Hawaiian-Emperor seamount chain

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Elevation of the Pacific seafloor, showing a long trail of underwater mountains stretching northwest from the Hawaiian islands

The Hawaiian-Emperor seamount chain is composed of the Hawaiian Ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, and the Emperor Seamounts, a vast underwater mountain region of islands and intervening seamounts, atolls, shallows, banks and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The seamount chain, containing over 80 identified undersea volcanoes, stretches over 3,600 miles from the Aleutian Trench in the far northwest Pacific to Lo‘ihi seamount, the youngest volcano in the chain, which lies about 35 km southeast of the Island of Hawai‘i. It is considered the largest mountain chain in the world. The Hawaiian Islands are that portion of the Hawaiian-Emperor seamount chain that projects above sea level.

In 1963, geologist John Tuzo Wilson hypothesized the origins of the Hawaiian-Emperor seamount chain explaining that they were created by a hotspot of volcanic activity that was essentially stationary as the Pacific tectonic plate drifted in a northwesterly direction, leaving a trail of increasingly eroded volcanic islands and seamounts in its wake. An otherwise inexplicable kink in the chain would mark a shift in the movement of the Pacific plate some 47 million years ago, from a northward to a more northwesterly direction, and the kink has been presented in geology texts as an example of how a tectonic plate can shift direction comparatively suddenly. A look at the USGS map on the Origin of the Hawaiian Islands clearly shows this "spearpoint". Recent research shows that the hot spot itself may be moving southward (Tarduno et al., 2003). More recent studies, mentioned below, provide evidence that the change in direction may have occurred over a period of about 8 million years.

Recent analysis of the magnetization orientation of cooling magnetite in ancient lava flows taken at four seamounts shows a more complex relationship than the textbook stationary hotspot offered. If the hot spot had remained above a fixed mantle plume during the past 80 million years, the latitude as determined by the orientation of the magnetite should be constant for each sample and should also signify original cooling at the same latitude as the current Big Island of Hawaii.

Yet more recently published argon-argon ages of rocks from volcanoes of the southern and central Emperor chain better establish the age at which the bend formed. Sharp and Clague (2006) determined that the bend initiated at about 50 million years ago, and the bending continued until about 42 million years ago. They also concluded that the bend formed because of the "traditional" reason -- a change in the direction of motion of the Pacific plate.

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Tarduno, John A., Robert A. Duncan, David W. Scholl, Rory D. Cottrell, Bernhard Steinberger, Thorvaldur Thordarson, Bryan C. Kerr, Clive R. Neal, Fred A. Frey, Masayuki Torii, and Claire Carvallo. 2003. The Emperor Seamounts: Southward Motion of the Hawaiian Hotspot Plume in Earth's Mantle. Science, July 24, 2003; 10.1126/science.1086442 (Science Express Research Articles).
Warren D. Sharp and David A. Clague, 50-Ma initiation of Hawaiian-Emperor bend records major change in Pacific Plate motion. Science, v. 313, p. 1281-1284 (2006).
Ken Rubin, "The Formation of the Hawaiian Islands"
USGS, "The long trail of the Hawaiian hotspot"
National Geographic News: John Roach, "Hot Spot That Spawned Hawaii Was on the Move, Study Finds": August 14, 2003
Warren D. Sharp and David A. Clague, 50-Ma initiation of Hawaiian-Emperor bend records major change in Pacific Plate motion. Science, v. 313, p. 1281-1284 (2006).