My OperaA Hawaiian Hotspot Puzzle Solved
Wednesday, October 4, 2006 3:16:45 PM
New and more precise measurements have shown that the age of the Hawaiian-Emperor Bend is not 43 million years old as previously thought but around 50 million years.
So what? Why should we care? It is important to understand plate dynamics because they are a key source of earthquakes that form tsunamis in the Pacific.
What is this bend, and why is this old date important?
Over the past 80 million years volcano eruption and continued movement of the Pacific Plate over the stationary Hawaiian deep-seated hot-spot have left a long trail of (volcanic) seamounts and volcanoes across the Pacific Ocean floor. The resulting Hawaiian Ridge-Emperor Seamounts chain consists of at least 129 volcanoes and extends some 6,000 km from the Aleutian Trench off Alaska to the "Big Island" of Hawaii. It makes a bend with the Emperor Seamount Ridge as a first leg and the Hawaiian Ridge as the second leg. The bend is interpreted as a major change in the direction of Pacific plate motion – given that the (fixed) hot spot is thought to be stationary.
Radioisotopic ages for the islands and seamounts calculated in the 1960s to 1980s showed that the volcanoes of the chain become progressively older with distance from the currently active hot spot under Hawaii and thereby seemed to confirm the hot spot hypothesis. The age found for the Hawaiian-Emperor Bend (43 M y), however didn't fit with other evidence.
Improvements in isotopic dating techniques have allowed more precise dating of samples, and reevaluation of past results indicates that the ages of some samples reflected not the time of the original eruption but that of a later reheating event.
According to a publication in the Journal Science of 1 September 2006 the change of direction started around 50 million years ago and went on for several million years (completed after 8 million years). See also The Hawaiian- Emperor Bend: Older than expected in the same issue.
The age of the Hawaiian-Emperor Bend is critical to assessing its relation to other massive geological events on and around the Pacific plate. Events at about the same time:
The two latter tectonic events (leading to motion changes in the Eurasian or Australian plates) may have triggered the change of direction of the Pacific Plate.
If you don't have access to Science the story is well featured by The Honolulu Advertiser of 4 September at: http://www.honoluluadvertiser.com/apps/pbcs.dll/article?AID=/20060904/NEWS01/609050318/1190/NEWS
So what? Why should we care? It is important to understand plate dynamics because they are a key source of earthquakes that form tsunamis in the Pacific.
What is this bend, and why is this old date important?
Over the past 80 million years volcano eruption and continued movement of the Pacific Plate over the stationary Hawaiian deep-seated hot-spot have left a long trail of (volcanic) seamounts and volcanoes across the Pacific Ocean floor. The resulting Hawaiian Ridge-Emperor Seamounts chain consists of at least 129 volcanoes and extends some 6,000 km from the Aleutian Trench off Alaska to the "Big Island" of Hawaii. It makes a bend with the Emperor Seamount Ridge as a first leg and the Hawaiian Ridge as the second leg. The bend is interpreted as a major change in the direction of Pacific plate motion – given that the (fixed) hot spot is thought to be stationary. Radioisotopic ages for the islands and seamounts calculated in the 1960s to 1980s showed that the volcanoes of the chain become progressively older with distance from the currently active hot spot under Hawaii and thereby seemed to confirm the hot spot hypothesis. The age found for the Hawaiian-Emperor Bend (43 M y), however didn't fit with other evidence.
Improvements in isotopic dating techniques have allowed more precise dating of samples, and reevaluation of past results indicates that the ages of some samples reflected not the time of the original eruption but that of a later reheating event. According to a publication in the Journal Science of 1 September 2006 the change of direction started around 50 million years ago and went on for several million years (completed after 8 million years). See also The Hawaiian- Emperor Bend: Older than expected in the same issue.
The age of the Hawaiian-Emperor Bend is critical to assessing its relation to other massive geological events on and around the Pacific plate. Events at about the same time:
- A line of volcanoes in the western Pacific, called the Izu-Bonin-Mariana Arc started abruptly erupting just about 50 million years ago — at a time when the Pacific Plate began being pulled down and under the adjacent Australian Plate.
- Early Eocene initiation of the >2600-km Tonga-Kermadec arc in the southwestern Pacific may have contributed to redirection of Pacific plate motion. (See my Blog on Samoa Tsunami)
- The fast movement of the Indian plate was braked when it crashed into the Eurasian plate. (See my Blog on Kashmir, Himalaya and the Tibetan Plateau)
- The rifting of Australia from Antarctica, leading to convergence between the Australian and Pacific plates. (See my Blog on Antarctic Ice and Plate Tectonics)
The two latter tectonic events (leading to motion changes in the Eurasian or Australian plates) may have triggered the change of direction of the Pacific Plate.
If you don't have access to Science the story is well featured by The Honolulu Advertiser of 4 September at: http://www.honoluluadvertiser.com/apps/pbcs.dll/article?AID=/20060904/NEWS01/609050318/1190/NEWS
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