg 197 or other which the lavas cooled. ODP Legs, please visit the ODP web site at: If the hotspot has not www.oceandrilling.org. moved we should mea-