Plates Of The World
Original Image, and with other language options.
We will start with a ‘big picture’ that’s a bit simplified, then move in for a more detailed “close up” that is a bit more accurate. Don’t let that transition worry you…
If you look at that picture, you will notice that the North Island of Japan (Hokkaido) and about the top 1/3 of the South Island (Honshu) sit on the North American Plate (as does a nice chunk of Russia). In another posting, Pyromancer76 asked if Japan was being torqued due to the movement of Hokkaido 8 feet closer to the rest of North America? You can, IMHO, answer that by inspection of this diagram. Look closely and you can see little red arrows on the plate boundaries. This shows which way they are moving. Spreading, with the arrow heads pointed away from each other, or one plate being eaten by the other “Subducting” under it, when the arrows point at each other.
So we see for the whole top of the Pacific Plate that the arrows show subduction. The net force is pushing that “wedge” of the N.A. plate, upon which sits North Japan, toward the Pacific plate. But it tends to stick. So for long periods of time (100 year scale) it slowly gets pushed back and the land ‘bends’ a bit. Then, in a slipping thrusting movement, jumps a bit forward (and over) a bit of the Pacific plate. What that ought to mean is that for a long time northern Japan was slowly getting a bit bent away from the rest of N.America, and in the quake came back closer to ‘normal’.
There is an exception to this belief: Land deforms. Overtime, it deforms a lot. This is not a perfect process. So did it move 8 feet away, then spring 8 feet back, unbent? Very unlikely. The exact bendings and deformations are hard to know without measuring the land. But what we can say is that the subducting plate has some material come up again as the Volcanoes of Japan, making the land higher and wider over time, and that the pressure against that ‘wedge’ of the N.American plate with Japan on it will slowly bend and lift the land. North America and the Eurasian Plate are “locked” at the moment. There is a bit of mountains where they join, but not a lot. Most of the “impact” is being taken as subduction of the Pacific and volcano formation. So that’s where most of this last motion will show up. A “slow back”, then “fast forward” motion, a “springing” of Hokkaido and northern Honshu, with the ‘error’ or ‘delta’ of location showing up as mountains and the ‘excess’ from the subduction of the Pacific floor showing up as volcanoes.
(Yes, this is just the ‘big chunks’. If you look very closely you can find all kinds of detail that does not conform to this. Whole books can be written on the subtile “yes but”. I did NOT forget them, I have edited… Feel free to raise your favorite as a comment, if you like, then I won’t have folks complain that I made the posting too long by including it ;-)
OK, other “neat bits”.
Notice that we have arrows going up/down past each other near California. It looks like the Pacific Plate is sliding up toward Alaska (and that is how it is often presented here in the news. That “L.A. is sliding north and will someday be next to San Francisco”. But look at the bottom of the Pacific Plate. Being consumed from the SIDES but not the BOTTOM. The reality is that North America is moving southward more than that the Pacific plate is moving north. Golly, that’s a ‘bit different’… So it’s really that the Pacific Plate is ‘sitting still’ and getting swallowed up by the North American plate. (In very long time frames, the whole crust can wobble around, so we might all, net, end up rotating more northward. That’s a different question than the relative motions right now).
That the Filipino plate is shown as static is, IMHO, simplistic. There’s some action being ignored there… This page:
http://whatonearth.olehnielsen.dk/philippines.asp
has a nice write up of the complexities. Basically, it’s being consumed from both sides, but in a complicated way…
So the conclusion for Japan? Since the rest of Honshu is on the Eurasian plate, locked to the North American plate, and since that is also pressing forward (but with the Filipino and Pacific plates taking the motion) it ought to hold more or less the same relative position to the rest of Japan as long as the two major plates stay locked (and the Pacific subducting).
However… this is happening on the face of a sphere. As the N.A. / Eurasian plates move south, they need to ‘extend’. Something needs to be getting ‘longer’ here for the geometry to work.
Okhotsk By Gosh(k)
OK, that’s the ‘simple view’. But we can go into a bit more detail… That “wedge” of the “North American Plate” is being redefined by some folks. (I think they are likely correct, but we’re starting to get an awful lot of dinky plates being defined around the world and I’m suspecting, for some of them, some folks just needed a Ph.D. thesis or a new publication on the record …)
This article, for example, finds that the part of the Philippine plate near Japan is a ‘new plate’ and everthing will need to be rethought…
http://www.terradaily.com/news/tectonics-05zzb.html
But he’s already “Chief Researcher” so it must be true…
Okhotsk Plate
So here we can see that there is a chunk that is locked to the Eurasia plate at a piece that is now being redefined as the “Amurian Plate), but the top part is sliding just a bit (the “transform fault”) relative to the North American plate. IMHO, likely a chunk of the N.American plate that’s been busted off rather than bend or subduct under Eurasia. There is also a bit that is spreading (the red line) where it’s being pulled a bit away from the main part of the Eurasian Plate.
Doesn’t really change the analysis much, other than to note that there may be a bit of ‘mountain building’ at the “convergent boundary” in the middle of Honshu. I’d expect the Philippine plate to just keep on getting swallowed until the Pacific plate is directly subducting under the Eurasian/Amurian Plate with southern Japan on it, but things do sometimes change on this planet ;-)
And WHY is North America headed south
So, why is North America headed south? We know that the Atlantic is getting wider, and that can account for the spreading out and for the subduction of the Pacific plate under the Eurasian / Okhotsk / Philippine and down in the southern hemisphere. But that southward component? That part that gives me earthquakes right now (and volcanoes ‘not so much’… unless it changes ;-)? Where is THAT coming from?
This would work better on a sphere, but this is what we get to work with on 2-D computer screens, so just remember the actual geometry is spherical, OK?
Age of the Seafloor showing Spreading Zones
Notice how the active spreading zone in the Atlantic wraps right around the Arctic and “ends” near Siberia? The crust is “younger” near it, and ages as you move out. The Arctic was once smaller, and as it spreads and gets bigger around it, the continental plates get moved out. Not a lot (the color band is narrower than in other places) but ‘enough’.
http://en.wikipedia.org/wiki/Gakkel_Ridge
The ridge is the slowest known spreading ridge on earth, with a rate of less than one centimeter per year. Until 1999, it was believed to be non-volcanic; that year, scientists operating from a nuclear submarine discovered active volcanos along it. In 2001 two research icebreakers, the German Polarstern and the American Healy, with several groups of scientists, cruised to the Gakkel Ridge to explore it and collect petrological samples. Among other discoveries, this expedition found evidence of hydrothermal vents. In 2007, Woods Hole Oceanographic Institution conducted the “Arctic Gakkel Vents Expedition” (AGAVE), which made some unanticipated discoveries, including the unconsolidated fragmented pyroclastic volcanic deposits that cover the axial valley of the ridge (whose area is greater than 10 km2). These suggest volatile substances in concentrations ten times those in the magmas of normal mid-ocean ridges. The AGAVE expedition also discovered on the Gakkel ridge, using “free-swimming” robotic submersibles, what they called “bizarre ‘mats’ of microbial communities containing a half dozen or more new species”.
But hey, I’m sure all the Arctic science is now “settled science” ;-)
Personally, I suspect that the spreading zone doesn’t just end there, but gets covered up as it dives under Siberia (see: http://en.wikipedia.org/wiki/Laptev_Sea_Rift ) and “pops up” again over in Alaska (and maybe also that skinny line headed toward Canada below Greenland). Just, at the moment, it’s under a continental land mass that it can’t pull apart and the Atlantic spreading is keeping the bits shoved together. Basically, for now, the Atlantic spreading is beating it at that location. If I’m correct, that means any ‘bending’ or ‘stretching’ as things ‘head south’ ought to come out of Alaska and that end of Siberia rather than Japan.
Other Things
If you notice, the color bands in the Pacific are much wider than anywhere else. The Pacific is spreading faster than the other places. (Though Australia has been moving North at a good clip!)
So “what happened”? Why is the Atlantic spreading ‘winning’ at the moment? For the simple reason that the Pacific plate is subducting but the Atlantic sea floor is not. For more, see:
http://en.wikipedia.org/wiki/Seafloor_spreading
California into Nevada
Look at where that Pacific spreading zone hits North America. Notice that it’s splitting off Baja California? It continues up into the area of The Salton Sea and Death Valley (which is below sea level as the spit has caused the bottom to drop about 9000 feet. It’s only as high as it is because about 9000 feet of sediment has fallen in to fill the ‘crack’…) Then it wanders on up toward the rest of the Basin and Range Provence where the crust is rather thin and flat. Why is the “Basin and Range” thin? Because as the continental USA is shoved south it gets geometrically stretched and thinned out. It can take a while to stretch a continent in two… (remember that point about things need to get wider as they get shoved ‘around the bend’ and into a wider part of a spherical shape?)
It is generally accepted that basin and range topography is the result of extension and thinning of the lithosphere, which is composed of crust and upper mantle. Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth. Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block.
If you start seeing a whole lot of quakes out there, and with some drop of elevation, well, it’s just nature asking if you would like sea front property in a few tens or hundreds of millions of years ;-)
Volcanoes and Me
So, IMHO, the answer to “why am I not getting volcanoes?” is pretty simple. Further north (Alaska), the land is on an east /west line, but moving south. Subduction and volcanoes. When the land lies North / South: At Cascadia, the spreading is back off shore, so subduction ashore with quakes and volcanoes. Further south, Mexico, spreading is in the Gulf, so volcanoes inland. For me, I’ll only get the Volcanoes return when the spreading rifts enough to give more subduction (millions of years). Or if the other side of the Pacific Plate gets stuck and stops subducting quite so much… the whole plate could get shoved a bit more this way instead, but I think the Philippine plate has to be consumed before that happens. Then again, a little pickup in either the Atlantic spreading rate OR the Pacific rate (under me) and we could “pop one”. The deep red end of the scale is “zero to 9.7 million years” and we had the Sutter Buttes pop up just 1.5 Million years ago. Lassen erupted in 1914 (though it’s just enough north of me that I don’t need to worry…much… “this behaviour is by design” ;-) Things can “hiccup” from time to time. After all, it was only a SMALL volcano ;-)
So while it’s fairly unlikely for that to happen again, the spreading age shows that things have not really changed much between then, and now…
Rifting
One speculative bit: I note that Mammoth Lakes / volcano is just about where one would project the spreading zone to be. I have to wonder if it represents the place where the rifting has started to break through the surface…
The wiki gives an idea how much attention is put on this idea:
http://en.wikipedia.org/wiki/Gulf_of_California_Rift_Zone
The Gulf of California Rift Zone (GCRZ) is the northernmost extension of the East Pacific Rise which extends some 1300 km from the mouth of the Gulf of California to the southern terminus of the San Andreas Fault at the Salton Sink.
The GCRZ is an incipient rift zone akin to the Red Sea Rift where continental crust associated with the North American Plate is being pulled apart by tectonic forces and being replaced by newly-formed oceanic crust and seafloor spreading.
That’s it, the whole thing. 2 Sentences. And they have it ending at the Salton Sea. Nevermind that Mammoth Supervolcano caldera or all those other volcanic features in central California… Everything is either ‘past’ or ‘earthquake fault’ from there to Cascadia…
Those folks who are looking at it, tend to look in Mexico. This paper has a 2003 date citation in it, so is fairly new:
http://www.data.scec.org/NARS-Baja/NARS-Baja.pdf
Introduction
The Gulf of California (GofC) extends
~1300 km from the fast-spreading midocean
ridge system of the East Pacific
Rise to the San Andreas Transform Fault
zone in southern California. One result
of the last 6 myrs of deformation, which
has been active over the full length of
the Gulf, is that the Baja California
peninsula is now part of the Pacific
Plate. On the Sonora conjugate margin,
there is a zone of active basin and range
type extension. Crustal deformation
within the Gulf itself ranges from classic
ridge-transform structures in the south to
diffuse deformation in the north. The
GofC is an excellent place for studying
the rifting process because both sides of
the rift are accessible, and the history of
plate interactions in this area is well
known.
Geophysically, the GofC is largely
unexplored.
http://en.wikipedia.org/wiki/Mammoth_Mountain
Mammoth Mountain was formed in a series of eruptions that ended 57,000 years ago
[…]
The volcano was formed from a long series of eruptions that started about 110,000 years ago and lasted to perhaps 57,000 years ago, although the volcano is still active with minor eruptions; the largest of which was a minor phreatic (steam) eruption 700 years ago.
[…]
Mammoth lies on the South end of the Mono-Inyo chain of volcanic craters, some of which erupted as recently as 250 years ago. Mammoth Mountain is on the southwestern edge of Long Valley Caldera, a large area that subsided after an enormous eruption 760,000 years ago. The Mammoth Mountain magmatic system is considered distinct from that of Long Valley caldera and Inyo Craters.
Sure like how they think it’s all ‘distinct’… just because the rift that runs under all of them circles 1/2 the globe, that’s no reason to think they are connected ;-)
http://en.wikipedia.org/wiki/Long_Valley_Caldera
Near the center of the caldera there is a mound called the “resurgent dome” that was formed by magmatic uplift. The area is still volcanically active and has periodic rhyolitic lava flows.
…
The history and deposits of the Mono and Inyo Craters overlap with Long Valley Caldera in time and space. The Mono-Inyo Craters volcanic field developed along a 30-mile-long (50 km) fissure system that extends northward from Mammoth Mountain on the southwestern rim of the caldera to Mono Lake.
The interesting bit, here, is that these volcanoes are not subduction volcanoes… While we’re not quite up there with Iceland, this is an interesting place as it is where the “rift meets the land” and mid-ocean spreading heads to the mountains…
The fun bit to ponder: Where does it go from there? It ends up back out to sea off the coast of Northern California, so you can draw a line from Mono Lake to the Cascadia Subduction Zone. What do you find? Lassen, Shasta, Eagle Lakes… and the volcanic fields of Northern California, plus more: http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_california.html ( Though note that they call it the “past” having embraced the “new normal” of the length of a couple of human lifetimes…)
The Cascades include Shasta, and head off inland (over the subduction area) from northern California on through Oregon and Washington. Yes, they matter. But that they are subduction features does not mean you can ignore the rifting zone south of it, nor our ability to “pop a volcano” in unexpected places, should nature decide to give it a go… The Sutter Buttes, where I grew up, are just about where you would project that rift from the coastline toward Mono lake crossing that wide empty very non-volcanic valley. The Geysers and a hot springs region is on the other side of it. The most fascinating part of it all, for me, was growing up in this odd place where subduction is so near, and rifting so near, and they hold in balance for so long some times. But don’t ever think it’s over or that “this time is different”. It’s just a moment to digest past excesses…
Cascade Volcanic Arc
So could California have a new volcano just show up, anywhere along that rifting line from the coast to Mono lake? Could it have an old one give a mighty burp from there on down to the Gulf of Mexico? “You Betcha!”. (Though rifting could also ‘just stop’). And that’s why I watch that gulf area for quakes so much, and the Mammoth Mountain area too. Because just after that, the old rift ‘makes a hard left’ heads over the fields and valley, and very near to me (in volcano terms ;-) Basically, as long as the Arctic is pushing things south “enough” to overcome the desire to spread here, no volcano. But if it ever gets ‘out of balance’ or if the spreading zone ‘straightens out’ a little as the land spreads ‘going around the bend’, or if the San Andreas doesn’t keep that little block shoved up against the rift zone enough, well “things change” some times…
So for now, I get to enjoy life “balanced on the edge” of the forces of subduction, geometric stretch, land spreading, rifting, volcanism, and slip quakes. Ah, “Life On The Cusp!” Gotta Love It!
Musings from the Chiefio 
There is one additional dynamic in the mix with the spreading of the basin and range region. The Farallon plate subducted at a rather shallow angle. At some point in the fairly recent past, the piece to the East of the center seems to have “broken off” and started to sink down into the mantle.
As that plate was subducting, it cause the North American plate to “bunch up” a bit and the crust in what is Nevada would have thickened. Now that it has “broken off” and has started to sink into the mantle, that stress has been relieved and the West Coast has started to “relax” somewhat. The most obvious indication of that is the Garlock fault zone where the land North of the fault is moving Westerly in relation to the land South of it. But in response to the more general Southerly movement of North America as a continental mass (actually rotating counterclockwise) the Garlock fault is probably giving way to the newly forming White Wolf fault to express that relaxation.
Notice there are two motions:
1. A rotation around the Euler pole of the plate which is Quebec.
Click to access 540PlateTectonics.pdf
2. A general Westward push from the spreading center in the Atlantic. The result is an overall Southwesterly movement.
EM if you go to this address, it pictures how japan moved during the earthquake.with arrows. Pretty neat pic.
Also of note is this GPS vector map — this shows with arrows of different sizes and orientations the motion vectors of different spots on Honshu as a result of the event, its foreshocks, and its aftershocks:
Above is the caption describing the pic. Sorry, I don’t know how to insert it.
http://blogs.agu.org/mountainbeltway/2011/03/12/the-morning-after/
Forgot to add, it does appear that the eventual fate of Honshu is to be split off to the east, if the arrows are any indication.
I went to this place from the AGU one. EM If you haven’t been to one of these supersites, you need to go here. Do it before the market opens tomorrow, or you might miss a trade, it’s got that much data to peruse.
http://supersites.earthobservations.org/sendai.php
OK, I have to admit I have always had a hard time swallowing the whole subduction theory. My first question is simply, how does the spreading areas, being based on hot magma coming through cracks, generate enough horizontal force to build up the pressures we saw exhibited so dramatically in the 9.0 Japan earthquake????
Why doesn’t it just burn more holes and squirt harder???
The second issue is that we are told that the subducting plate drags along large amounts of water and other more frangible material. If there is enough room to carry this material, yet there is so much force, why aren’t the subducting interfaces squirting magma all over the place along the subduction interface rather than through volcanoes only marginally connected to the subduction zones???
Another theory item is that the more dense plate goes under the lighter plate. The Pacific Ocean plate is subducting on all sides. It is thinner and, with the ocean, less dense than the surrounding continental plates. WTF?!?!?! Why don’t all these plates simply FLOAT on all this hot magma instead of being driven under each other??
http://davidpratt.info/subduct.htm
This page covers information from a paper seemingly driving nails into plate tectonics. Please note that the journal this paper is published in also has the author of the paper as a member. While I believe the data is correct, I could have been fooled!!
Definitely follow the links to Pratt’s other papers. Very interesting look into the inconsistencies of a supposedly hard science.
“why aren’t the subducting interfaces squirting magma all over the place along the subduction interface rather than through volcanoes only marginally connected to the subduction zones???”
They probably would if it subducted straight down, but it doesn’t. It slopes down at an angle and it must go many miles before it gets hot enough to melt the material.
“Another theory item is that the more dense plate goes under the lighter plate. The Pacific Ocean plate is subducting on all sides. It is thinner and, with the ocean, less dense than the surrounding continental plates. WTF?!?!?!”
Ocean plates are basalt which is really dense. Continental crust is mostly granite which is much lighter. Most continental mass will always float along on top of the various plates, even if it all comes together again and breaks up again.
Think of it like “slag” floating on top of molten metal.
Hmmm, if the abiotic oil formation theory that it forms because of pressure, the presence of water and carbonates where subduction is occurring, it would seem that there should be oil to be found along the Chilean coast and maybe inland as well …
George, slag floats on top of water???
What is under the granite of the continents??
Read the links I provided.
I read it, or most of it.
There is an additional possibility: there could be a three-way split, such as is happening in northeast Africa, where the Rift Valley splits southwest from the Red Sea at the Afar basin.
From roughly the Salton Sea there is a line of earthquakes which runs northeast all the way to the Wasatch Front (Utah), then north almost to Yellowstone. It looks like the system wants to open a rift in that direction, though it might fail to turn into a long-term spreading sea….
*Personally*, I don’t think it is going to rift at all. At least not much North of Death Valley if it even gets that far. Now that the old plate segment on the East side of the spreading center has fallen away into the mantle, the spreading center will simply dissipate under North America. What remains of the Western side will likely fall away, too. But once that East side fell away, there is no longer a well-defined rift there. There is simply a more general plume that can spread out under the continental land mass.
This is a pretty good article on the subject:
http://blogs.agu.org/magmacumlaude/2008/05/20/accretionary-wedge-9-cenozoic-magmatism-and-the-subduction-of-the-farallon-slab/
Awesome article I hope u do more geology and volcano ones. Do u think the megathrust plate near BC and seatle may go again soon like 1700 or will another nova erupta in Alaska go again I notice redoubt is smoking again this week
@Tim Clark:
Neat movement markers. Looks like the middle was hung up on a ‘point’ and let loose…
I’m watching CNBC World right now. Tokyo markets down about 6%-7% and yen down a bit (BOJ injecting liquidity like crazy and it’s still not falling all that much?…)
The general rule is “buy the rumor, sell the news”, that would have had a bunch of shorts on at the start of the event, then now as things hit the “news is out, plunge of the Mom & Pop Seller” is when you “cover shorts and go long”.
So IFF I do anything with Japan today, it’s likely to be “buy some way crazy depressed golden companies like Honda and Toyota” where large chunks of their production and sales are from non Japan factories…
Basically, Japan is on sale with about a 10% discount… Just avoid things with a big insurance exposure and / or things with a big coastal infrastructure they just lost… ( i.e. I’d pass on that Fukusima Fish Packing company and the Sendai Vegetable Market…)
But in any case, let the charts be your guide or use “trailing orders” like a ‘buy if touched’ to buy you in when the reversal day comes.
@Interesting Connections:
You mean like this find:
http://www.energy-pedia.com/article.aspx?articleid=139448
though otherwise it’s a bit sparse.
http://www.eoearth.org/article/Energy_profile_of_Chile
The major point that would be a “dig here” is that it would take carbonate rock formation (that may not be in the subduction zone here) along with the right level of heat (to not cook it all the way to CO2 or natural gas) and may further require some particular catalyst rock types (i.e. zeolites or similar or high iron content like banded iron). Basically, it may be more than just subduction… but subduction with “reactor parts’…
@Scarlet Pumpernickle:
I think Cascadia is next. Just don’t ask me in which century ;-)
@Kuhnkat:
Slag floats on top of heavier slag… Granite is a light density, basalt very heavy. About 2.7 sp gravity vs 3.0 or so. Sandstone is about 2.0 and shale about the same. Water is 1.0 and iron is 7.8 so very heavy. A continent is where all the “light scum” gets floated as the mantle turns over dumping heat via the magma cycling.
You can see the process happen in minature at “lava lakes” (google “lava lake youtube” for more examples, this is the first one I found… I’ve seen better:
So we have a “hot spot” where stuff is just bubbling up like crazy, just like the hot spots under Hawaii and Yellowstone. You have large plates of “scum”, and you can watch some of them as they cool that are more dense than others start to go under at one edge, and just sink. During the close up of the hot spot, you can see lighter scum diffentiating into a scum layer that gets pushed to the side and even though it cools, piles up and doesn’t sink. It’s the same process on the global scale, just a lot slower (and a lot cooler due to the water, which raises the viscosity and slows things down too).
In most parts of the crust the magma is not inches away from the cold air, but miles, so the plates are much more stiff and much more slow to move (and tend not to sink wholesale). The magma flowing away from hot spots and / or long fissure erruptions (not all of it comes out the hole) tends to induce viscous drag on the bottom of the plate, pulling it sideways (you can see that in the scum next to the hot spot in the film).
So chemical fractionation puts the lighter stuff (like basalt) on top of heavier hotter stuff (like iron rich magma) and has the granite “scum” bunched up in continets. The viscous drag of the convection drags the basalt sideways. In some cases, it does NOT sink (such as along the Atlantic coasts) in others it’s just dense enough, and the physical profile of what’s it’s being pushed against is just shaped right, for the edge to start bending down and sinking. Once this begins, it tends to feed on itself (Again, visible in the film where you can see a plate form and just sink starting at an edge)
(You can make stuff that behaves like this at home and at much lower temperatures too. I’ve seen “stuff” on the tops of some things I’ve cooked act similar to this. I think it was a cream soup…)
So there isn’t really any hard to explain bits here. Just “light crap floats, heavy crap sinks, and convection puts viscous drag on the bottoms”…
OK, that means your first questions are based on a false premise. It’s not the force squirting UP that matters, it’s the bit that does NOT go through the hole, but heads out sideways, that makes the drag force…
Per the “crap on top along for the ride”. You have to look closely at the way the plates dip to explain that. As they start going down, they make a ‘trench’. The plate they are going under does tend to scrape some of the crap off, and that stays in the trench, but eventually enough builds up to have some (lubing the top of the subducting plate) pressed into the layer on top. AS it goes further in, the water starts to be pressed / cooked and things get a bit glued together. Far enough down these “hydrate rocks” have a lower melting point and lighter specific gravity than the basalt, so they melt first and slowly start to errode a way to the surface, but boyancy sends them straight up a couple of miles, not back on a slope of 20 miles. Thus the volcano inland over the melt zone.
It’s like feeding a long slightly damp pole into a fire. The heat and fire go up, not back down the pole…
Yes, the Pacific + water a bit more dense than the continent. (Though do remember that at the subduction zone the coninental margin is usually under a load of that water too). It’s pretty well defined. If anywhere is too heavy (say it’s 2.5 sp gr average and the basalt were a 3.0) and had, oh, 1.5 x the height of the surrounding basalt, that would make it 3.75 total vs 3.0 for the basalt. If the water was as thick as the basalt, it would only add a 1.0, but you get a total of 4.0. So the force on the bottom of the Basalt is a 4 while that on the bottom of the continent is a 3.75, and it will slide over that edge, which starts to bend down, pulling more basaltic crust down. That is now a 3.0 density with a 3.75 continent over it for a total of 6.75 and it heads down more (pulling the part behind it along until it melts, too)
So the bit at the subduction point is getting a bit of ‘pull down’ and a lot of “slide under” while the center is getting a load of “spread out” via viscous drage on the bottom side.
Oh, and the interface is not all liquid like water or hot magma you see at volcanoes. No, that’s the high hydration stuff. It’s very liquid. The deeper magma is more like honey, very viscous, lots of drag, and moves slow. You get the fast stuff where water is involved, like where that subducted scum is hydrating the rock as it melts.
Yes, I read the link. So he found some odd stuff and others have found some odd stuff. That does not mean that the process isn’t what happens; it just means that (as he put it) “cartoons” carry an IDEA and not a full and rich reality. Real rocks are messy things.
I’d expect a load of odd inclusions. Strange fractures (as that subducting plate will not go quietly into that dark hot hell). I’d EXPECT it to bend and Fault and FRACTURE along the way (just as the land above it bends, folds, fractures, and faults). It’s not melted until it’s way far down. And some crap is likely going to be stuck in it that melts at different temperatures.
FWIW, I’d also expect to find that a plate all of 10 miles or so thick and 6000 miles long is going to be a bit ‘flexible’ and ought to be prone to some degree of bucking and buckling. So I’d not be at all surprised to find islands in the Pacific bobbing up and down as the plate bucks and shudders. (Part of why I think using sea level to measure climate is daft…) So could you find some chunk that had been bent up into an island (with surface rocks) then sucked down into ocean floor later? Frankly, I’d expect it.
There are modestly reliable stories of islands rising, then later being sunk. We have sea floor in the Himalaya and Colorado. “stuff happens”. And just because the Pacific Plate is subducting today does not mean it must forever. Or has forever. Various plates have various ages as bits break off. Some survive longer than other.
It’s more like a “Rocky Road” candy bar than a “Milky Way”. And one that was in your pants pocket when you ran a mile… Yeah, messy.
So he found some more ‘texture’ to things than the ‘cartoon’ model. Doesn’t mean much. Things still subduct. We still have trenches and ocean floor ages and continental rock types and ages and… well, and Iceland getting bigger spreading both ways and California mountains rising (in some cases over the course of my lifetime…)
On example: India smacked into Asia and gave us the worlds tallest mountains. With sea floor rocks on top… Now nothing prevents those rocks, and maybe even some igneous rocks too, from ending up rifted back into sea floor at some future time (like, oh, maybe that Rift Valley forming in Africa… could scrub some rock chunks off the walls and back into the new sea floor. Little bits of crap all over. Yet the rift was still there, and still formed when it did, even if other age rock bits are mixed into the candy… And a new force could shove that rift shut and hold it there for a few million years too (like the one under California)…
So in the middle of the “sedimentary” Central Valley of California is this “smallest mountain range in the world”. It was a 6000 foot volcano at one point. Now eroded down to about 2000 ft. Dormant or dead. The whole place could get rifted off of the main chunk of N.America and eventually dumped out to sea. Stretched thinned crust sinking it into the ocean (as the Basin and Range is thinning today and may someday go back to being ocean bottom).
Does that igneous rock on the bottom mean that NO subduction happens? Nope. It only means that SOME non-subduction crustal thinning can happen too. And we already know that…
So yes, the cartoon subduction is over simplified. All teaching tools are. Yes, the real world is much more complicated and messy. But the basic processes are still there and still right. Even scat Jazz still has chords in it…
@Eric Fithian:
“Classic” spreading theory holds that all rifting starts as a bulge that makes a “3 way” split in the top, of which 2 survive and one fails. The “$64 Billion Question” is:
Do I get my Central Valley Volcano again, or does Yellowstone open a split to Mexico? Jury is out (and it may depend on how far under the continent that basic rifting zone really is… and does the whole thing just quench now that it’s under 20 miles of granite and the convective flow changes…
@George:
You may well be right. They seem to die once covered by a continent (except that Africa thing nags at me…) and I don’t remember where I saw it, but I remember a statement that the sinking rate of the bottom of Death Valley as it is spreading was one of the fastest on the planet…
We don’t have a lot of experience with “mid ocean ridges” under land masses. Iceland argues for spreading and land accumulation with volcanoes. We’ve got spreading (some from ‘basin and range’ processes, some from the rift near Mexico) and volcanoes. Just need the magma and land accumulation in the rift… Siberia argues for “just dies”… The mess in the Indian ocean (and edges) argues for a dice roll.
Unfortunately it will take a few dozen million years to know for sure which of us is right ;-)
(I knew there was a reason I wanted to be a geologist 8-)
Personally, I expect things to start and fail to rift a few times as stresses wobble and change before it finally “makes up its mind”. Like it popped the Sutter Buttes in a clear start of rifting volcanism, then just said “Never Mind”… as some force or other changed just enough.
Actually doing some deep water study of the bottom of the Gulf of California might tell us if it’s still doing anything interesting, or not…
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0015399
BTW anyone see this article, very interesting for Abiogenic Oil :P
The gabbroic layer comprises the majority of ocean crust. Opportunities to sample this expansive crustal environment are rare because of the technological demands of deep ocean drilling; thus, gabbroic microbial communities have not yet been studied. During the Integrated Ocean Drilling Program Expeditions 304 and 305, igneous rock samples were collected from 0.45-1391.01 meters below seafloor at Hole 1309D, located on the Atlantis Massif (30 °N, 42 °W). Microbial diversity in the rocks was analyzed by denaturing gradient gel electrophoresis and sequencing (Expedition 304), and terminal restriction fragment length polymorphism, cloning and sequencing, and functional gene microarray analysis (Expedition 305). The gabbroic microbial community was relatively depauperate, consisting of a low diversity of proteobacterial lineages closely related to Bacteria from hydrocarbon-dominated environments and to known hydrocarbon degraders, and there was little evidence of Archaea. Functional gene diversity in the gabbroic samples was analyzed with a microarray for metabolic genes (“GeoChip”), producing further evidence of genomic potential for hydrocarbon degradation – genes for aerobic methane and toluene oxidation. Genes coding for anaerobic respirations, such as nitrate reduction, sulfate reduction, and metal reduction, as well as genes for carbon fixation, nitrogen fixation, and ammonium-oxidation, were also present. Our results suggest that the gabbroic layer hosts a microbial community that can degrade hydrocarbons and fix carbon and nitrogen, and has the potential to employ a diversity of non-oxygen electron acceptors. This rare glimpse of the gabbroic ecosystem provides further support for the recent finding of hydrocarbons in deep ocean gabbro from Hole 1309D. It has been hypothesized that these hydrocarbons might originate abiotically from serpentinization reactions that are occurring deep in the Earth’s crust, raising the possibility that the lithic microbial community reported here might utilize carbon sources produced independently of the surface biosphere.
Look at where that Pacific spreading zone hits North America. Notice that it’s splitting off Baja California? It continues up into the area of The Salton Sea and Death Valley … Then it wanders on up toward the rest of the Basin and Range Provence where the crust is rather thin and flat.
Errr… no. Not the way I learned it, at least. The East Pacific Rise (spreading zone) does run up through the Gulf of California, but it doesn’t go north or northeast from there. It zigs northwest to re-emerge off north-central California — the San Andreas Fault is a gigantic transform fault that connects the two segments of the East Pacific rifting zone. Transform faults do not, as a general rule, produce volcanism. They’re tectonic features only. The Basin and Range province is far inland of the San Andreas, and has an entirely different geologic origin.
Much of the West Coast’s geology can’t be understood fully in the simple context of ‘the Ring of Fire.’ It’s much more complex than that, largely because there are two separate sets of plate motions involved. The North American Plate has been moving westward for the last sixty-odd million years, driven by the spreading along the North Atlantic rift zone. As it moved, it overrode the plate which used to be east of the Pacific Plate — a plate that paleogeologists call the Farallon Plate. This subduction generated all the stuff you expect to see from subduction, including earthquakes, volcanism, mountain-building, etc. The Rockies, the Basin and Range, the Sierra Nevada, the volcanism of the Colorado Plateau, the uplift of the Plateau itself, and most of the recent (as in, last couple of million years) volcanism up and down the US West Coast are all associated with the ongoing subduction of the Farallon Plate under the North American Plate.
Overlying this older set of motions, you have the newer set that you spent much of this post talking about (and very nicely done, too): the North American Plate interacting with the Pacific Plate.
An interesting thing to consider: the East Pacific Rise is a spreading zone between the Pacific Plate and the Farallon Plate, which otherwise hardly exists anymore! Virtually all of it has been subducted under the North American Plate. I’ve never seen anyone try to model what will happen when the NA Plate tries to override the spreading zone itself, but I suspect it will be very interesting.
@Wolfwalker:
Perhaps you didn’t notice the word “speculative” in the “rifting” lead in?
So yes, the "classical" explanation is the rift is failing and turning into a transform fault. My "speculative bit" is that it has had 'moments of life' such as that 1.5 MYBP formation of the Sutter Buttes (not anywhere near the San Andreas, and in between two uplifting mountain ranges…and formed LONG after the Farallon plate was long gone).
That comes after the earlier statement that it heads out toward the 'Basin and Range Provence", but that area covers from Mexico (i.e. the landfall at the end of the Gulf of California) and up into Nevada. So to say it heads up 'into the Basin and Range Province" does not require that it reach all the way to Idaho , it mostly just says "comes ashore and heads north"…
And, IMHO, the split that is Death Valley is showing that same spreading sinking floor action. (And it's right next door to Nevada on a straight projection of the line of the Gulf of Mexico). Note that I am NOT saying that the Basin and Range process is a result of a rift (though in comments there is speculation that a rift could someday head toward wyoming). I'm just speculating that the Farallon plate subduction explanation does not account for all the known facts, while another fairly simple idea does account for the missing bits.
Also note, that this idea is NOT in conflict with the notion that the Farallon plate caused some large part of what we see. In fact, it’s a part of the Farallon plate thesis to a small degree:
http://en.wikipedia.org/wiki/Farallon_Plate
That idea is that the spreading zone is trying (and to some degree having a bit of sporadic success) to cut through the continent. So we get Death Valley, Long Valley, and Mono Lake, and those otherwise very hard to explain Sutter Buttes; as fairly far north on the Nevada border the process turns toward the sea (where we see it reappear).
So contrary to the assertion that “it is all plate subduction” the Farallon thesis allows for rifting too.
All I’m doing is putting my best guesses about where that rifting pressure is acting now (though I could easily be wrong and / or the fluid flows could always wobble back and forth a bit too and move it around).
@ kuhnkat
Thank you for the link to the David Pratt… very interesting… and wonderful reading.
My first instinct is to stand back from plate tectonics and have a think about the planet earth.
The standard theory regarding the earth is that it condensed out of stuff flying around the sun. The important word here is condensed because it implies cooling. This means the earth has been cooling since its creation and at some point a cool, hard crust formed on the earth. It is also argued that the earth is still cooling due to heat radiation, volcanic venting and geothermal activities.
Now one of the very noticeable effects of cooling is contraction. This implies that a cooling earth is also a shrinking earth… and if the earth is shrinking then I would expect the crust of the earth to crack to form a mosaic of plates of different shapes and sizes… and that this cracking would be a continual process as cooling continues. [My analogy would be a chocolate covered red balloon :-) cover your inflated balloon in hot chocolate… leave it to set… then start to release the air from the balloon very slowly… observe what happens].
David Pratt’s view seems to be based upon a similar view… a mosaic of plates… plates that are subsiding, uplifting and tilting… with volcanic and sedimentary layers overlaying and infilling… that gives uplifting mountains and ocean trenches… and as tilting plates subside they dig deep into the crust and could make volcanic pathways and channels…. so we have gravitational (and magnetic) forces acting on out-of-balance plates… possibly some convection currents from deep below stirring things up as well.
A quick look at the Rock of Gibraltar indicates that some of these plates can be very small… that plates can turn through 90 degrees… while some of the plates are on a continental scale and have deep roots into the earth… and I don’t think this view precludes some plates being subducted here and there… it is just that subduction is a side show and continental drift is just a nice bedtime story… the plates might be having a party… but they are not circulating with the other guests… they are not drifting around the venue… they are standing at the bar having too many drinks until they keel over :-)
I also think it is very possible that the earth is very dynamic… the earth originally shrunk as it began to cool… but as it shrunk it became more dense… and perhaps it reached a critical mass and initiated a nuclear process in the core… so it is possible that the earth has gone into reverse and that it is now warming and expanding from the inside. [Going back to my chocolate covered red balloon analogy… think about what happens when you start inflating the balloon… the chocolate cracks and you start to see the red balloon through the cracks].
To answer this question you probably need to compare the earth to the moon. The moon is a lot smaller than the earth so it should have cooled quickly… it fact it now looks like a very dead, cold rock that solidified so quickly that it incorporated a tidal bulge in the rock pointing towards earth. Now take a look a the earth… it is a lot bigger than the moon and should cool at a slower rate… but it also has a far larger surface area that can be used to radiate heat… but its cool crust is very shallow… possibly too shallow for its age… so we have to go back and resolve the energy budget of the earth before we can really understand what is going on… but either way it seems a good bet that the crust of the earth is cracking up into a mosaic of plates :-)
http://davidpratt.info/subduct.htm
http://davidpratt.info/lowman.htm
http://davidpratt.info/tecto.htm
Click to access Leybourne_Oceans_Fin.pdf
Interestingly, the East Pacific Rise has a 1:1 correlation between earthquakes on it and El Nino. Thus this important fault in a way determines the planet’s weather….
Where is the pile of debris at the subduction zones that has been scraped off the plate being subducted. This has theoretically been ongoing for hundreds of millions of ye
Let’s try that again,
Where is the pile of debris at the subduction zones that has been scraped off the plate being subducted. This has theoretically been ongoing for hundreds of millions of years. There should be enormous piles of sediment, fossils, all the light slag, piled up at these subduction zones. There simply isn’t.
kuhnkat: I’m not a geologist, but if I understand the little I’ve read on the topic right, the easternmost part of north Honshu is
exactly such a “pile of debris” – an accretionary prism.
@Scarlett Pumpernickle:
Fascinating article. “Weather” in the mantle…
but which way does causality flow? Magma to sea and air, or air to sea and magma? Or perhaps electricity and magnetism to both….
@Kuhnkat:
Well, look at the major subduction zones and you find incredibly deep trenches, but not as deep as the soundings show for the top of the very dense layer. All that “muck” trys to fill the trench, but some is getting sucked down at the bottom (especially as it lithifies with depth and age and pressure and heat). So SOME accumulates making a wedge, then it gets into balance with the amount being pulled down with the plate. You can “try this at home”. Put butter on top of one hand, spread out, palm up. Slide it against the other hand palm (start at finger tips toward wrist). You WILL get a pile of butter at the “subduction edge” but you will also find the part that got scraped still has butter on it. (Especially in the unconformity ares like that gap between the fingers or when you hit the depression in the palm). Plates are even less uniform than your hand…
These folks have a pretty good write up. You can also observe the actual motions of stuff like this the real world. In fact, in California, you can live on some of the accumlated, bent folded stuff that was bulldozed off the subducting plates as the continent pushed over them. The mountains of California are full of layerd, bent, folded sediments complete with sea shells and sharks teeth. (My highschool biology / geology teacher took us all to the local hills to see for ourselves…) What WAS in a subduction zone got piled up into mountains as that subduction zone got swallowed by the continent (as described above).
http://www.absoluteastronomy.com/topics/Oceanic_trench
You can also find lots of article by folks surveying individual piles of ‘stuff’ if you do a search on: Accretionary prism seismic profile
For example:
http://www.cprm.gov.br/33IGC/1344023.html
So yes, those “piles of stuff” are out there, and are being looked at all over the world. Just don’t expect them all to look the same (as the “stuff” in them varies, the deposition rates vary, the thickness in the area of approach varies, the subduction rate varies, the lithification rate of sediments varies, the …. )
from: http://worldwidescience.org/topicpages/n/nankai+accretionary+prism.html
and
So you see, they are there, and in the case of Japan are even being very closely studied as this big piles of softer stuff may be the major cause of tsunami.
They are more like “jello” when compared to the basaltic plate that is subducting, and they tend to get cracks and deformations as things move, then in the “spring back” they wobble more (those ‘reverse faults’) and make a generall mess of things.
So, in a way, the whole tsunami that just hit Japan can be seen as evidence of just such a “pile of debris” being shaken at the subduction zone…
Don’t get too worried about the latest theories on geophysics. It is just as flaky as the theories on climate.
Why has no one brought up the Sierra Nevada granite batholith It actually runs from under the coast range to the edge of Nevada and from Mt Tehame cauldura to the Tehachapies. This is tipped down to the west and the west edge is covered with the bulldozed material of the subducted Farralon plate. Just look at the coast range material. Fairly resent seabed materials. This subduction no longer happens at the present time. and the fault merly slips The Sierra batholith is the very ancient core of what once was a very great mountian range. There is a 100 mile displacement at the fault from about Cresent City past Susanville, The Trinity Mountains are also part of the original granite. Pg
The east pacific rise is definitely something that needs to be further looked at for El Nino. The sea does warm, but it’s not sure why it does.
Do a search for the terms East Pacific Rise seismic activity and the start of El Nino and you will find info.
Eg
http://www.offshore-mag.com/index/article-display/23488/articles/offshore/volume-56/issue-3/news/general-interest/gas-economics-how-el-nino-affects-the-us-natural-gas-industry.html
The East Pacific Rise
Some geologists and geophysicists have different ideas involving heat flow from hydrothermal plumes and subsea lava flows along mid-ocean ridges. There may be a plate tectonic drive mechanism (Shaw and Moore, 1988).
Dr. Daniel Walker at the University of Hawaii has been collecting seismic data in the Pacific Ocean for years, and notes that surges in earthquake activity near the East Pacific Rise (EPR) coincide with the onset of El Nino events (Walker, 1995; Walker, 1988). The northern East Pacific Rise extends about 3000 miles from Baja to Easter Island, and is described as an ultra-fast spreading center, with spreading rates of 11-16 cm/year in some segments. Roughly three to five ft of fresh lava are extruded every 10 years along this trend.
The crest of the northern EPR is not very deep: -1,690 to -2,650 meters (National Geographic Society – 1992). An inspection of the EPR during 1984 by the submersible Cyana (Renard et al, 1985) found semi-extinct black smokers venting 0C water (note – this was not an El Nino year). During April 1991, the submersible Alvin found fresh lava flows just two weeks old and a “tubeworm barbecue” where recently parboiled tubeworms lay rotting next to black smokers venting 400C low density water, hydrogen sulfide, metals and methane (Haymon et al, 1993). This was just after the start of the 1991-1992 El Nino event, and followed a pulse of increased seismic activity during February, 1991 (Walker, 1995).
In November, 1993, an oceanographic expedition cruised slowly along the EPR “yo-yoing” a logging tool up and down (Urabe et al, 1995). They concluded that 60% of the portion of the EPR which they surveyed was venting hot water in hydrothermal plumes. These observations followed a pulse of high SST during the summer of 1993 (Figure 2 [47526 bytes]).
* How much venting occurs during a severe El Nino?
* What happens to the hot water rising above the ridge, and how is it dispersed by currents?
* Could the hydrothermal plumes cause sea-surface temperature anomalies?
These questions cross several scientific disciplines and haven’t yet been clearly answered. But, if hydrothermal activity is an important cause of El Nino, additional subsea instrumentation along the EPR (hydrophones, seismographs, temperature monitors, etc.) might provide an early warning system.
http://rsta.royalsocietypublishing.org/content/368/1919/2481.abstract
http://www.terracycles.com/joomla/sections/1-earth/10-elninovolcanism.html
It looks like earthquakes can effect the weather….
We know the core also controls the weather
http://www.terradaily.com/reports/NASA_Study_Goes_To_Earth_Core_For_Climate_Insights_999.html
Thanks for wrapping your mind around this one offering new ways to think about plate movements and what “they” might be up to. Not much time, but I have been enjoying the plate v plume debate; it seems to add to the scientific discussion. I don’t know if the following from mantleplumes.com adds much to the CA rift issue, but it offers some new ways to think about “hot spots” and grabens: “Subduction-triggered magmatic pulses: a new class of plumes?”.
http://www.taipeitimes.com/News/taiwan/archives/2011/03/15/2003498234
Japan warned about underwater volcanoes as well
@ Scarlet Pumpernickel
good points re El Nino, persionally i think this (Nino & sister)
explain the major climate shifts (every x years) we humans need to worry about, read your history books (forget CO2, maybe :-)
but what do i know, only read others & try to make my best estimation.
ps. great blog E.M – what other site has the host contributing so much as here.
american tv – get this guy a science/life slot.
I mean there is a 1:1 correlation. But noooooooooooo lets keep looking at CO2. CO2 doesn’t explain El Nino at all, and it’s the most powerful weather force on earth, it can make a break civilizations and it’s continually ignored over and over even though people have known about it for a long long time
@ Scarlet Pumpernickel
if hydrothermal activity is an important cause of El Nino
Then it would put another nail in the coffin of the team’s energy budget…
visualize a soccer ball