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.

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. Mass balance, the difference between accumulation (processes by which snow and ice are added to a glacier) and ablation (processes by which snow and ice are removed from the surface of a glacier), is the key to the survival of a glacier. If accumulation is greater than ablation, mass balance 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 equilibrium.

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 an online interactive produced by ThinkTV. 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. Roll over each icon on the glacier in the interactive below to learn about the clues scientists look for to determine whether glaciers are experiencing possible climate-driven changes. Click on the icons to reveal additional information.
   
   
   Courtesy Teachers Domain.
   
   
   

   Checking In

   The area of a glacier that receives more snow than can melt is called the:
   Ablation Zone 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.
   
   Accumulation Zone
   
   Terminus Sorry—Try Again! The terminus is the downhill end of the glacier—the line scientists use to determine whether a glacier is advancing or retreating.
   
   Which of the following is NOT a primary process of mass loss (ablation) observed in glaciers?
   melting
   
   calving
   
   receding terminus 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.
   
   evaporation
   
   sublimation
   
   What do scientists use the "line of equilibrium" to determine?
   which parts of a glacier are gaining or losing mass Great job!
   
   the age of a glacier
   
   how fast a glacier is moving
   
   how much a glacier weighs
   
   
   

   Stop and Think

   
   

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

   2: Describe how scientists determine glacial mass balance.