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Hawaiian-Emperior seamount chain
Hawaii hotspot.jpg
Elevation of the Pacific seafloor, showing the Hawaiian-Emperior seamount chain stretching northwest from the Hawaiian Islands
Location North Pacific Ocean

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 5,800 kilometres (3,600 mi) from the Aleutian Trench in the far northwest Pacific to the Loʻihi seamount, the youngest volcano in the chain, which lies about 35 kilometres (22 mi) southeast of the Island of Hawaiʻi. 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".

More recent studies, mentioned below, provide evidence that the change in direction may have occurred over a period of about 8 million years. 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 from a "traditional" cause—a change in the direction of motion of the Pacific plate.

Recent research shows that the hotspot itself may have moved with time. Some evidence comes from analysis of the orientation of the ancient magnetic field preserved by magnetite in ancient lava flows sampled at four seamounts (Tarduno et al., 2003): this evidence from paleomagnetism shows a more complex relationship than the commonly accepted view of a stationary hotspot. If the hotspot had remained above a fixed mantle plume during the past 80 million years, the latitude as recorded by the orientation of the ancient magnetic field preserved by magnetite should be constant for each sample and should also signify original cooling at the same latitude as the current Big Island of Hawaii. Comparisons with the traces of other hotspots also test if the Hawaiian-Emperor bend records a change in plate motion. Tarduno et al. (2009) have summarized evidence that the bend in the seamount chain may be caused by circulation patterns in the flowing solid mantle (mantle "wind") rather than a change in plate motion.

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Coordinates: 32°06′04″N 173°50′52″E / 32.10111°N 173.84778°E / 32.10111; 173.84778

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