[Bass]

The photo was snapped at Mammoth Hot Springs near the nothern edge of Yellowstone Park.  The rocks are made of travertine, which is deposited from the hot springs.  Mammoth Hot Springs has the most abundant deposits of travertine in the park.  
In most of Yellowstone, the geysers and hot springs precipitate sinter (or geyserite)- composed of silica which the thermal waters dissolve as they pass through the volcanic material.  Silica sinter accumulates slowly- in the order of a few centimeters per century.
Because travertine is calcium carbonate, the thermal waters at Mammoth must pass through older, probably Mississipian-aged, limestones.  Travertine accumulates much more rapidly than does silica sinter, in the order of 40 to 70 cm/year- thus the massive formations of travertine at Mammoth.  The travertine also dissolves easily, so as the pathways of the thermal waters change, voids often form- which is what I believe created part of the formation in the picture.
As an aside- the thermal springs at Mammoth are not as hot as those found more central to the park- suggesting that they have travelled some distance before bubbling up to the surface.  The travertine preceipitates as the water cools at the surface, forming small pools.  As these pools grow, the water flows over the edge of the pool where it is shallowest, further cooling the water and leading to more precipitation- in this way the edges of the pools build up.

Prediction is difficult, especially the future.  -Niels Bohr

[Bass]

Plate tectonics predicts that mountains will form at the edge of plates.  This seems to hold true for almost all mountain ranges on earth- even those ranges found in continental interiors (Urals, Himalayans, Alps) formed along the edge of a tectonic plate.

Question of the week:  THE ROCKY MOUNTAINS (USA) ARE APPROXIMATELY 2000 KILOMETERS FROM THE EDGE OF THE NORTH AMERICAN PLATE- HOW DID THE ROCKY MOUNTAINS FORM (AND WHY ARE THEY STILL GROWING TALLER) SO FAR FROM THE EDGE OF THE PLATE?



Prediction is difficult, especially the future.  -Niels Bohr

[ukmicky]

Hiya skip
I'm not quite sure how it all works. But are they the type of mountain that is created by the folding of the earths crust, an area of land that sits in between two plates that are pushing together. Something like that, I think

Michael                                      

[Bass]

Your hypothesis is spot on for the Himalayas, Alps and a few other mountain ranges- but there is no evidence of a junction of plates along the Rockies.  As far as I know- the North American plate extends all the way across the US (with the exception of a small piece in southern California).

Prediction is difficult, especially the future.  -Niels Bohr

[neilep]

Thanks for a great question Skip.

I'm stumped !..the mountains are not on the edge of the plates and Michaels
 answer above doesn't cut it either eh ?...and yet these mountains are
 growing !...is there some sort of lava making activity happening below,
 beneath the Rocky Mountains that is pushing them up ?...there has to be
 something that is making more mountain.


Men are the same as women.... just inside out !!

[Bass]

Neil- you’re on the right track.
This conundrum even stumps the folks that study plate tectonics (plate tectonicists?).

An initial short length, a bit of lengthening, and lots of shallow thrusting, is the best hypothesis put forward to date (quit panting Neil).

1.   Initial short length:  When the Rockies began forming, in
the Laramide orogeny (~75 to 55 million years ago), the coast was
several hundred kilometers closer.  The Farallon plate was being
subducted beneath North America close to the California-Nevada border.
2.   A bit of lengthening:  The Great Basin has been undergoing
extension of at least 2 cm/yr for the last 16 to 20 million years
(300-400 km)- so the subduction zone was even closer yet.  This is
probably due, in part, to the NA plate over-running the Farallon
spreading ridge.
3.   Lots of shallow thrusting:  The oceanic crust (Farallon
plate), being thinner and heavier than the continental plate, was
subducted beneath the NA plate- leading to compression and sliding
stacks of rocks along “thrust” faults long distances to the east.  
Apparently, instead of sinking into the mantle at the typical angle
of around 45 degrees, the Farallon plate stayed almost horizontal,
this stacked up thrust zones much farther to the east than the
norm.  Volcanism started around 50 million years ago, which is
additional evidence of a descending slab beneath the Rockies.  
Present uplift of the entire Rocky Mountain region indicates that
tectonic processes are still active- i.e. that the slab is still
scraping the bottom of the crust.

Here is a normal subduction zone


Compared to  horizontal slab subduction:

If you’ve ever been in a room with two or more geologists, you’d
soon discover that they can’t agree on much of anything.  In tune
with our disagreeable nature- there are several other hypotheses.
(BTW- Only a small piece of the Farallon plate exists today- called the Juan de Fuca plate off the coast of Oregon, Washington and British Columbia- the rest has been over-run by North America).

Subduction causes orogeny.

[neilep]

Skip, you're very generous to say that I was on the right track, of course your explanation was going to be my next guess !![]

....Thank you for the explanation. It's all very facinating stuff.

Men are the same as women.... just inside out !!

[James Bowkett]

I'd agree with the theory of reduction spots. As for animal tracks, if you head to Almeria in Andalucia it is possible to examine large sedimentary basins and there is evidence of the Messianian salinity crisis, proof of which can be round the whole of the med. While there we saw deer tracks.

Can't find name of locality at present though.

James[]

[Bass]

The following pictures are from lava flows





QUESTION OF THE WEEK:
These flows have a very distinctive "ropey" surface texture.  Name the flow texture?

Bonus questions:
Name the type of lava?
What does this tell you about the explosiveness of the volcano?
Where is the source of the molten rock (lava)?


Subduction causes orogeny.

[neilep]

Come on peeps..have a go...I'm stumped...This is one for Exodus.

Thanks for the quiz Bass.

Men are the same as women.... just inside out !!

[ukmicky]

As i don't speak Hawaiian? i had to cheat. but because i cheated i learnt something, so in the end its all good.
but as a respectable member of society i feel it would be wrong of me to answer the questions.

Skip,
 I know what the bottom flow is called but just one question before i go to bed and place my head on my Pillow[] is the top picture taken underwater.

Michael                                      

[Bass]

Oops!

I forgot to draw the little fishies in...

Actually, that is some sort of rabbit brush or small sagebursh growing on the flow- so not underwater.  This texture probably won't form underwater- the lava cools too fast.

Subduction causes orogeny.

[Bass]

The “ropey” flows are called pahoehoe (pronounced like a pig squeal), the Hawaiian word for either “run like hell”, or “does it suddenly feel hot to you?”  

Actually, it means smooth lava, in contrast to aa, which is rough lava.

Pahoehoe forms when the surface of low-viscosity lava flows began to cool and develop a plastic skin,  As the lava continues to move underneath, it pushes the skin into lobes, giving it the characteristic “ropey” look.

Pahoehoe only forms in basalt.  Basalt is a low-silica, high temperature lava- which means low viscosity.  Since basalt is low viscosity, it happily flows across the ground and doesn’t accumulate volatile components like its more explosive cousins, andesite and rhyolite.  That makes basalt eruptions, such as Hawaii and Iceland, safe enough to view and study up close.

The temperature and components of basalt argue for a deep source, most likely the uppermost mantle.  Basalt is by far the most common volcanic rock on earth.


Subduction causes orogeny.

[Bass]

Pictured here is a primary depositional feature common in sedimentary rocks.  Note the change in attitude of the beds where the person is standing from those above and below.  



GQOTW:  Name this sedimentary feature.  

Bonus
What type of sedimentary rock is this?
Given the large scale of this feature, what was the most likely  environment during deposition of these sediments?


Subduction causes orogeny.

[Bass]

The sedimentary feature here is called cross-bedding. Cross-beds are internal sedimentary structures formed by currents of wind or water. Cross beds are deposited on the lee side of ripples (subaqueous) or dunes (wind caused)- as granular sediment (usually sand) rolls down the steep advancing edge or "foreset slope" of the dune.  Commonly, the next sedimentary layer erodes the top of the cross-beds, leaving a sharply defined angular discontinuity.



The sedimentary rock pictured here is a sandstone.  The large scale of the cross-beds indicates it probably formed by wind-blown dunes- the depositional environment is most likely desert (possibly beach).  Water-laid cross-beds are much smaller.

Subduction causes orogeny.

[Bass]

This photo is from Missoula, Montana.  Note the prominent horizontal banding, which is displayed quite well by snow on the mountain slope.  

GQOTW:  How were these horizontal bands formed?  (the underlying bedrock is oriented almost vertical)

Bonus:  What impact did this have on landforms in Washington state?

FYI:  The formation of these horizontal bands and their impact was one of the most controversial geologic debates in the 1930's to 50's.

Subduction causes orogeny.

[Soul Surfer]

That looks a bit like the stuff I saw on channel 5 the other night when they were talking about superfloods created by the failure of Ice dams on glacial lakes.

Learn, create, test and tell
evolution rules in all things
God says so!

[ukmicky]

Did the bands/layers start off horizontal but got pushed up into their vertical positions as the mountain went up

Michael  
HAPPY NEW YEAR                    

[Bass]

Sorry if my question was confusing.  The underlying bedrock is much older than the horizontal banding- bears no relationship to the banding.
Soul Surfer is on the right track, but what formed the horizontal bands?

Subduction causes orogeny.

[neilep]

Watched an amazing program last night/this morning . following the expedition to discover what really happend at the bottom of the sea that caused the tsunami from last year. They went 4 months after the event an it was astonishing the pictures and technology used, and quite humbling too when you see the shear scale of things.

Seems there was an amzing uplift of about 40 meters by 750 miles width  !!!...the whole worked like a zipper and took just a few seconds. The scary thing is, only part of the fault rose up and another is expected !!...at any time.

Men are the same as women.... just inside out !!