Diverging The Southern Death Valley.

   The reason for the examination of the Snake River plain in one of my previous posts was to get a clue to processes behind Yellowstone caldera and a clue to forces that are global to the west of NA and are parallel to the coastline.

   Now, why not to search for other possible examples of intra-continental diverging processes? Why not to start with one of the most famous US valleys - Death Valley?  Its southern part, just around the Confidence Hills seems to show a good example of the process.
  
   Navigate to Shoreline Butte, Southern Death Valley, near Ashford Junction, California State Highway 178. South to this junction are the Confidence Hills. Set map mode to "Terrain" and have a look at mountains to South-West and at mountains to North-East of the Confidence Hills. Imagine, if the part of the valley the Confidence Hills are placed on, were shrunk, the mountains would fit each other quite nicely. Thus, at least this part of the Death Valley was formed by a diverging process.
  
   That's enough for a blog post, I think. The importance of the understanding that many (if not most) plains/valleys on the west of the USA were formed by the diverging processes is hard to overestimate. Particularly it's important in rethinking the Slab Gap Hypothesis, but let's leave it to another blog post.
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The Snake River Plain As A Divergent Boundary. Yellowstone Caldera.

   Let's take a look at The Snake River Plain satellite photo at: OSU, "The Snake River Plain and the Yellowstone Hot Spot" ( http://volcano.oregonstate.edu/vwdocs/volc_images/north_america/yellowstone.html ) [Accessed Jun-18, 2011]

   Let's consider Eastern part of the plain (the one that is closer to Yellowstone). Interestingly, for this part of the plain, its North-West border would fit exactly South-East border if the plain between borders gets cut off the image. And, as the ridges are very diverse in their shape on a distance even much less than width of the plain, the only explanation of it, I can think of, can be the divergent boundary formed perpendicular to the ridges. Assuming the divergent process is 1sm/year, it would take approx 10 million years to spread the plain. The divergent process may have stopped long ago for most of The Snake River Plain, but apparently not for its North-Eastern tip.

   It woud be very interesting to compare the plain's crust and relief to some oceanic (Pacific) divergent boundary's crust and relief. I've looked through approx a couple of dozens .gov and .edu sites on The Snake River Plain, - none of the sites mentioned that the borders of the East of The Snake River Plain would fit each other. Am I missing something?

   The possible scenario for Yellowstone Caldera can be that the divergent boundary had been developing pressure and trying to build its "Bridge Over Troubled Magma." (see http://divergent-boundaries.blogspot.com/2011/05/ridge-push-or-bridge-over-troubled.html and http://divergent-boundaries.blogspot.com/2011/06/tectonics-types-of-heat-transport-to.html ). As the process is relatively local (in comparison to oceanic divergent boundaries), it can't develop the force to break the plate and move its parts apart. Instead, the process would be pumping the top layer of the plate up. If the magma finds its way to escape the chamber, the volcano won't erupt.
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(edited Jun-20, 2011)
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Tectonics. Types Of Heat Transport To Develop Calderas, Volcanoes, And Divergent Boundaries.

   First two types of heat transport are obvious (let's not consider radiation heat transfer): heat conduction and convective heat transfer. And the third type is as described in "Magma Transportation On The Temperature Gradient" http://divergent-boundaries.blogspot.com/2011/05/magma-transportation-on-temperature.html

   Third type of heat transport explained.
   The concept of the third type is: Powered by deformations, crust propagates magma in the direction of lower temperature by the means of earthquakes, the magnitude of the earthquakes depends on many factors, among them are: amplitude and frequency of the deformations, crust characteristics, magma temperature, the value of the temperature gradient.

   Many would disagree on the third type. But is not it just a second low of thermodynamics in action? The first two types of heat transport move heat in the direction from higher temperature to lower temperature. Does not do the third type the same, though in its own way?

   No magic, if we have a transition zone between colder solid stuff and molten the same stuff, then, if we apply some chaotic action around the zone, the mother Nature has no choice in its response, other than moving the zone in the direction to colder stuff according to the second low of thermodynamics.

   Of course, the moving of the transition zone causes counter-action: say, gravity can be trying to get the molten stuff back. But don't we know from seismic observations that the magma is pumped up not in the form of some kind of a pipe, but rather in the form of scattered chambers? This way a local deformation has to pump magma between only neighbor chambers. Thus, regardless (almost) of the height of the vertical path, the local force of the deformation needs to be just enough to move magma to a neighbor chamber.

   The more chambers along the vertical path, the greater total force is to be applied. The divergent component of the force has to be compensated, say, in the case of divergent boundaries by subduction counter-force on the opposite side of the plate. The greater counter-force, the higher will be the ridge to build the divergent force to balance the counter-force.

   Calderas.
   The third type of heat transport can supply heat and develop pressure on its own with no help from hot spots and plumes.

   The concept of caldera development can be the next:

   - Some inter-plate or an intra-plate instance of the third type of heat transport mechanism is set up.

   - The transition zone on its way to surface meets some horizontally stretched irregularity that helps the transition zone to spread horizontally and blocks (at least for some time) the transition zone from moving up.

   - In the case the irregularity is air, magma is uplifted into the chamber, and we may assume the transition zone is the surface of the uplifted magma, no pressure in the chamber is developing yet. When magma fills the chamber, the transition zone is spreading further (including upward), pressure develops within the zone.

   - In case the irregularity is not air, the transition zone is spreading horizontally, the pressure is developed within the zone.

   - Further a number of scenarios can be suggested:

   Scenario 1. Uplifted magma and molten stuff finds its way out of the chamber forming a volcano outside the area. The pressure drops,  the top of the chamber collapses either at this time or when heat transport stops, say, for the temperature gradient disappeared and the uplifted magma and molten stuff gets down under the plate.

   Scenario 2.  Heat transport is intense and underlying plate is rather thick to maintain high pressure within the transition zone for a long time. There should be created a transition zone chamber between bottom and top plates. The top plate is strong and uniform to let the transition zone propagate uniformly upward within all the chamber area. The propagation, I'd expect to be heard as constant "roaring" as it effectively is a flow of micro earthquakes. When the transition zone is close enough to surface, the chamber blasts, the molten and semi-molten stuff of the chamber gets into air. As the chamber width, I'd expect, could reach a number of plate thicknesses, the amount of the stuff brought into air can be tens, if not hundreds cubic kilometers.

Volcanoes.
   The transition zone on its way to surface may meet relatively small horizontally stretched irregularity on no irregularity at all. In the latter case I'd expect the transition zone to uplift magma peacefully. The crust deformations would uplift magma until temperature gradient vanishes.

   In the case the transition zone meets some irregularity on its way to surface, the chamber is created. The chamber can store energy in the volume of compressed magma, in the form of compressed gases, in the form of elastic deformations of adjacent crust, etc.  So, when the transition zone finds finally its way to surface, the stored energy helps considerable amount of the transition zone stuff to blast up into air.
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   The important point about third type of heat transport mechanism is that it is heat transport mechanism, not exactly magma transport mechanism. Not much deep layer magma is expected to be among the uplifted stuff. And, the distribution of the uplifted stuff per depth it was sourced from, could be figured out. The precision of the estimations is important in crust's deep layers research.
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