EarthLabs > Climate and the Cryosphere > Lab 3: Land Ice > 3A: Mass Balance

Land Ice

Part A: Mass Balance

The term "land ice" can be used to describe any ice that formed over land primarily from freezing precipitation (as opposed to sea ice, which forms by the freezing of seawater). This includes glaciers, ice sheets, ice shelves, icebergs, and frozen ground. Read this excerpt about land ice (Acrobat (PDF) 305kB Jul2 11) from the NSIDC page "All About the Cryosphere" to familiarize yourself with the different types of land ice or click here to read the full article. In this part of the lab, we'll be focusing on glaciers.

Diagram of a glacier showing components of mass balance. Image source: USGS.
Glaciers can form anywhere that snow and ice remain year-round. They grow slowly over thousands of years, as snow is compacted into ice by the weight of subsequent snowfalls. The key to a glacier's survival depends on the relative amounts of accumulationaccumulation: processes by which snow and ice are added to a glacier. and ablationablation: processes (melting, evaporation, sublimation) by which snow and ice are removed from the surface of a glacier. the glacier experiences. If accumulation is greater than ablation, the glacier has a positive mass balancemass balance: the difference between accumulation and ablation. is positive and the glacier grows in size. If ablation outpaces accumulation, mass balance is negative and a glacier shrinks. If the two processes result in no net gain or loss of snow and ice, the mass balance is zero and the glacier is in equilibriumequilibrium: a balanced state with no net gain or loss..

Scientists are interested in studying these thermodynamic processes in glaciers because of the potential impacts for both humans and wildlife. More than two billion people around the world (primarily in China, India, Pakistan, and Bolivia) rely on glacial melt water for drinking and agriculture, but if glaciers melt too fast, there can be catastrophic flooding followed by a fresh water shortage. Melting ice sheets could result in loss of habitat for many species of birds and mammals, rising sea level, and increased global warming.

In this part of the investigation, you will explore glacial accumulation and ablation processes using parts of an online interactive produced by the University of Kentucky. By studying these processes, scientists are able to determine whether a glacier is growing or shrinking and whether changes in the glacier's mass balance are related to climate change.

  1. Read the Introduction text on the Home page of the interactive.
  2. Click on the Overview button. Then use the right arrow (->) at the top right of the interactive window to go to page 2: Anatomy of Glaciers.
  3. Study the animation carefully and read the accompanying text in the column on the right. At the bottom of the text column, click on the right arrow (->) to get additional information about the animation.
  4. Click on the Model button. Follow the instructions in the column on the right for using the model to adjust the climatic factors that cause glaciers to grow or shrink. At the bottom of the text column, click on the right arrow (->) to get additional information.

  5. This content is available in flash format only

    Developed by the University of Kentucky College of Arts & Sciences Earth & Environmental Sciences Educational Materials.
    Used with permission.
This interactive is not included in the EarthLabs iPad app. To view it, please use a Flash-enabled device.

    Checking In

    1. The area of a glacier that receives more snow than can melt is called the:
      [INCORRECT] Oops! Ablation is a fancy word for loss. The Ablation Zone is actually the part of a glacier that's losing mass through melting and other processes.
      [INCORRECT] SorryTry Again! The terminus is the downhill end of the glacierthe line scientists use to determine whether a glacier is advancing or retreating.
    2. Which of the following is NOT a primary process of mass loss (ablation) observed in glaciers?
      [CORRECT] That's right! A receding terminus isn't a process of ablation, it's a result of ablation. A receding terminus doesn't extend as far as it did the previous year. In other words, the glacier is shrinking.
    3. What do scientists use the "line of equilibrium" to determine?
      [CORRECT]Great job!

    Stop and Think

    1: Explain what it means for a glacier to be in equilibrium.

    2: What evidence could scientists use to show whether or not a glacier is in equilibrium?

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