NASA to study active volcanoes in Alaska and Japan using images from...
A NASA aircraft carrying a unique 3-D aerial radar developed by NASA's Jet Propulsion Laboratory, Pasadena, CA, has left California for a 10-day campaign to study active volcanoes in Alaska and Japan.
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“Geologist [I'm Climate Change]”
Since: Mar 07
#1 Oct 3, 2012
Japan is an interesting spot to study as Tohoku region underwent "rebound/long duration Mercalli X" (r/lx) quake last year, which relaxed the crust.
This is important as the usual result of convergence is to direct max compressive stress in convergence zone horizontal with the result that magma extracted from the dewatering descending plate cannot simply get to the surface as there is a lot of compressed rock in the way and instead the magma ponds in discs at the base of the "crust" between 60 and 120Km down, dependent strongly on which arc it happens to be.
In absence of crustal relaxation, catastrophic melting of the crust and a rising supervolcano sized pluton would ultimately pop up through the crust forming a large caldera surrounded by a sillar sheet (as happened in the Altiplano 15 to 5Ma before it began backarc spreading properly).
R/lx happens to pop out the forearc along the megathrust with as a result, a large tsunami (~30m in this case in the N. at Iwate, and ~15m in the S. at Fukushima). This crustal relaxation allows the formation of fractures full of magma in the arc, which then move horixontally according to the stress field during subsequent recompression until they hit either... The arc graben, a segment boundary transform fault, or a sector more compressed than its current location. At that point the magma in the deep crustal fracture set can go in only one direction with further compression (up), with obvious stratovolcano formation @ the surface with a magma composition typical of basic magma with a long residence time at depth (high alumina basalt, Andesitic basalt, or basaltic andesite. The aftershock sequence of the Tohoku r/lx was very noticeable in the fact that there was a lot of forearc & descending plate activity and the arc region with its injecting basic magma filled fractures was practically aseismic. The megathrust frictional melt has now frozen & the megathrust locked so the recompression stage is now underway.
There is likely in Tohoku to be a rather long volcanic gap (about a decade) before the gas rich magma inported during the last r/lx gets diverted to the surface, most of it will eventually emerge in the N. part of the Tohoku region around Iwate & Towada Ko.
Last event incidentally resulted in a long fracture crossing the entire tohoku region and emerging at the least compressed part of the zygomorphic arc (megathrust on BOTH sides and pproximately 2* the runout of a classical arc). This therefore indicates the part of the arc with the largest runout last time. The volcano active as a result was Asama, its last eruption was 3 years before the Tohoku r/lx when the Andesite volcano erupted rhyolite derived from the partially molten fracture walls. Asama will now likely be dormant for a long time as the Tohoku r/lx runout was smallest @ the volcano.
Volcanism therefore gives an important indicator of the direction & runout of the last r/lx. The vector, runout, and plate convergence direction will therefore also give a VERY important clue to the nature of future volcanism in the region.
As it is the very early stage of recompression, the auto levelling from space will probably give a negative result as a result of the deep basic magma largely travelling sideways for a while.
have a nice day: Ag
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