images of juan de fuca (OT but geology related)

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Messages 1 - 45 of total 45 in this topic
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Original Post - Jul 24, 2010 - 12:33pm PT
General plate-tectonic map of the NE Pacific Ocean showing the North American, Pacific, Explorer, Juan de Fuca, and Gorda plates. The Juan de Fuca Ridge extends from West Valley to Cleft Segment, along the W margin of the Juan de Fuca plate. The seismic swarm discussed in this report lies within the darkened rectangle. The darkened circle shows the approximate location of the April 2001 Gorda Ridge seismic swarm. Courtesy of Bill Chadwick and NOAA.


apogee

climber
Jul 24, 2010 - 12:38pm PT
Very interesting and very cool. Thanks for passing it along!
Reilly

Mountain climber
The Other Monrovia- CA
Jul 24, 2010 - 12:48pm PT
Very illustrative, thanks! I take it the green dots in the second represent population?

One thing I've always wondered is 10 the theoretical max on the Richter scale?
Seems like for the Sierras to pop up out of the sea bed it would take something more.
Tony Bird

climber
Northridge, CA
Jul 24, 2010 - 12:55pm PT
an open-ended logarthmic scale. a 9 is 10 times an 8. a 10 is 10 times a 9.

the good friday earthquake in alaska (1964) was possibly a 10.
BooDawg

Social climber
Paradise Island
Jul 24, 2010 - 01:06pm PT
Great Illustrations of a geologically complex area! I love it that there are postings like this on S.T. Do you have one that shows the different terranes (small bits of micro-plates) that have drifted in from elsewhere and been melded or melted or fused to the W. edge of the N. American plate?
Reilly

Mountain climber
The Other Monrovia- CA
Jul 24, 2010 - 01:08pm PT
Tony,
I know it is logarithmic but open-ended implies there can be greater than 10, right?

The AK quake has been determined to be 9.3 or 9.4 the last I checked.
My best friend there was in bed in Anchorage when it hit. It threw him
and his three bros onto the floor from their bunkbeds. For the ensuing
four minutes they couldn't even get to their knees to crawl out of their
bedroom! He described the scene as a bowl of goldfish dumped on the floor.
Mighty Hiker

climber
Vancouver, B.C.
Jul 24, 2010 - 01:35pm PT
The geoglogists estimate that there is a magnitude 9 earthquake on the Juan de Fuca plate every 300 to 500 years. The last one was January 26th, 1700 - pinpointed by tsunami records from Japan. For more pictures and stuff: http://en.wikipedia.org/wiki/1700_Cascadia_earthquake
Such a quake would cause many deaths and enormous damage in southwest BC, western Washington, and western Oregon.

There probably was a person named Juan de Fuca, who claimed to have reached 47 degrees north on the west coast in 1592 (from New Spain/Mexico), but it's quite unclear whether he did. http://en.wikipedia.org/wiki/Juan_de_Fuca

(Francis Drake in the Golden Hind probably also didn't get so far north in 1578, despite claims from his boosters to the contrary. If he did get so far north, it led to no results.)
Reilly

Mountain climber
The Other Monrovia- CA
Jul 24, 2010 - 01:39pm PT
Given Drake's larcenous nature it is hard to see what would have motivated
him to go so far north. Besides, where you gonna play at bowls along that coast?
Tony Bird

climber
Northridge, CA
Jul 24, 2010 - 01:43pm PT
it's not the bo derek scale, more like the YDS. you got a better one, we can handle it. wait'll that asteroid finds its way in.

my bro moved to alaska, fortunately after 1964. but there are plenty of anecdotes like that. full grown pine trees in the city park whipping back and forth all the way to the ground. water coming into the fjords hundreds of feet above sea level, people scrambling to get higher, not all successful. on good friday a lot of people thought it was the end of the world.

btw, i believe the richter scale is maximum intensity. there's also something called seismic moment. think YDS versus grade III, IV, etc., but i could be wrong about that. time for a real know-it-all to speak up.
Thorgon

Big Wall climber
Sedro Woolley, WA
Jul 24, 2010 - 02:03pm PT
Geology Bump! Didn't Baker blast some steam about 1980? We would like to think it is dormant! LOL

Thor
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 24, 2010 - 02:30pm PT
from Wikipedia...

The Juan de Fuca Plate, named after the explorer of the same name, is a tectonic plate, generated from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone.

The smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted under the North American Plate.


here is an image from a 3D USGS model showing the depth in km to the top of the subducting J de F plate and earthquakes
http://pubs.usgs.gov/ds/91/

Here's the text that goes with these figures
We present an updated model of the Juan de Fuca slab beneath southern British Columbia, Washington, Oregon, and northern California, and use this model to separate earthquakes occurring above and below the slab surface. The model is based on depth contours previously published by Flück and others (1997). Our model attempts to rectify a number of shortcomings in the original model and to update it with new work. The most significant improvements include (1) a gridded slab surface in geo-referenced (ArcGIS) format, (2) continuation of the slab surface to its full northern and southern edges, (3) extension of the slab surface from 50-km depth down to 110-km beneath the Cascade arc volcanoes, and (4) revision of the slab shape based on new seismic-reflection and seismic-refraction studies. We have used this surface to sort earthquakes and present some general observations and interpretations of seismicity patterns revealed by our analysis. In addition, we provide files of earthquakes above and below the slab surface and a 3-D animation or fly-through showing a shaded-relief map with plate boundaries, the slab surface, and hypocenters for use as a visualization tool.

this one shows a cross section
TGT

Social climber
So Cal
Jul 24, 2010 - 03:22pm PT
Hm,

Never realized that the JDF plate was a true independent plate with a spreading zone on the west side.

Wonder if it's going to produce a volcanic island arc some day.

Plenty of precedent on the west coast. That's largely what makes Calif Geology so interesting.
nature

climber
Tucson, AZ
Jul 24, 2010 - 03:28pm PT
I'm particular to the Gorda plate myself, Juan's little brother.

I was in Humboldt when the three ~7.0's hit in 1991.

Doing graduate work there in Geology was a pretty bad ass experience. Gary Carver is a madman and a genius. A fair amount of what we know about Cascadia is attributed to his work (both along the north coast and Alaska).

Baker blasted steam more recently than that. 1981 St. helen's blew. I lived in Tacoma at the time. Saw the mushroom cloud out my back window. Watch TV all day long when the massive eruption occurred. Sure am glad the winds were blowing the other way.

One thing I've always wondered is 10 the theoretical max on the Richter scale?
Seems like for the Sierras to pop up out of the sea bed it would take something more.

A lot of little events went into jacking the Sierra Nevada microplate up 10,000+ feet. if it went all at once the Richter scale would be meaningless.

Next time you drive HWY 395 look at the eastern escarpment of the Sierra and think of it as being a 10,000 foot high normal fault.
Reilly

Mountain climber
The Other Monrovia- CA
Jul 24, 2010 - 04:10pm PT
Mt Baker in more like '75 ...
It sounded waaay scary!


tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 24, 2010 - 05:11pm PT

Mt St Helens May 17 09:00
Mt St Helens May 18 08:35
Jaybro

Social climber
Wolf City, Wyoming
Jul 24, 2010 - 05:22pm PT
Nature, all genius' are madmen/women, just the price of admission.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 24, 2010 - 05:36pm PT
Developed in 1935 by Charles Richter in collaboration with Beno Gutenberg, both of the California Institute of Technology, the Richter scale was originally intended to be used only in a particular study area in California, and on seismograms recorded on a particular instrument, the Wood-Anderson torsion seismometer.

Richter arbitrarily chose a magnitude 0 event to be an earthquake that would show a maximum combined horizontal displacement of 1 micrometre on a seismogram recorded using a Wood-Anderson torsion seismometer located 100 km from the earthquake epicenter. This choice was made to prevent negative magnitudes from being assigned. However, the Richter scale has no upper or lower limit. Sensitive modern seismographs now routinely record quakes with negative magnitudes.

Because of the limitations of the Wood-Anderson torsion seismometer used to develop the scale, the original ML cannot be calculated for events larger than about 6.8. Many investigators have proposed extensions to the local magnitude scale, the most popular being the surface wave magnitude MS and the body wave magnitude Mb.

REF: http://www.wordiq.com/definition/Richter_magnitude

The Richter scale has been largely replaced by the Moment magnitude scale (MMS) to estimate magnitudes for all modern large earthquakes by the United States Geological Survey. The MMS is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulae are different, the new scale retains the familiar continuum of magnitude values defined by the older one.

The energy released by nuclear weapons is traditionally expressed in terms of the energy stored in a kiloton or megaton of the conventional explosive trinitrotoluene (TNT). A rule of thumb equivalence from seismology used in the study of nuclear proliferation asserts that a one kiloton nuclear explosion creates a seismic signal with a magnitude of approximately 4.0.

REF: http://en.wikipedia.org/wiki/Moment_magnitude_scale
Hardly Visible

Social climber
Llatikcuf WA
Jul 24, 2010 - 05:58pm PT
Boodawg,

You may have to zoom in to about 200% to read these but here's a sampling of accreted terrains in the north cascades.



I'm pretty sure everything cretaceous or older drifted in from somewhere else.
Then of coarse a little furter north and west you have Vancouver and The Queen Charlotte Islands most of which is now thought to have come from equatorial latitudes.

tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 24, 2010 - 06:24pm PT
Hardly Visible: you are referring to "Wrangellia" (named after the Wrangell Mountains in Alaska) shown here in this Late Cretaceous Paleogeographic reconstruction from Paleogeography Google Earth. Wrangellia is the terrain just west of the 2 large land masses, the Canadian Shield and Eastern N America...this is before Wrangellia collided and accreted on to N America forming what is now Western North America. The yellow outline showing the present location of N & S America is there for reference.

tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 24, 2010 - 07:40pm PT
Then of coarse a little further north and west you have Vancouver and The Queen Charlotte Islands most of which is now thought to have come from equatorial latitudes.

Yes this is based on the remnant paleomagetic vector preserved in volcanic rocks & sediments. Here is a recent paper that suggests these terrains may not have originated so far south...

Late Cretaceous paleogeography of Wrangellia: Paleomagnetism of the MacColl Ridge Formation, southern Alaska, revisited

John A. Stamatakos1 Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, San Antonio, Texas 78238, USA
Jeffrey M. Trop Department of Geology, Bucknell University, Lewisburg, Pennsylvania 17837, USA
Kenneth D. Ridgway Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, USA

GEOLOGY August, 2010

Volcanic and sedimentary strata of the Late Cretaceous MacColl Ridge Formation were sampled and demagnetized to reevaluate the paleomagnetically derived paleolatitude of the allochthonous Wrangellia terrane. Characteristic directions from 15 sites representing ∼750 m of the MacColl Ridge Formation (80 Ma) reveal a reversed-polarity primary magnetization yielding a paleomagnetic pole at 126°E, 68°N, A95 = 9°. Comparison of this pole with the Late Cretaceous reference pole for North America indicates 15° ± 8° of latitudinal displacement (northward) and 33° ± 25° of counterclockwise rotation. In contrast to previously reported low paleolatitudes (32° ± 9°N) for the MacColl Ridge Formation, these new results place the Wrangellia terrane at a moderate paleolatitude (53° ± 8°N) in the Late Cretaceous.
nature

climber
Tucson, AZ
Jul 24, 2010 - 07:44pm PT

autochthonous Donkey on the JDF.
Mighty Hiker

climber
Vancouver, B.C.
Jul 25, 2010 - 01:32am PT
An interesting bit of toponymy - Kevin's favourite new word.

The area including the Strait of Juan de Fuca - that is, the Strait, plus Georgia Strait and Puget Sound - was recently renamed the Salish Sea. The Coast Salish of various sub-groups being of course the original inhabitants of much of its coasts. I don't believe that they called it the Salish Sea in pre-contact times, though.
http://en.wikipedia.org/wiki/Salish_Sea
Hardly Visible

Social climber
Llatikcuf WA
Jul 25, 2010 - 11:35pm PT
Tuolumnne tradster,

Wrangellia is what I was referring to. It is interesting how long north to south it appears in that Late Cretaceous Paleogeographic reconstruction that you show in your post, it looks like a pretty substantial addition to western north America that could not have all come from 53° N. I know some geologists think that part of the Seven Devils Mtns.in northeast Oregon is Wrangellian, it wouldn’t surprise that something in California might turn out to be Wrangellian too. Along those lines I wouldn’t have a hard time believing that a sample in Alaska could have 15° ± 8° of latitudinal displacement whereas a sample from Vancouver Island might have 39° ± 6° latitudinal displacement since the accretion of Wrangellia was a long process that by no means was uniform and contemporaneous.

Here is an abstract for a study supporting substantial northward migration for at least some of Wrangellia:


Paleomagnetism of the westcoast complex and the geotectonics of the Vancouver island segment of the wrangellian subterrane

D.T.A. Symons

Department of Geology, University of Windsor Windsor, Ontario, Canada

Abstract
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.



Mind you that I’m just a rank amateur at all this so I won’t pretend to understand any of that mumbo jumbo except for the last sentence of it.

Here’s a couple of diagrams showing plate vectors of the Kula and Farallon plates off the Washington
and Oregon coast in Paleocene to early Eocene time indicating an increase in velocity and obliquity in
the subduction of the Kula plate about 59 million years ago.


Estimates for the velocity of the Kula plate during this time run somewhere between 4 to 8 inches per
year, which over the 4 million years between 59 to 55 million years the Kula plate would have moved
something a minimum of 250 miles northward.
All interesting stuff to ponder at any rate.
neebee

Social climber
calif/texas
Jul 25, 2010 - 11:38pm PT
hey there say, all... thanks for the interesting share... and the alaskan quake info, too...

very interesting...
god bless...
:)
nature

climber
Tucson, AZ
Jul 25, 2010 - 11:42pm PT
whoa... HV... that's way kula!

(sorry, my inner stoner is showing).
Jingy

Social climber
Nowhere
Jul 26, 2010 - 12:42am PT
Based on that last image (in the original post)...........


It'd be impossible for California to drop into the ocean, right.

Seeing how it is basically be held in, and lifted, by the pacific plate.. that "IS" dropping under the North American plate...

Has anyone told the right wing about this?
Jaybro

Social climber
Wolf City, Wyoming
Jul 26, 2010 - 04:32am PT
california moves west, subducting the rest....
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 27, 2010 - 12:53am PT
H V: thanks for posting that abstract. By progressively heating (thermal demganetization) the WC gneiss rock samples from Vancouver Is it is possible to determine the rock's original thermal remnant magnetism. The thermal demag essentially erases any weaker magnetic signals or "overprints" in the rock caused by the fact that the rock has been exposed to 10 of millions of years of the earth's magnetic field which has undergone random reversals every few 100K years. Once the sample has been "magnetically cleaned" of any overprints and the "true" thermal remnant magnetic vector is determined this vector reflects the orientation of the earth's magnetic field at the time the rock cooled. An apparent paleo pole can be determined using this palomagnetic vector.
For example,
WCB component (> 560°C) with a pole at 335°W, 66°N
means that the apparent paleo pole determined from the WC rocks was located near southern Finland (I think I did that correctly). Because the time-averaged magnetic field is a geocentric axial pole (i.e. roughly averages to be coincident with the rotation axis), it is not the magnetic pole that was in southern Finland but the WCB terrain that was ~33 degrees south of where it is today.

Hope this makes sense.

Here's an animation that I posted on another thread from the USGS website that shows 30 million years of movement along the San Andreas fault and its predecessors. It is a compilation of an enormous inter-disciplinary data set including paleomagnetic data from the Transverse range (watch it rotate ~ 90 degrees clockwise) and the correlation of Pinnacles to the Neenatch Fm ~ 300 km to the south. The stripes off shore are sea floor magnetic anomalies. Note that Juan de Fuca makes a cameo at the end.

http://earthquake.usgs.gov/monitoring/deformation/tectonics/western-na.mov

If you fast forward the animation in your imagination to 5 my in the future, Baja will be located adjacent to San Bernandino.
Hardly Visible

Social climber
Llatikcuf WA
Jul 27, 2010 - 01:45pm PT
TT,
Thanks for the explanation, I think I got the gist of it. I'd like to watch that movie you posted a link to but alas all I get is a blank page,
probably got to have some sort of movie watching program that I'm lacking??
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 27, 2010 - 09:51pm PT
HV: it's a Quicktime animation. I've run it on both PC & Mac.

Here's the website...
http://earthquake.usgs.gov/monitoring/deformation/tectonics/
tom woods

Gym climber
Bishop, CA
Jul 28, 2010 - 10:50am PT
Here's a bit of early history from the region. I do recall that the spanish did have a short lived settlement up there.

This one is a pre-Cook account of living among the natives of Nootka sound. It's a great story.



http://books.google.com/books?id=036jVbibDYUC&pg=PA30&lpg=PA30&dq=capture+nootka+sound&source=bl&ots=lfZ71y-ADv&sig=yA-0ofFHJ5_Cr8SVOzEwAmk8ElU&hl=en&ei=CEBQTOXfPJLWtQPBpqGyBw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCEQ6AEwAw#v=onepage&q=capture%20nootka%20sound&f=false
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 28, 2010 - 06:03pm PT
pre-Cook Nootka Sound bump
Mighty Hiker

climber
Vancouver, B.C.
Jul 28, 2010 - 07:15pm PT
Wrangel (Vrangel) was one of the governors of Russian America, born in Estonia. He was also a scientist and explorer, and of course from a wealthy noble family.
http://en.wikipedia.org/wiki/Ferdinand_von_Wrangel

The Russians were in fact much further ahead in exploration of their northern lands and waters than those in North America.
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 28, 2010 - 07:40pm PT
THE RUSSIAN PRESENCE IN AMERICA
by Marco Ramerini


The Russian explorers reached the Pacific through Siberia in 1639. The Tsar later sent two expeditions in 1728 and 1741 under the command of Vitus Bering and Alexei Chorikov, they discovered the Aleutian islands and Alaska. A profitable fur trade was established, Russian temporary settlements in the Aleutians and on Unalaska island began in 1770s. the first permanent outpost was built in 1784 at Three Saints Bay on Kodiak island by Gregorii Shelikhov. From there the mainland was explored, and other fur-trade centers were established. In 1786, Shelekhov set out for Russia, unsuccessfully seeking a grant to his company of monopoly of the fur trade. Shelekhov's company was the nucleus for the Russian American Company, which was formed several years after his death. By the early 1800s. Russian were exporting an average of 62000 fur pelts from North America. The first Russian Orthodox missionaries came to Alaska in 1794.


Fort Ross (named from Rossiia) was the southernmost outpost of the Russian presence in North America. The Russians remained at Fort Ross until the year 1841.
Today none of the original fort structures remain, however several buildings have been reconstructed: the first Russian Orthodox chapel south of Alaska, the stockade, and three other buildings, including the Commander’s House, which contains exhibits of the Russian-American Fur Company and the Russian occupation.
Hardly Visible

Social climber
Llatikcuf WA
Jul 29, 2010 - 04:10pm PT
Since we seem to be heading into human history of the region here's a link to a paper about village abandonment in the last 3000 years and how it correlates to tsunamis and earthquakes:

http://oceanlink.island.net/SOLE/LP/FN/SubZone_aband_quart_97.pdf
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 29, 2010 - 07:33pm PT
The Great Cascadia Earthquake of 26 January AD 1700

Coastal field work over the past ten years by many scientists from universities and federal, state, and provincial geological surveys in northern California, Oregon, Washington, and British Columbia has uncovered overwhelming evidence of a great (moment magnitude larger than 8) earthquake or series of earthquakes about 300 years ago. The earthquake (or earthquakes) was caused by the sudden slip of the Pacific plate beneath the North America plate along the Cascadia subduction zone, a 1000-km(600-mi)-long fault that marks the landward-dipping boundary between the two tectonic plates off the coast of western North America.


Some of the most convincing and best-preserved evidence of the earthquake(s) are sand layers that cover the peaty soils of coastal lowlands. A large tsunami that was generated by sudden movements of the ocean floor during the earthquake(s) deposited the layers when it inundated the coasts bordering the fault zone. The above photo shows such a sand layer in an exposure near the mouth of the Salmon River along the central Oregon coast about 8 km (5 mi) north of Lincoln City. One of the series of tsunami surges that probably followed the earthquake by 20 minutes to several hours picked up sand from the beach or dunes as it came ashore and deposited the sand as it moved up the river valley. At the site of the photo, the sand bed covers the remains of two fire pits dug by Native Americans, perhaps not long before the tsunami. The layers are well preserved partly because much of this part of the Oregon coast permanently subsided about 0.5-1.0 m (2-3 ft.) during the earthquake. The rise in sea level produced by the subsidence allowed tidal sediments to quickly bury the sand layers, protecting them from later erosion.

http://earthquake.usgs.gov/regional/pacnw/paleo/greateq/
Hardly Visible

Social climber
Llatikcuf WA
Jul 30, 2010 - 10:12pm PT
TT,
Here's another abstract for ya.

http://www.sciencemag.org/cgi/content/abstract/277/5332/1642

and a link to a geophysical study of the northern cascadia subduction zone

http://www.terrapub.co.jp/e-library/scpb/pdf/001.pdf
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jul 30, 2010 - 11:39pm PT
HV: thanks, that article really puts it all together nicely. These deep, large magnitude subduction zone earthquakes are the real devastating ones...add a tsunami and you have a real disaster on your hands. A rather ominous last sentence "a great Cascadia subduction earthquake of moment magnitude Mm = 9.2 is possible." The one that occurred in 1700 was obviously a big one.
Amanda Knisley

Social climber
Charlotte
Jan 17, 2011 - 07:44pm PT
Hi, I have been researching about Juan de Fuca Ridge but I cannot figure out why there are 8 million year old rocks on the west of the ridge and not the east?
tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jan 17, 2011 - 08:10pm PT
Amanda: the 8+ my old oceanic crust east of the Juan de Fuca ridge has already been subducted beneath North America.

tuolumne_tradster

Trad climber
Leading Edge of North American Plate
Topic Author's Reply - Jan 17, 2011 - 11:50pm PT
Here's a more detailed map of the Juan de Fuca plate showing the age of oceanic crust on either side of the spreading ridge. Note oceanic crust west of the ridge is > 15 million years; whereas, between the spreading ridge and the Cascadia subduction zone, oceanic crust is < 8 million years.

http://web.mac.com/drbohnen/MG_NCSU/Publications_files/mladenEPSL09.pdf

Gary

climber
Desolation Basin, Calif.
Jan 18, 2011 - 11:28am PT
MisterE

Social climber
Bouncy Tiggerville
Jan 18, 2011 - 11:37am PT
cliffhanger

Trad climber
California
Jan 18, 2011 - 12:01pm PT
1.5 miles deep in a black smoker on the Juan de Fuca Ridge off Washington lives an extremophile microbe (archaean) that thrives at 250 degrees F and can survive 266 degrees.


http://news.nationalgeographic.com/news/2004/05/0521_040521_extremeheat.html

http://www.genomenewsnetwork.org/articles/08_03/hottest.shtml


matty

Trad climber
under the sea
Jan 18, 2011 - 04:09pm PT
video here
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