Posted on 04/03/2009 1:11:37 PM PDT by decimon
More than 80 undersea volcanoes and a multitude of islands are dotted along the Hawaii-Emperor seamount chain like pearls on a necklace. A sharp bend in the middle is the only blemish. The long-standing explanation for this distinctive feature was a change in direction of the Pacific oceanic plate in its migration over a stationary hotspot – an apparently unmoving volcano deep within the earth. According to the results of an international research group, of which LMU Munich geophysicist Professor Hans-Peter Bunge was a member, however, the hotspot responsible for the Hawaii-Emperor seamount chain was not fixed. Rather it had been drifting quite distinctly southward. Nearly 50 million years ago, it finally came to rest while the Pacific plate steadily pushed on, the combination of which resulted in the prominent bend. The movements of hotspots are determined by circulations in the earth’s mantel. “These processes are not of mere academic interest,” Bunge emphasizes. “Mantel circulation models help us understand the forces that act on tectonic plates. This in turn is essential for estimating the magnitude and evolution of stresses on the largest tectonic fault lines, that is the sources of many major earthquakes.”
The characteristic bend in the trail of the 5000 kilometer long Hawaii-Emperor seamount chain is one of the most striking topographical features of the earth, and is an identifying feature in representations of the Pacific Ocean floor. For a long time, textbooks have explained the creation of the Hawaii-Emperor chain as an 80 million year-long migration of the Pacific oceanic plate over a stationary hotspot. Hotspots are volcanoes rooted deep within the bowels of the earth, from which hot material is constantly pushing its way up to the surface. According to this now obsolete scenario, the bend would have come about as the Pacific plate abruptly changed direction.
In the past 30 years, geophysicists had also depended on the apparently unchanging locations of hotspots in the earth's mantel in their definition of a global reference for plate tectonics. More recent investigations, however, suggest that hotspots are less stationary than so far assumed. An international research group, of which Professor Hans-Peter Bunge of the LMU Munich Department of Earth and Environmental Sciences was a member, took a closer look at certain evidence pointing towards substantial inherent motion of the underground volcanoes, and has now confirmed this evidence.
“Paleomagnetic observations suggest that the bend in the Hawaii-Emperor chain is not the result of a change in the relative motion of the Pacific plate,” Bunge states. “On the contrary, it seems the hotspot had been drifting rapidly in a southward direction between 80 and 40 million years ago before it came to a complete halt.” If the trail of the Hawaiian hotspot is corrected to include this drift, the result implies a largely constant movement of the Pacific plate over the last 80 million years. The bend ultimately came about as the hotspot started to slow down.
The driving force behind the migration of the hotspot is the circulation of material under the surface of our planet. “The earth’s interior is in constant motion,” reports Bunge. “Over geological timescales, this motion compares to the weather patterns in our atmosphere. These patterns can easily lead to a change in position of hotspots. Numerical simulations of this global circulation in the earth’s mantel allow us to retrace these motions in unprecedented detail.”
The new data will now be entered into the mantel circulation models presently used. These calculations help explain the driving and resisting forces acting on tectonic plates. “And we need to understand these forces because they are essential for estimating the magnitude and evolution of stresses on the major tectonic fault lines – that is, the sources of many major earthquakes on our planet,” says Bunge. The findings to come from these models will allow scientists to improve their computer models by checking their calculations against observations. (hp/suwe)
You will find more information about the calculations at: www.earthmodels.org/publications/science-2009
Publication: “The Bent Hawaiian-Emperor Hotspot Track: Inheriting the Mantle Wind”, John Tarduno, Hans-Peter Bunge, Norm Sleep, Ulrich Hansen, Science, 3 April 2009
Contact: Professor Hans-Peter Bunge Department of Earth and Environmental Sciences of LMU Munich Tel.: ++49 (0) 89 / 2180 – 4225 Fax: ++49 (0) 89 / 2180 - 4205 E-mail: hans-peter.bunge@geophysik.uni-muenchen.de Web: www.geophysik.uni-muenchen.de/Members/bunge
Bent bump ping.
Figure 1. Path of the Yellowstone hotspot. Yellow and orange ovals show volcanic centers where the hotspot produced one or more caldera eruptions- essentially "ancient Yellowstones"- during the time periods indicated. As North America drifted southwest over the hotspot, the volcanism progressed northeast, beginning in northern Nevada and southeast Oregon 16.5 million years ago and reaching Yellowstone National Park 2 million years ago. A bow-wave or parabola-shaped zone of mountains (browns and tans) and earthquakes (red dots) surrounds the low elevations (greens) of the seismically quiet Snake River Plain. The greater Yellowstone "geoecosystem" is outlined in blue. Faults are in black.
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Thanks decimon. |
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Seriously, there is a lot we are still discovering about geology and vulcanology even though this has been an actively studied field for more than a century. Also, if I recall correctly, meteorology and the study of climate change is also an area where we are still learning things. IN SPITE OF AL GORE'S "SETTLED SCIENCE"!
Hmm. Your dashed lines suggest volcano chains which are not parallel to the more recent Hawaiian trend. If the current Hawaiian trend is determined by plate motion alone, how is this possible? (Esp. since those other island trends seem more parallel to the older Hawaiian one, which the article attributes to migration of the hotspot)
Could also have something to do with the composition of the rock over the hotspot at any given time. Perhaps the rising magma follows the easiest course upwards, which may not always be the most direct route.
I’ve always wondered if it was the same hot spot responsible for the Siberian Traps, since the trail points in that general direction.
Uh-oh. That means Yellowstone is about to go boom.
Ah, you beat me to it.
I try not to go into Portland, OR too often, but when I do I am usually stuck in traffic, 4 lanes each direction. I think about all the pistons and valves (springs & valve guides included)going up & down, cams & alternators turning in each vehicle. I used to just keep track of the vehicles going in the opposite direction but recently added all those going in the same direction.
Is this motion of the Islands, plates, mantels & hotspots something I need to pay more attention to? I have space available.
Young-earthers will be deeply saddened.
Smile ... Depends on the state of your nerves and supply of "Depends(tm)" I guess. Portland is somewhat close to Mount Hood if I recall correctly and the USGS maintains an web page monitoring the condition of this active volcano. If it is important enough for local school kids to have volcano evacuation drills and active seismic monitoring - do you need to pay attention? Do you have the time to pay attention to everything that people tell you to worry about? I don't know about you, but I overloaded my worry file about 50 years ago and it is just getting worse all of the time!
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