# Part 4—Find Glaciers on the Go

## Step 1 – Explore Greenland's Glacier Velocity Gates Layer

Scientists are interested in understanding the Mass Balance of Greenland's ice sheet. They want to check if the amount of new snow falling on the ice sheet each year is more than, equal to, or less than the amount of ice that is sliding off of the continent. If the amount of new snow is equal to the amount of ice lost, the mass of ice on the continent will remain stable, and nothing will change. However, if the amount of ice being lost is greater than the amount of new ice, there is a net movement of fresh water from the land into the ocean, and global sea levels will rise.
1. In Visualize mode, turn the following layers on. Leave all other layers off.
• Continents
• Greenland Glacier Velocity Gates
• Greenland Ice Sheet
2. Use the Zoom In tool to zoom in on the line of dots representing Glacier Velocity Gates.
3. Use the Measure tool to check the distance between several successive pairs of "gates." To make a measurement, click on the Measure tool icon to select it (it will turn grey). Then move to the map where the crosshair cursor can be placed on any gate and click once to start measuring. Then move to an adjacent gate (a line will draw) and click twice. The distance, in meters, appears on the lower left information bar of the My World window.
• What is the average distance between these points?
4. Note that the points are generally parallel to Greenland's coast, indicating that they are all roughly at the same elevation.
• How do you think this line of points might be used in measuring the downhill velocity of Greenland's ice? Describe your ideas to a lab partner.
• Once you've thought about it and described your idea, check the "Show me" link below to see if your ideas are similar to the ones scientists used.

## Step 2 – Check the Data from the Velocity Gates

1. Activate the Greenland Glacier Velocity Gates layer by clicking its name in the Layer List, then click the table icon to open its data table.
2. Each row of data (also known as a record) provides information for one of the 161 gate points. Sort the records by clicking the Elevation header to find the range of elevations for the gates.
3. Sort by the Velocity (m/year) column to find the fastest and slowest downhill velocities of the ice.

## Step 3 – Discover which Regions of the Ice Sheet are Moving most Rapidly

1. Activate the Glacier Velocity Gates layer, then choose Layer &gt; Edit Layer Appearance, to open the Legend Editor.
2. In the Legend Editor, click the Color tab, then select the "Choose Color by" drop-down menu and select Velocity (m/year).
3. Check the results on your map, noting any visible patterns that reveal areas of fast or slow movement of the ice.
4. Turn off the Greenland Ice sheet layer in order to see the full range of colors of the gates.
5. Experiment with other legend options to display the velocity gates data in new ways. For instance, you may want to show velocity using dots of different sizes, or use an arrow to indicate the bearing (direction) of the flow.
6. Use Analyze mode to highlight gates where the average velocity of the ice is is greater than 80 m/yr.
• In Analyze mode, choose Select &gt; By Value... to open the dialog box.
• Select records from Greenland Glacier Velocity Gates whose Velocity (m/year) is Greater than or equal to (&gt;=) a value of 80.
• Click OK then accept the default name by clicking OK again.
• On your map, choose a highlight mode that will allow you to see your selection that shows the fastest moving ice.
• Glacial meltwater in Greenland. Image source: NASA Earth Observatory.

• Observe your map with the selections, and answer the following questions:
• Is there a pattern to where the fastest moving glaciers are located? How might this be related to weather and climate patterns?
• If the glaciers in southern Greenland are melting, where does the melt water go? How might this fresh water impact the ocean?
• Finish this chapter by skimming through the article, and viewing the slide show, from National Geographic entitled "The Big Thaw". For more information about the Greenland Ice Sheet, visit the links listed in the Going Further section of this chapter.