# What force moved the glaciers? **URL:** \ **Category:** Factual Questions\ **Created:** [August 25, 2006, 9:44pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254 "2006-08-25T21:44:34Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [August 25, 2006, 9:44pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/1 "2006-08-25T21:44:34Z")
I know that mountain glaciers are pulled down by gravity but during the ice age what force pushed the glaciers from the north to the south? ---
**Author:** ![Lissa](https://avatars.discourse-cdn.com/v4/letter/l/85f322/32.png) [@Lissa](https://boards.straightdope.com/u/Lissa)\ **Post date:** [August 25, 2006, 9:48pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/2 "2006-08-25T21:48:17Z")
As I understand it, it was gravity again. Put an ice cube on the table. You’ll notice that a thin pool of water is created under it which “lubricates” the path. If your table has any uneveness or tilt to it at all, the cube will slide across the table to seek its level. The weight of the glacier itself melts some ice below it, creating the “lubrication”. Land is rarely flat. The glacier begins to slide into any lower elevation, and once that mass gets moving, it takes a lot to stop it. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [August 25, 2006, 9:51pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/3 "2006-08-25T21:51:36Z")
I agree that land is rarely flat. And this sounds good if the thousands of kilometers of travel were all downhill. Didn’t they have to go uphill too? ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [August 25, 2006, 9:54pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/4 "2006-08-25T21:54:34Z")
[QUOTE=solkoe] I know that mountain glaciers are pulled down by gravity but during the ice age what force pushed the glaciers from the north to the south? [/QUOTE] I’m not sure all glaciers moved north to south - the ones I’m most familiar with, which plowed through Yosemite Valley - moved generally east to west. There were glaciers in the south during the ice ages which were not there before because as the Earth became colder on average, the area where snow and ice could remain unmelted through an entire summer spread to encompass more southerly areas. Was that what you meant to ask? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [August 25, 2006, 9:55pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/5 "2006-08-25T21:55:53Z")
Looking at some of the giant glacier moved boulders around my area, I have wondered this too. Wasn’t just one giant layer of snow and ice? Obviously not but I would expect things to basically melt in place with only some movement. Good question. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [August 25, 2006, 9:56pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/6 "2006-08-25T21:56:58Z")
I think the OP is asking why did the glaciers appear further south than they currently do. If I am correct, then the answer is “weather”. Glaciers form when a huge amount of snow falls onto a mountaintop, compacts, and flows down the side of the mountain. When it’s colder further south, then more snow falls on peaks further south than we would expect, and glaciers form. ---
**Author:** ![Baffle](https://avatars.discourse-cdn.com/v4/letter/b/dec6dc/32.png) [@Baffle](https://boards.straightdope.com/u/Baffle)\ **Post date:** [August 25, 2006, 9:59pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/7 "2006-08-25T21:59:05Z")
Hills? You think a glacier is going to be stopped by mere _hills_? Glaciers scour the land behind them flat and either push hills out of their way, or meltwater erodes through them when summer comes. Remember that glaciers would advance and recede with seasonal fluctuations in temperature – yearly flow rate is an average of all movement. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [August 25, 2006, 10:00pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/8 "2006-08-25T22:00:15Z")
[QUOTE=wevets] I’m not sure all glaciers moved north to south - the ones I’m most familiar with, which plowed through Yosemite Valley - moved generally east to west. There were glaciers in the south during the ice ages which were not there before because as the Earth became colder on average, the area where snow and ice could remain unmelted through an entire summer spread to encompass more southerly areas. Was that what you meant to ask? [/QUOTE] I actually deleted half my OP to shorten it. This week I learned that the Canadian Shield has no soil because the glaciers scraped it clean and deposited it further south. There are not a lot of mountains around here so what force pushed these glaciers? ---
**Author:** ![Baffle](https://avatars.discourse-cdn.com/v4/letter/b/dec6dc/32.png) [@Baffle](https://boards.straightdope.com/u/Baffle)\ **Post date:** [August 25, 2006, 10:02pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/9 "2006-08-25T22:02:04Z")
[QUOTE=Baffle] Hills? You think a glacier is going to be stopped by mere _hills_? Glaciers scour the land behind them flat and either push hills out of their way, or meltwater erodes through them when summer comes. Remember that glaciers would advance and recede with seasonal fluctuations in temperature – yearly flow rate is an average of all movement. [/QUOTE] Now to answer the real question… cough Glaciers I’m familiar with (southern Ontario) had no place to go east, west, or north (there was already frozen ice there that wasn’t moving) and they had to flow somewhere as pressure from more snowfall built up on the ice itself. They flowed south, pushing any hills out of the way through the mechanisms described above. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [August 25, 2006, 10:05pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/10 "2006-08-25T22:05:15Z")
[QUOTE=solkoe] I agree that land is rarely flat. And this sounds good if the thousands of kilometers of travel were all downhill. Didn’t they have to go uphill too? [/QUOTE] If you keep piling up sand in a single location, it will spread out. The ice kept forming in the furthest northern places, building up higher. The weight of that ice pushed it to spread out, eventually spreading further away from the point of origin. This would cause the ice sheets to move south in this case. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 25, 2006, 10:08pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/11 "2006-08-25T22:08:05Z")
Even ice has an [angle of repose](http://en.wikipedia.org/wiki/Angle_of_repose). If it snows enough to create a pile two miles high in the center of a perfectly flat plane, the stuff will flow until it is flat enough to support itself. No underlying hill is needed when the scale is large enough. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [August 25, 2006, 10:11pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/12 "2006-08-25T22:11:54Z")
Some of the answers here don’t make sense, particularly **Telemark** ’s. Glaciers aren’t necessarily contiguous. It wasn’t like there was one gigantic glacier that appeared in the north of the world and moved south - they appear wherever the conditions are right for formation. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 25, 2006, 10:17pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/13 "2006-08-25T22:17:07Z")
[QUOTE=jjimm] It wasn’t like there was one gigantic glacier that appeared in the north of the world and moved south… [/QUOTE] [Laurentide ice sheet](http://en.wikipedia.org/wiki/Laurentide_ice_sheet) > [@](#): > > The Laurentide ice sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, between ~90,000 and ~18,000 years before the present day. Its southern margin included the modern sites of New York City and Chicago, and then followed quite precisely the present course of the Missouri River up to the northern slopes of the Cypress Hills, beyond which it merged with the Cordilleran Ice Sheet. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 25, 2006, 10:28pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/14 "2006-08-25T22:28:09Z")
Like **Telemark** [said](http://jove.geol.niu.edu/faculty/fischer/429_info/429trips/NIF/Glaciers.htm): > [@](#): > > With enough snow accumulation and time, pressure from overlying snow may be build up enough to convert firn into crystalline ice and cause flow. Ice under sufficient pressure behaves plastically and deforms under its own weight at the crystal level. However, the upper 40 meters of ice behaves rigidly, riding on ice layers behaving plastically beneath. Valley glaciers flow plastically and by basal sliding. **Continental glaciers usually remain attached at its base to the substrate, moving plastically, downward and outward from a central high area toward its margins** (see Figure, Plummer,1999). In both, snow and ice accumulation causes a transfer of mass thru the ice and results in glacier advancement. NB: bolding added ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [August 25, 2006, 11:57pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/15 "2006-08-25T23:57:43Z")
Oh, ok then. ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [August 26, 2006, 6:14pm UTC](https://boards.straightdope.com/t/what-force-moved-the-glaciers/370254/16 "2006-08-26T18:14:44Z")
I can’t follow the above link for some reason, but a related phenomenon that has always intrigued me is [Isostasy](http://gemini.oscs.montana.edu/~geol445/hyperglac/isostasy1/) . Parts of the world are very slowly twanging back into place after having been mashed down hundreds of metres under the weight of millions of tons of ice. Particularly noticeable in the Baltic. Gives you a feel for just how much ice built up…