Erosion by Glaciers

Section 1

Daily Dose of Destruction

glacier calving video.jpg

Glaciers are large masses of moving ice and snow.  Don't confuse them with icebergs.  Icebergs were once part of glaciers, but have broken off and are floating on water body.  Glaciers are formed when snow doesn't melt all the way and begins to pile up.  The heavy snow layers on top compress and compact the snow below.  If you have ever been in a snowball fight you probably have experimented with this process.  You take some snow in your hand, squeeze and compress it, the snow heats a little and the interlocking crystals move closer together forming ice or harder snow.  Same happens to the layers below the top when there is enough friction that it slightly melts the lower layers making those ice crystals move closer together and harden as the water refreezes into ice.  The bottom of a glacier becomes a little pliable, sort of like silly putty.  This allows it to move downhill due to the force of gravity.

 

glacier

Glacier

 

iceberg

Iceberg

 

There are two types of glaciers, continental and alpine.  Continental glaciers are huge masses of ice and cover large areas of land.  During the ice ages, the Earth might have been 28% covered with glaciers.  There have been many ice ages, but the last one occurred about 2 or 3 million years ago.  Glaciers still cover about 10% of the Earth.  These glaciers were so large that they covered mountains and carved out some fantastic valleys that we have turned into national parks like Yosemite.Continental glaciers can be so large that they weigh enough to push some of the crust into the mantle.  After the glacier melts the land goes through what is known as post-glacial rebound, where the land begins to rise up out of the mantle.  There is a village called Alby, in Sweden, that due to this post-glacial rebound it is no longer the fishing village it used to be.  As Alby began to rise the sea began to move away from the village.

Alpine glaciers are smaller glaciers that carved out some of these mountains and valleys.  There are just a few alpine glaciers left.  There are some beautiful landmarks, landforms, and landscapes that have been sculpted by these alpine glaciers.  

 

continental glacier

Continental Glacier

 

 

Alpine Glacier

Alpine Glacier

As glaciers move down slope, sometimes they will "pluck" up rocks from below and begin to drag those rocks.  The dragging rocks scratch deep grooves into the rock below.  The scratches are called glacial grooves.

 

Glacial Plucking

Plucking

 

 

Glacier Grooves

Glacier Grooves

Below is a slideshow that demonstrates some of the awesome, majestic landscapes that have been formed by glaciers.

In the following lab, you will become a scientist and discover how glaciers grow, shrink and move as well as calculate the rate of speed that your created glacier is moving over time. 

SUSD5 student version of the Phet Glacier Lab.

Purchase a copy of the Phet Glacier Lab at Teacher Pay Teachers for 0.80 cents.

Section 2

Daily Dose of Destruction

glacier calving and wave video.jpg

We have already mentioned that glaciers and ice weather rock and then move that rock to another location.  When the glacier runs out of energy or melts it deposits it's load.  This next section will deal with glacial deposition.  The mixture of different sized sediments that were moved by the glacier is called till.  If you ever come across a hill that is made out of till you would call that a drumlin.  If you lay a spoon upside down on a table and look at the spoon part, not the handle, you are looking at the shape of a drumlin.  Where you find one drumlin, you probably will find more as they are often found in what is known as a drumlin field.  The direction the drumlin is pointing is the direction the glacier was moving at the time of it's formation.

 

Till

Till

 

 

Drumlin

Drumlin Hill

 

Moraines are glacier deposits that form at the edges of the glacier.  The moraines found at the farthest point the glacier has ever reached are called terminal moraines.  A moraine that is pinched between two glaciers is called the medial moraine, similar to the word median which is middle barrier between parts of highways.  Lateral moraines are the moraines that are found at the outer edges of glaciers.

moraines

If you are walking in the wilderness and come across a rock or rocks that clearly do not belong in the area, then you might be looking at an erratic.  Erratics are carried long distances on top or inside of a glacier.  When the glacier melts it deposits this erratic.  It literally is a rock that just does not fit into its surroundings.  Erratics can be dropped into the middle of the ocean by icebergs and then when the ocean sediment turns to rock it will include this erratic.  So if you are ever looking at limestone and then notice a big chunk of sandstone in the middle of it, you might be looking at an erratic.

 

Glacial Erratic

Glacial Erratic

An outwash plain is the glacial till that is deposited by the glacier's melted runoff.  You will find outwash plains at the base of glaciers, usually accompanied by rivers and near ocean shores.

outwashplain

We are going to watch "Chasing Ice," a video where a photographer has gone out over the years taking thousands of pictures of glaciers, glacier calving, glacier receding.  Although this video is politically motivated, you can take it for what it is worth.  The purpose of the video is to see all the different landforms, landscapes, and deposits that glaciers make.  If you watch it for that reason, you will like the video.

chasing ice video.jpg