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In Learn More the National Geographic magazine team shares some of its best sources and other information to expand your knowledge of our featured subjects. Special thanks to the Research Division.
The Big Thaw
By Emily Krieger, National Geographic Staff

Did You Know?

People who live in or study the Earth’s cold places have many different words to describe various types of ice and snow. In many cases, size determines the definition. For example, an ice sheet has a domed shape and covers more than 19,300 square miles (50,000 square kilometers), while an ice cap, also domed, is smaller than 50,000 square kilometers. Because they flow, glaciers are sloped and generally smaller than ice caps. In other cases, age and structure determine the definition. New snow must not only be recent but must preserve the original form of the snow crystals. Névé is young snow that has partially melted, refrozen, and been compacted. Névé that lasts a full season is referred to as firn. Over many years, firn can become compacted into ice.

Related Links


  • Allaby, Michael. The Concise Oxford Dictionary of Ecology. Oxford University Press, 1994.
  • McGonigal, David, and Lynn Woodworth. Antarctica and the Arctic: The Complete Encyclopedia. Firefly Books, 2001.

NGS Resources

  • Glasener, Erica, and others. “The Green Guide #119.” National Geographic’s The Green Guide (March/April 2007), 1-12.
  • Bennett, Paul. “Greenland When It’s Hot.” National Geographic Adventure (November 2006), 93-103, 109-10.
  • Zwingle, Erla. “Meltdown: The Alps Under Pressure.” National Geographic (February 2006), 96-115.
  • Botkin, Daniel B., and others. Forces of Change: A New View of Nature. National Geographic Books, 2006.
  • Phelan, Glen. “Melting Away.” National Geographic Explorer! (January/February 2005), 4-11.
  • Morell, Virginia. “TimeSigns: Now What?National Geographic (September 2004), 56-75.
  • Montaigne, Fen. “EcoSigns: No Room to Run.” National Geographic (September 2004), 34-55.
  • Glick, Daniel. “GeoSigns: The Big Thaw.” National Geographic (September 2004), 12-33.
  • Johnson, Rebecca. Global Warming. National Geographic Books, 2002.