Glaciers in the Rocky Mountains

rocks active glacier in valleyThe landscape of the Rocky Mountains amazes visitors with its beauty – the towering peaks, crystal clear streams, and meadows full of wildflowers.  This landscape was formed and shaped by many forces, including water, wind, fire, and importantly glaciers.

Glaciers have had an enormous impact on shaping the landscape in some areas of the Rockies.

I have been lucky enough to explore some areas of the Rockies that still have glaciers present year round, such as in many areas around Glacier National Park in Montana and have been impressed with the enormity and power of these giant, silent sheets of ice.  Even after hiking a couple of hours up into the mountains to arrive at a small lake and look up at a glacier that makes its way down from the top of the mountain to drain into the lake it is hard to fully understand how the ice can shape the landscape.

What exactly is a glacier?dog 14

DEFINITION OF GLACIER –  A glacier is a slowly moving mass or river of ice that formed by the accumulation of snow over time.

This means that a glacier is not simply a snow field.  Rather, a glacier is like a large ice cube that gets added onto every winter and is slowly sliding downhill.


  • A glacier does not melt during the summer.
  • As more snow is added to the top of the glacier, the total snow gets heavier, which creates more pressure on the bottom parts and turn it into ice.
  • The glacier slowly moves down a mountain and scrapes along the surface, forming a valley.
  • Large boulders can be frozen inside of a glacier and carried many miles before they are dropped, either out the bottom or end of the glacier as it melts.
  • Glaciers cover about 10% of the earth’s surface.

As I said earlier, I have visited and seen glaciers for myself.  So, this means that there are still many places where glaciers are changing the landscape.  However, in most cases the glaciers of the past have completely melted away.  Despite this, the evidence of glaciers can still be seen in the landscape if you know what to look for.

rocks glacial valley with stream U shapedThe most telling sign of glaciers is a large U-shaped valley.  In mountains, rivers flow downhill and carve out a v-shaped valley.    However, when glaciers flow down these same valleys, they change the landscape.  As the glaciers move down the valley they scrape away the sides to make it more rounded and wider than it was previously.  Doing so creates a large U-shaped valley.

Here is a diagram that shows the evidence of glaciers in the landscape.

glacial landscape

Other than the big U-shaped valley there are many other signs of the evidence of glaciers in the landscape.  Some of these are shown on the diagram and here is what they are:

Moraines – Glaciers contain lots of rocks that either fell onto the glacier or were picked up by it. When the glacier melts these are dropped and form a ridge of glacial debris. These are called moraines.  The glacier is melting both at the lowest or most downhill point of the glacier and along the sides.  The mound or ridge formed by the debris that collects at the end of the glacier is called a terminal or end moraine.  The debris that is dropped and deposited on the sides of the glacier is called a lateral moraine.

Cirque – A bowl shaped depression at the head of a glacial valley with tall walls on three sides and open down the valley.  This is where the glacier begins and the snow accumulates.  Rivers have headwaters where they begin and the cirque is like the headwaters for a glacier.

Tarn – A small lake in a cirque that is created by the glacier.

Hanging Valley – When the glaciers get smaller or disappear the valleys of the tributaries are higher up and are termed hanging valleys.

Pater Noster Lakes – A string of lakes going up a glacial valley.

Truncated Spur – As the glacier flows around sharp curves in a valley it erodes away the sharpness and creates triangular shaped cliffs.

Arete – A steep sided, sharp edged ridge that is formed by two glaciers eroding the mountain on opposite sides of the ridge.

Erratics – This is a rock or boulder that is a different kind of rock than the rocks upon which it is sitting.  These rocks or boulders are picked up by a glacier and moved by it before dropping it in a different location.

Glacial Striation – These are long scratches and grooves in otherwise smooth rocks. Rocks stuck in the glacier gouged these lines in the bedrock as the glacier moved along over it.

rocks glacial river aquamarineTurquoise Water – The water in lakes, or streams whose water comes from glaciers acquires a brilliant turquoise color. This happens because as the glacier moves it picks up fine particles of rocks. When it melts this ‘rock flour’ goes into the water and the sunlight refracting off the particles in the water creates this color.