How glaciers are formed

Glaciers are great ice rivers, made of snow falling on the highest parts, and descending by means of gravity and its own weight.

The main condition for a considerable mass to form is the amount of snow, which must be higher than the amount melting; and temperature must be low to allow the storage of that snow.

Snow becomes compressed at its contact to earth, and the crystals start losing their shape, melting against each other. During this process, the air separating the flakes at the beginning is set free. The weight of the new snow layers compresses the crystals, by these means diminishing the amount of air, until it almost disappears.

The time this process takes depends on the amount of snow that has fallen in the area, and the temperature, being it shorter when the area's climate is warmer (e.g., in the National Park). This occurs because a higher temperature produces melting on the glacier's area, the liquid flows through the lower layers, and when it freezes again, it covers the air spaces left behind, giving this process a higher firmness.

What makes them so beautiful

The slopes the glaciers find in their way make gravity act giving them different shapes.

The main condition for their sliding is that the glaciers must be over water, and this is only possible in warm places, as in our National Park, because of its highest layers' melting, and because the highest temperature occurs in its rocky base.

The speed at which a glacier moves depends on three different things: its width (always higher than 20m), its slope and ice temperature. This feature is the one which most varies among the glaciers, as these conditions do not occur repeatedly in every case.

Another influence factor are the different movements and friction between the glacier and its bed, making movement speed faster in its area than at its bottom part, and against the valley's sides, which make speed faster at the centre than at its sides.

Another thing we can observe are moraines, formed by earth and stone accumulation, which are carried by the glacier, keeping them together at a certain place, only as Nature's whim. They are generally formed on the glacier's banks, although in many cases where glaciers meet, they are formed at the very centre of that junction.

Another attraction is cracks. These are formed by the different pressure points, and changes in speed made when ice blocks move, combined with ice's higher or lower elasticity, and because compression is not always the same.

The best-known glaciers

Perito Moreno Glacier

Besides being the most visited one, as it s the only one you can reach by land, its main feature are its ruptures, and breaking off of small blocks, and sometimes important walls. This occurs because the front wall is not deep enough, making a strong push between its pressure to go forth and the one stopping it at the base.

The Rupture: The great ruptures phenomenon is reached when the front part of the glacier reaches Magallanes Peninsula (under the area of the pasarelas). It forms a natural dam, which makes the water in the southern branch of Argentino Lake generate a higher pressure on the dam, as its level rises, fed by thaw in that area. When the difference in water level between both parts is considerable (between 9 and 30 m), the dam starts breaking off, water flows and leaves its race until forming a bridge between the glacier and the peninsula, which finally breaks down. We cannot predict this phenomenon, as the glacier has no movement standards.

Upsala Glacier

You can only reach this glacier by ship, as it is located in the northern branch of Argentino Lake. Its main feature, besides its size (it's many times bigger than Moreno), is the size of the icebergs breaking off from its front wall. They are huge blocks, generally bigger than the ships that take you to the area. This happens, as experts say, because its front wall is deeper than Moreno's, and the amount of water in its base must be higher (we don't know exactly, but it is thought that it floats), showing a lower pressure as it moves. It's very difficult to see a rupture in this glacier, but sailing between its icebergs is a fascinating experience!

Moreno Glacier's Ruptures

1899     First observations.
1903     Its front wall reaches 750m from the peninsula.
1908     Its front wall reaches 350m from the peninsula.
1914     Its front wall reaches 100m from the peninsula.
1917     It reaches the coast, forming a dam.
1928     It moves 150m away from the coast.
1934/35     the dam is formed again.
1936     The bridge in the dam breaks off.
1937     It starts moving forth towards the peninsula.
1939     Water level in Rico branch rises.
1941     Water level in Rico branch: 7.42m   
1942     Water level in Rico branch: 17m.    
1952     Rupture process starts again.

1953     It closes again before a year from its last rupture has passed.
1956     Another rupture occurs.
1966     Water level in Rico branch: 32m.
1970     Another rupture occurs.
1972     Another rupture occurs.
1976     Another rupture occurs.
1980     Another rupture occurs.
1984     Another rupture occurs.

1988     Another rupture occurs.

2003     The dam is formed in October.
2004     Rupture occurs on March, 25st.

Source:
Los Glaciares National Park Administration,
Manual del Lago Argentino by Miguel Angel Alonso.