Antarctic Mysteries

Section

Flow Stripes

flowstripes
Flow stripes (taken from the LIMA flyover video)
As the ice deforms and begins to flow over the rough surface below it, bumps form on the surface of the ice that stretch out as the ice moves and form a series of ridges and troughs in the ice that we call flow stripes. Flow stripes provide a convenient record that scientists can analyze to determine the past flow pattern. If the flow stripes do not align with the current flow direction, it is an indicator of a change in the flow pattern over time. Flow stripes can be difficult to detect, however, so scientists often have to enhance the images to see them clearly—see example below. The direction of the sun’s illumination of the ice sheet when the image is obtained also plays an important role, making it easier to see some stripes and more difficult to see others. Scientists can analyze satellite data to determine which way the ice is flowing and to tell where ice anywhere on the ice sheet came from and where it is going.

Two glaciers
Large size image (new window)
This dramatic image shows the massive and fast-moving Byrd Glacier (upper right) as it roars down the East Antrarctic Ice Sheet toward the Ross Ice Shelf from the northeast, while at the same time the smaller and slower-moving Mullock Glacier approaches the Ross Ice Shelf from the southeast. The two glaciers are on a collision course towards one another! What will happen when they meet?

Perhaps flowstripes can give us a clue...

When we look at the original image, we don’t learn all that much at first glance. We can see that there are flow stripes in each glacier, but they seem to fade away before the glaciers meet. As the two glaciers come together, it becomes harder and harder to make out the individual flow stripes from each glacier with our eyes, because the ridges and troughs slowly merge together, and make the differences harder to see.

But sometimes there is more to an image than meets the eyes. Scientists have developed a technique called contrast stretching that allows them to see details contained in the digital image that would otherwise be invisible to our eyes. Contrast stretching works exactly the same as what happens when we adjust the contrast on our television and helps to bring out more detail in a particular region of interest. The surrounding regions that are already bright become even brighter and the regions that are dark become even darker. We sacrifice detail in these other areas so we can see the area where the glaciers are colliding—called the collision zone—in more detail.

The series of images shown below illustrates contrast stetching. The button on the far left shows the original image, and each successive “stretch” reveals more and more detail around the collision zone. Notice how the flowstripes become more and more apparent with each successive “stretch”. We now can begin to answer the question of what will happen when Byrd Glacier and Mullock Glacier collide together.

| | | | | 5

We see that, as we might expect, the larger (and thicker) Byrd Glacier “wins” if you will, and forces the ice from Mullock Glacier to take a sharp left turn. The contrast stretching also brings to light other structures in the ice that are related to shorter scale changes in ice flow and to very slow-moving ice at the edge of the mountains and between the two glaciers that is being pulled into their combined flow. Huge forces are at work here; sometimes the ice cracks forming crevasses while other times it is pulled like warm taffy.

Two glaciers final
Large size image (new window)
As a final view to illustrate what happens farther downstream when Byrd Glacier and Mullock Glacier come together, the image above shows the eventual merging of the ice from the two glaciers. Standing on the surface here, you'd never know whether you were standing on ice coming from Byrd Glacier or Mullock Glacier, but LIMA data can tell you the answer.

MOA Image
Large size image (new window)
Other NASA sensors also give us similar information. The Moderate Resolution Imaging Spectroradiometer (MODIS) Mosaic of Antarctica image of the same area and “backs up” the story that LIMA data has told us.

More on Flow Stripes


Dr. Robert A. Bindschadler
Want to learn more about flow stripes. Watch the video!