Glacier in the Rocky Mountains – Definitions & Diagram

A glacier slowly winding its way down a valley.

Glaciers play a huge role in shaping the landscape of the Rocky Mountains.  Here is a definition and a diagram showing evidence of glaciers in the andscape.

Personally, I’ve always been kind of fascinated by glaciers.  I mean, they are these huge (really, really, really big) masses of ice that cover the landscape.  There are some smaller ones, but many others are just humongous.  I think one of the other reasons I’m enamored with them is because they are often located in alpine areas (which I love).  These huge masses of ice have shaped and are still shaping the rugged landscape of the Rocky Mountains.   Here are some basic terms that show how they have shaped the landscape.

What Is A Glacier?

DEFINITION –  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 beautiful U-shaped valley is clear evidence of glaciers.

There’s Evidence Of Glaciers In The Landscape If You Know What To Look For

The 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.

Image courtesy of Jake’s Nature Guide: Rocky Mountains.

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.

A tarn (Lake Summit) in a cirque below Mt. Evans in Colorado. Photo via Flickr.

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.

A glacial erratic. Photo via Flickr.

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.

Look at that beautiful turquoise water.

Turquoise 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.

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