The Story of Glaciers
Excerpts from Icebergs. Christian Kempf.
From Snowflake to Ice Caps to Glaciers*
Snow gathers in hollows called “cirques,” sometimes up to 20 to 30 meters deep, (65 - 98 ft) assisted by wind, rain and avalanches.
Fallen snow packs down and becomes less complex in structure as it releases much of the air that was trapped inside between the individual flakes. This granular snow turns into ice over several years as the crystals bond to each other under high pressure, reaching ever larger sizes, that then bond to each other in turn.
It generally takes five to ten years for snow to turn to ice. In Greenland or Antarctica, this process can take a hundred years, while it takes just three to five years on certain glaciers in Svalbard or the Alps, where there is greater snowfall and the climate is cooler – speeding up the process.
Glaciers are formed from successive layers of snow, though freezing mist or surface meltwater can also cause the ice to build up. These accumulations of ice in the center of continents and polar islands are called ice caps (up to 50,000 km2) or ice sheets (over 50,000 km2) (19,305 sq mi).
The ice is up to 600 meters deep in Svalbard and the Campo do Hielo, Chile, (1968 ft). 3100 meters in Greenland (10,170 ft) and up to 4800 meters in Antarctica (15,748 ft or 3 miles deep).
The ice builds up until it overflows the depression where it has accumulated. The glacier then begins to flow downhill, and a long story starts.
Year on year, the polar ice caps trap pollen, volcanic ash, dust and pollutants in regular strata, so crating one of the best indicators of the state of the environment. The thickness of these strata varies from one to ten centimeters a year, but these “archives” of planet Earth go back over 740,000 years.
By drilling into the ice, we find traces of tree pollen from 5000 years ago, and volcanic dust from Mount Merapi in Indonesia – which underwent a huge eruption 18,000 years ago. In our own era, we can trace the build-up of lead and carbon dioxide since the 1930’s, a result of industrial growth and increased use of the motor car.
Weight and gravity cause this ice to flow at speeds of several meters a day through narrow valleys between the nunataks – jagged peaks caused by alternate freezing and thawing.
The crystals and air trapped in the ice facilitate the flow of this powerful river that erodes and gouges, breaking into crevasses and seracs.
The glacier melts and water runs off in glacial rills, mills and sumps, while the friction between these billions of tons of ice, and the rock, causes the underside of the glacier to melt too, allowing it to slide on a very thin bed of water, which also crates sub-glacier rivers.
The glacier flows slowly to the sea, until the ice front ends up hanging over the water, unsupported. When the stress becomes too great, it breaks off, sending millions of tons of ice crashing into the sea. And so, icebergs are born.
THE MAJOR ICE CAPS/SHEETS AND GLACIERS
Antarctic Ice Sheet 13,586,000 km2 5,245,584 sq mi
Greenland Ice Sheet 1,710,000 km2 660,235 sq mi
Rocky Mts (Canada&Alaska) 60,000 km2 23,166 sq mi
* Icebergs. Christian Kempf. Les Éditions de l'Escargot Savant. Le Thillot 21230 Viévy France. 2014 pp 19-23.