Grounding Line Location using Echograms - CReSIS

ANSWER KEY
Q1) Figure 4 is illustrates just some of the possible features students may label. Depending on their diagram, they may
have other features labeled such as moulins, crevasses, margins, ablation zone, accumulation zone, etc. Another more
complete diagram of a glacier can be obtained from Indiana University
(http://www.indiana.edu/~sierra/papers/2008/gray_clip_image002.jpg).
Figure 4 - Basic glacier features (from CReSIS 'Glaciers in Motion' project)
Q2) Answers will vary. The center part of the glacier should flow the fastest as there is less friction with the margins or
sides of the glaciers (mountains). A glacier may speed up if the surface slope changes or if water reaches the bed and
helps to reduce friction between the bottom of the glacier and the bedrock.
Q3) Researchers can use a variety of technologies from GPS units placed on the actual glacier to monitor motion to the
radar technologies mentioned in the background of this lesson. For radar, electromagnetic signals are sent from an
airborne platform and the reflections from various surfaces (snow surface, bedrock, water, etc.) are detected.
Q4) This echogram illustrates the snow surface, bedrock, ice, water, and the grounding line. You can also see the
coordinates along the flight path indicating the direction of flight.
Q5) The snow surface is the initial reflection. The bedrock is the dark reflection towards the middle to bottom of the
echogram, visible underneath the snow surface line. This is typically more jagged than the snow surface. The grounding
line can be determined as the location where the bedrock echo is distorted and blurry by the reflection of the radar
signal by water.
Q6) ~80.5° N, 60.4° W. The coordinates should fall between 80.407° N and 80.605° N, and 59.754° W and 60.759° W.
Q7) The plane is flying to the northwest, from the interior of Greenland, along Petermann Glacier.