Have you ever tossed a plastic bottle full of water into the freezer?  When you opened the freezer a few hours later, you might have found a big mess.  The bottle had broken.  Water leaked everywhere and froze.  Ice is pretty powerful stuff.  It can rip apart plastic.  It can break rock, just like wind and water.
 
Bump-bump.  When your bicycle tire hits a pothole in the road, you get a first-hand look at how ice can break rock.  Rain or melted snow soak into small cracks or holes in the road.  When it gets freezing cold at night, that water becomes ice.  Then it's just like what happened to the bottle in your freezer.  The ice expands and takes up more space than the water did, breaking the road apart.  The next day, as the road warms up, the ice melts and creeps deeper into the cracks, only to turn back to ice when it gets cold again.  Freeze-thaw is when water becomes ice as the temperatures dip below freezing, then turns to water again as the day heats up and repeats this over and over.  

It may take a few days for this road to thaw out.


In some parts of the world, it is cold or freezing all year around.  The snow does not melt much, so it builds up over time.  This snow becomes heavier and heavier, pushing down on the layers of snow on the bottom.  Think about what happens when you forget about that banana in your bag and put your books on top of it.  Squish!  The same thing happens with the snow.  The snow on the bottom gets so squished that it turns to ice.  Glaciers are slow moving rivers of ice formed from years of snow build up.  They flow like slow rivers, but move so slow that you cannot see it.

Anyone need some ice for their water container? Just go find the nearest glacier.


Glaciers are like big bulldozers.  They have a lot of power to change the shape of the land.  This is because they are made up of more than just snow and ice.  At the bottom of the ice sheet, there are rocks that have been frozen into it.  This makes the ice like the roughest sandpaper you have ever seen.  When the ice flows down the hill, those rocks in the ice grind away at the rock under the ground, just like sandpaper grinds and smooths rough wood.  Abrasion is when something grinds away at something else.  The glacier rubbing against the ground is an example of very strong abrasion.  

A glacier crushed and pushed all the rock out of it's way.


When glaciers flow downhill, they often follow the zigzag paths that streams have carved.  Most valleys made by streams look like the letter V.  That is because the water only wears down at the bottom of the valley, where the water is flowing.  Ice works in a different way.  Instead of just pushing dirt from the bottom of the valley, the ice grinds against the sides too.  It works more like a spoon.  It scoops out the valley, making it look like the letter U.  U-shaped valleys are valleys shaped by glaciers with steep sides and wide bases.
 
Here's a glacier making a valley for itself.


Ice is powerful stuff.  It can burst your water bottle.  It can break up the road.  Great flowing ice sheets can grind up the land.  In the battle of rock versus ice, ice wins, hands down.

References:

"All About Glaciers." National Snow and Ice Data Center, 2013. <https://nsidc.org/cryosphere/glaciers>

Ferguson, William. "Ice Core Data Help Solve a Global Warming Mystery." Scientific American, March 2013. <http://www.scientificamerican.com/article/ice-core-data-help-solve/>

"Glacier." UXL Encyclopedia of Science. U*X*L, 2001. Science In Context.  <http://ic.galegroup.com/ic/scic/ReferenceDetailsPage/ReferenceDetailsWindow?failOverType=&query=&prodId=SCIC&windowstate=normal&contentModules=&display-query=&mode=view&displayGroupName=Reference&limiter=&currPage=&disableHighlighting=false&displayGroups=&sortBy=&search_within_results=&p=SCIC&action=e&catId=&activityType=&scanId=&documentId=GALE%7CEJ2644300497&source=Bookmark&u=k12_science&jsid=b81adb61d4e759b38e093fd822373042 >

"Global Sea Level." NASA, July 2013. <http://www.nasa.gov/topics/earth/features/pia16294.html#.U8mwLLFeZzc>

"Sea Level" NASA Climate Kids, 2013  <http://climatekids.nasa.gov/health-report-sea-level/>

"Sea Level Rise: Ocean Levels Are Getting Higher -- Can We Do Anything About It?" The Ocean. National Geographic, 2013. <http://ocean.nationalgeographic.com/ocean/critical-issues-sea-level-rise/>