Unit 3: Glaciers, GPS, and Sea Level Rise
GPS data can measure bedrock elevation change in response to the changing mass of glaciers. In this module, students will learn how to read GPS data to interpret how the mass of glaciers in Alaska and Greenland is changing, both annually and long-term. They will then apply the skills they developed and knowledge they gained to demonstrate their understanding of how their GPS data about glacial change has implications for sea level rise.
Unit 3 Learning Outcomes
- Students will observe, describe, analyze, interpret, and apply time-series GPS data related to bedrock motion near glaciers
- Students will explain how changing ice mass causes annual and decadal bedrock motion near glaciers as measured by GPS
- Students will draw on GPS data to make a societal recommendation relative to glacial change
Unit 3 Teaching Objectives
- Cognitive: Promote an understanding of the relationship between bedrock elevation and glacial size; provide examples of evidence of climate change through shrinking glaciers and their effects of society via sea level rise; provide students with a framework to understand a glacial budget and glacial flow
- Behavioral: Promote skills development in reading and interpreting bedrock GPS time-series data and understanding its relationship to changes in ice mass; provide a framework for students to approach data reading and interpretation to solve problems like a scientist; give students opportunities to convert units, identify trends, and calculate rates; develop students' ability to calculate range and understand what that means
- Affective: Encourage reflection about approaches to and difficulties with working with time-series GPS data
Context for Use
The content for Unit 3 is appropriate for introductory geology, oceanography, environmental science, and other geoscience courses; sophomore-level courses in which geodesy and/or climate studies are being introduced; or non-geoscience courses where climate studies and/or the nature and methods of science are being investigated. Unit 3 activities can easily be adapted to serve small- or large-enrollment classes. They are designed to be flexible in their context and can be executed in lecture and lab settings as an in-class activity, a homework activity, and/or a collaborative lab exercise. For example,
- Activities 1 and 2 can be completed as homework, and Activity 3 can be completed as an in-class activity or lab exercise;
- Activity 1 can be completed in class, Activity 2 completed as homework, and Activity 3 completed in lab; or
- All activities can be completed in-class and/or in lab.
In the Measuring the Earth with GPS module, this unit can be used in sequence with the other units or alone. If paired with Unit 4: Groundwater, GPS, and Water Resources, this unit should be used first, since it develops skills that students will then build on. This unit is an adaption of Ice Mass and Sea Level Change – Unit 4: An Uplifting Story of Sea Level Change. For a majors level treatment of climate change data, please see the module Understanding Our Changing Climate: Data Behind Melting Ice and Changing Sea Level.
Description and Teaching Materials
Introductory Lecture (5 minutes)
This brief lecture introduction provides context for Unit 3 by introducing students to:
- Glacial budget and flow
- Think-pair-share asking students to determine how the size of a glacier changes if the additions and subtractions are out of balance
- Brainstorm how scientists can measure the changing size of a glacier and introduce the idea that GPS can be used to measure glacial size
Slides: Unit 3 Introductory slides (PowerPoint 2007 (.pptx) 6.6MB Oct14 19)
Optional Introductory Glacier Handout for students: Unit 3 Introductory Glacier Handout (Microsoft Word 2007 (.docx) 1.9MB Jul11 19) Unit 3 Introductory Glacier Handout PDF (Acrobat (PDF) 3.6MB Jul11 19)
- This 2-page document shows pictures and poses a few questions to help students brainstorm about glaciers and how GPS might be used to measure them.
Activity 1: Observe and Describe (25–45 minutes)
In this activity, students will learn how to describe scientific data by making careful observations of it. Students will conclude by using that data to make a logical scientific interpretation. The questions guide students through the process that scientists use when they work to solve scientific questions. This particular activity uses data from a GPS station near Skagway Glacier in Alaska to better understand the impact glaciers have on the motion of nearby bedrock.
Students can complete this handout as homework, in-class individually or in small groups, or in a lab in small groups. The graphs in the handout itself should be supplemented with the large version for easier readability (see below)—if students are working in groups, one large set of graphs per group is enough. If this is done in class, suggestions for formative assessment discussions are given in the teaching tips, below.
Student activity handout:
- Student version:
- Activity 3.1 Student Exercise (Microsoft Word 2007 (.docx) 509kB Oct19 19)
- Activity 3.1 Student Exercise PDF (Acrobat (PDF) 706kB Oct19 19)
- Full size GPS graphs for easier viewing are below, beneath Activity 3
- Instructor version with rubric:
Activity 2: Animation (15–20 minutes)
In this activity, students will watch an animation that illustrates how GPS can be used to determine the amount of ice in a glacier. It describes the relationship between changing glacier mass and vertical bedrock motion.
Students can complete this handout as homework, in-class individually or in small groups, or in a lab in small groups.
Student activity handout:
- Student version:
- Activity 3.2 Student Exercise (Microsoft Word 2007 (.docx) 201kB Jul11 19)
- Activity 3.2 Student Exercise PDF (Acrobat (PDF) 316kB Jul11 19)
- Instructor version:
- YouTube: Glaciers Are Retreating—How Can We Measure the Full Ice Loss?. English and Spanish closed captions are available in YouTube; click "Settings" icon and select the subtitle version of your choice.
- File: Glaciers Are Retreating-How Can We Measure the Full Ice Loss? (MP4 Video 14.6MB Feb13 19)
Activity 3: Analyze, Interpret, and Apply (30–80 minutes)
In this activity, students will learn how to analyze and interpret scientific data after describing it. Students will conclude by using that data to support a recommendation they make about an issue relevant to society. The questions guide students through the process that scientists use when they work to solve scientific questions. This particular activity uses data from a GPS station near Helheim Glacier in Greenland to better interpret long-term trends that can be interpreted by analyzing GPS position of bedrock near the glacier.
Students can complete this handout as homework, in-class individually or in small groups, or in a lab in small groups. The graphs in the handout itself should be supplemented with the large version for easier readability (see below)—if students are working in groups, one large set of graphs per group is enough.
Student activity handout:
- Student version:
- Activity 3.3 Student Exercise (Microsoft Word 2007 (.docx) 348kB Jul11 19)
- Activity 3.3 Student Exercise PDF (Acrobat (PDF) 511kB Jul11 19)
- Instructor version with rubric:
- Includes examples of student work.
All graphs and original data files
Below are files with handouts, graphs, and data used throughout Unit 3. GPS data come from https://www.unavco.org/instrumentation/networks/status/pbo and http://geodesy.unr.edu/NGLStationPages/gpsnetmap/GPSNetMap.html
- All graphs of GPS data: Unit 3 GPS graphs (Microsoft Word 2007 (.docx) 1MB Oct19 19) Unit 3 GPS graphs PDF (Acrobat (PDF) 902kB Oct19 19)
- This handout contains larger versions of the GPS graphs. You may find it helpful to have a copy of these printed out for each table group, particularly for the graphs in which the students need to calculate an annual range of motion as well as a rate.
- All Excel files with GPS data: Unit 3 GPS data (Zip Archive 4.4MB Oct19 19)
- Contains information on the data sources as well as the original spreadsheet data and graphs from which the student exercises and handouts were generated. For instructor reference or to make changes to the way data are displayed.
Condensed version for online
This version combines Activities 1-3 into a single student exercise and was developed for the online format. It is somewhat shorter and a bit less quantitative but takes advantage of the online learning environment to add in a few websites.
- When converted to an online course manager (Blackboard, Canvas), the lab mostly self-grades with only a few questions as an exception, so it is easier to use with a lot of students where instructors can not hand-grade everything. In this format it was also designed to give students automatic feedback when they get questions wrong, so they can learn. But this is only effective is they have the opportunity to resubmit the lab answers.
- Student version: Unit 3 Online Version Student Exercise (Microsoft Word 2007 (.docx) 1MB Jul15 20) PDF (Acrobat (PDF) 1.4MB Jul15 20)
- Instructor version
- This zipped file contains the questions found in the online student exercise as exported from Blackboard. Students would need to use the student exercise file to see the figures and additional information but would answer the questions in Blackboard which can give rapid feedback on many questions. File has been successfully imported to Canvas but it showed up in Discussions.
Teaching Notes and Tips
- Students wrestle with some misconceptions related to what GPS data is measuring. For instance they may think the GPS is measuring the change in thickness of the ice instead of the ground level change. Some students think the GPS is measuring the actual sea level change. Students also confuse positions (mm) with rates (mm/yr).
- The annual vertical cycle is very evident in Greenland, but at first glance the timing might seem surprising because the bedrock uplift cycle peaks several months after the ice mass cycle reaches its minimum in late summer. Bevis et al., 2012 demonstrate that this is because the GPS vertical cycle is also responding to seasonal changes in air mass as well as ice mass. Only a very astute introductory student would notice this, but we wanted to mention the explanation in case it comes up.
Activity 1: Observe and Describe
- If Activity 1 is done as homework, you may wish to have students compare their answers for the first few minutes of class or lab to ensure they understand it. In particular, if may be useful for them to compare their answers to Questions 5, 11, and 16.
- If Activity 1 is done in class, you may wish to have the students pause after certain questions for discussion. Students can compare their answers to the answers of other groups, or you may wish to lead a full-class discussion. In particular, if may be useful for them to discuss Questions 5, 11, and 16. For Question 5, if desired, you can assign different years to different groups, and they can compare answers across years.
- Here are slides showing the GPS data and stations to aid in class discussions, if desired: Unit 3 GPS photos, locations, and graphs (PowerPoint 2007 (.pptx) 16.1MB Jul11 19)
Activity 2: Animation
- If Activity 2 is done as homework, you may wish to have students compare their answers for the first few minutes of class or lab to ensure they understand it. Or, you may wish to show the animation again and have a full-class discussion. In particular, it may be useful for them to compare their answers to Questions 8, 9, 13, and 14.
- If Activity 2 is done in class, you may wish to have the students discuss the animation after they watch it. In particular, students can compare their answers to the answers of other groups, or you may wish to lead a full-class discussion. In particular, it may be useful for them to compare their answers to Questions 8, 9, 13, and 14.
- If you do not wish to assign the handout for students to complete while watching the animation, you can instead ask Questions 8, 9, 13, and 14 as discussion questions after watching the animation.
Activity 3: Analyze, Interpret, and Apply
- We recommend that students work on Activity 3 in small groups, so they can work collaboratively to solve the problems.
- Activity 3 builds on skills learned during Activity 1 and concepts learned during Activity 2, so they should precede this activity. However, if your students are proficient at observing and describing data in graphs, it may be possible to skip Activity 1 (note that there are some concepts and skills that students build on that you may need to teach them).
- Here are slides showing the GPS data and stations to aid in class discussion, if desired: Unit 3 GPS photos, locations, and graphs (PowerPoint 2007 (.pptx) 16.1MB Jul11 19)
- The Activity 3 Answer Key also includes a rubric for the more complex question related to providing sea level hazard advice and examples of student answers. If your students struggle with how to write high-quality answers, you could consider sharing the rubric and example student answers and asking students to evaluate what makes a high-quality answer. This may help them improve for next time.
Details on scientific concepts of interest to instructors
- This unit deals with sea level rise in a somewhat simplistic manner because of the introductory nature of the intended courses. Although ice and glacier melting taken together is the single biggest cause of sea level rise globally, sea level rise is actually a result of a variety of sometimes competing processes. The majors-level module Understanding Our Changing Climate: Data Behind Melting Ice and Changing Sea Level contains a more nuanced treatment of sea level rise. For instance thermal expansion is an important part of current sea level rise and is dealt with the majors-level module [link /getsi/teaching_materials/climate_change/unit2.html Unit 2: Global Sea Level Response to Temperature Changes: Temperature and Altimetry Data']. Other contributions to local differences include: uplift, subsidence, or changes in local gravity field.
- The annual vertical cycle is very evident in Greenland, but at first glance the timing might seem surprising because the bedrock uplift cycle peaks several months after the ice mass cycle reaches its minimum in late summer. Bevis et al. 2012 demonstrate that this is because the GPS vertical cycle is responding to seasonal changes in air mass as well as ice mass. Only more astute students will notice this, but we wanted to mention the explanation in case it comes up. The GRACE data show the cycling timing that is not complicated by air mass changes.
- Many times geoscientists jump to concluding that vertical changes are a results of isostasy. It needs to be clarified that what is being studied in this unit is an elastic response of the rocks themselves, not an isostatic adjustment that involves viscoelastic processes. Elastic response is instantaneous and ~20 times smaller; whereas isostatic viscoelastic adjustment associated with post-glacial rebound has time scales of hundreds to thousands of years, but ultimately the adjustment will be much greater. Most likely there is some component of the long-term trend in the GPS measurements that is related to isostatic adjustment, but it is not what causes the seasonal and year-to-year variations. Depending on the length of the time series and the distance between the ice front and GPS station, there may also be a flexural response that will depend on the effective elastic thickness that is a function of the crust and mantle rheological properties. More about the differences between elastic, isostatic, and flexural responses are covered in the majors-level climate change module Understanding Our Changing Climate: Data Behind Melting Ice and Changing Sea Level.
Activities 1 and 2 can be assessed formatively by using some of the questions as prompts for discussions, as described above in Teaching Notes and Tips. In addition, if the students are working in class or lab on the questions, the instructor can circulate and listen to student conversations and answer questions to ensure that the desired learning is occurring.
Activity 3 (as well as Activities 1 and 2, if desired) can be used as the summative assessment for this unit (Unit 3: Glaciers, GPS, and Sea Level Rise). In addition to the student activity handout, the following assessments can be used as homework, quiz, or exam questions. There are open-ended and multiple-choice questions included. Note that the Assessment page also includes more general summative assessments that can be used for this unit as well.
- Student assessment questions:
- Unit 3 Additional Assessment Questions (Microsoft Word 2007 (.docx) 732kB Jul11 19)
- Unit 3 Additional Assessment Questions PDF (Acrobat (PDF) 862kB Jul11 19)
- associated full size graphs (Acrobat (PDF) 506kB Oct14 19)
- Instructor assessment questions with grading rubrics:
References and Resources
This unit is an adaption of Unit 4: An Uplifting Story of Sea Level Change.
Additional Resources for Instructors:
- If your students have difficulties converting units, a helpful webpage is The Math You Need When You Need It: How Do I Change Units
- There is a UNAVCO GPS Spotlight on Station KULU that includes information, photos, and data that can be used to supplement Part 3.
- There is a UNAVCO GPS Spotlight on GLS1, a station on a glacier that includes information, photos, and data that can be used to supplement Part 3.
- There is a UNAVCO GEODETIC Science Snapshot on Observing Abrupt Melting in the Greenland Ice Sheet and Relating Air Mass Changes to Bedrock Changes.
- If you want your students to learn more about evidence for the loss of glaciers in Greenland, an interesting activity that uses additional geodectic data is Ice and Sea Level Changes, Unit 3: Warm with a Chance of Melting.
- Bevis et al., 2012 Bedrock displacements in Greenland manifest ice mass variations, climate cycles and climate change