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Author Topic:   Introduction To Geology
Minnemooseus
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Posts: 3730
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 4.1


Message 69 of 293 (643293)
12-06-2011 2:44 AM
Reply to: Message 63 by Dr Adequate
12-05-2011 12:00 AM


Re: Glaciers - One quibble
...and in fact glaciers flow more swiftly near the top, as can be determined by hammering a flexible metal rod into a glacier and leaving it for a year or so: the rod will be bent at the top in the direction of flow.

The glacial horizontal velocity is greatest at the top because the that is the sum of all the flowage from bottom to top, not because the the plastic flow at the top is the greatest. Plastic flow will approach zero as depth approaches zero.

The below left is, as I understand it, your image of the bent rod (flow direction left to right); The below right is how I believe it would actually bend:


o o
o o
o o
o o
o o
o o

Added by edit: The above right is also wrong - See message 72 for what I think is correct.

Or something like that.

Something to look at:

Source

Moose

Edited by Minnemooseus, : Change ID.

Edited by Minnemooseus, : See above.


This message is a reply to:
 Message 63 by Dr Adequate, posted 12-05-2011 12:00 AM Dr Adequate has responded

Replies to this message:
 Message 70 by Dr Adequate, posted 12-06-2011 9:10 AM Minnemooseus has acknowledged this reply
 Message 71 by Dr Adequate, posted 12-07-2011 7:07 AM Minnemooseus has responded

    
Minnemooseus
Member
Posts: 3730
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 4.1


Message 72 of 293 (643549)
12-08-2011 12:26 AM
Reply to: Message 71 by Dr Adequate
12-07-2011 7:07 AM


Re: Glaciers - One quibble
First of all, I blotched the "bent rod" diagram. It should have been:


o
o
o
o
o
o

The horizontal displacement at the bottom is greater because the internal plastic flow is greater.

The other diagram in message 69...

...illustrates the total displacement in a certain amount of time (the vertical velocity profile). As it says at diagram bottom: AC is total movement, AB is sliding at the glacier base, and BC is the internal plastic flow. Actually, the various BC's are summations of all the internal plastic flow from the base up to a given height. The vertical velocity profile line approaches vertical at the ice top surface because the plastic flow rate approaches zero.

The ice at the top may have the lowest rate of flow, but doesn't it also have the highest velocity?

The top ice has the highest flow rate (velocity) relative to the base of the glacier (or in general, the fixed rock). That's because it is the sum of all the flow rates, bottom to top.

You can't really see the vertical flow rate profile because it's buried in ice. You can see the lateral flow rate profile. But the essence of it all is that glaciers advance by some combination of basal slip and internal plastic flow. I believe that in some cases the glacier base can frozen to the rock below - There is no basal slip component. If there is no basal slip component, then there is also no erosion happening.

By the way, glaciers retreat when the front ablation rate (melting etc.) exceeds the flow rate. The glacier does not start flowing the opposite direction.

Moose

Added by edit: I'm still not sure I didn't blotch up some of that plastic flow theory.

Edited by Minnemooseus, : See above.


This message is a reply to:
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Replies to this message:
 Message 73 by Dr Adequate, posted 12-08-2011 2:33 AM Minnemooseus has acknowledged this reply

    
Minnemooseus
Member
Posts: 3730
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 4.1


Message 134 of 293 (666899)
07-01-2012 2:55 AM
Reply to: Message 131 by Dr Adequate
06-29-2012 11:07 AM


How do the S waves get to the inner core?
I note that there are velocities for the S waves in the inner core. It seems to me that the outer core would filter out the S waves - The S waves could not get to the inner core.

Moose


This message is a reply to:
 Message 131 by Dr Adequate, posted 06-29-2012 11:07 AM Dr Adequate has responded

Replies to this message:
 Message 135 by Dr Adequate, posted 07-01-2012 4:09 AM Minnemooseus has acknowledged this reply

    
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