Hawaiian-Emperor seamount chain
|
|
The Hawaiian-Emperor seamount chain is composed of the Hawaiian Ridge, consisting of the islands of the Hawaiian chain northwest to Midway Island, 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 northeasterly 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 mya, 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. However, more 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 my, 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. A recent interpretation of the magnetization, that the hotspot itself also actually drifted southward between 81 and 47 million years ago, is causing geologists to rethink their model of the interior workings of the Earth (Roach 2003).
External link
- Ken Rubin, "The Formation of the Hawaiian Islands" (http://www.soest.hawaii.edu/GG/HCV/haw_formation.html)
- USGS, "The long trail of the Hawaiian hotspot" (http://pubs.usgs.gov/publications/text/Hawaiian.html)
- National Geographic News: John Roach, "Hot Spot That Spawned Hawaii Was on the Move, Study Finds" (http://news.nationalgeographic.com/news/2003/08/0814_030814_hotspot.html): August 14, 2003