Glaciers Lab

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Chemeketa Community College *

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Apr 3, 2024

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Questions or comments please contact education AT unavco.org. Version July 7, 2020 Page 1 Measuring Earth with GPS, Unit 3: Glaciers Karen M. Kortz (Community College of Rhode Island) and Jessica J. Smay (San Jose City College) This is the full lab handout. It includes the information you need to complete the lab. However, you will submit your lab answers on Blackboard. 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 GPS stations precisely record the position of the solid ground they are on, and they were first installed to measure plate motion. However, geoscientists analyzing GPS data realized that earthquakes and plate motion are not the only geological processes that cause the ground to move. In this first part of the lab, you will look at scientific data from a GPS station on the bedrock near Skagway Glacier in Alaska by making careful observations, and you will use those observations to make a scientific interpretation. Part 1: Why is the ground moving up and down? Examine Figure 1 that shows the GPS data. The first thing to do when looking at a graph is to read the title, look at the axes, and make some general observations. 0 50 100 150 200 250 300 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Vertical (mm) Year V ERTICAL P OSITION -SKAGWAY, AK (STATION-AB44) Daily position 30-day average Figure 1. Vertical GPS data from station AB44 on the ground near Skagway Glacier in Alaska from the beginning of January 2006 to the end of December 2017.

Measuring Earth with GPS, Unit 3: Glaciers Questions or comments please contact education AT unavco.org. Version July 7, 2020. Page 2 1. What does the vertical (y-) axis show and what are the units? time in years vertical position in millimeters motion in millimeters per year 2. Look at the time scale. The points on the graph rise and fall in a cycle that lasts how long? day month year decade When scientists first noticed that the ground was moving up and down each year, they wanted to know why. Two of the hypotheses are: Hypothesis A : The ground elevation rises because the ground expands when it freezes, and it lowers when the ground contracts as it thaws. Hypothesis B : The ground elevation lowers because the weight of the snow presses it down, and the ground elevation rises when the snow melts. Geoscientists often work with more than one hypothesis (called “multiple working hypotheses”). You will try to determine which one explains the data better. First, let’s make some predictions based on these hypotheses, and then we will later compare the GPS data to them. 3. If Hypothesis A is correct, then the highest point each year would be during the months of _______________. If Hypothesis B is correct, then the highest point each year would be during the months of _______________. 4. Look at several different years on the graph. During what months is the ground the highest? 5. Approximately how far is the ground moving up and down each year? This distance is called the annual range. About 2 millimeters, which is about the thickness of a penny About 40 millimeters, which is about the length of a paper clip About 700 millimeters, which is about the height of a table 6. Which parenthesis shows the annual range? 7. What number is the best to use when describing the movement of the ground over a single year to help compare it to other years? Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Elevation low high A B

Measuring Earth with GPS, Unit 3: Glaciers Questions or comments please contact education AT unavco.org. Version July 7, 2020. Page 3 The range of vertical movement, because it is consistent from year to year, even though the highs and lows aren’t the same from year to year. The height of the high point, because it shows how high the ground rises each year, even though it is changing from year to year. The GPS data show when and how much the ground is moving, but they doesn’t show why. We need to look at other data to help us learn why, and below are photos of the GPS station to help do that. The GPS stations are drilled deep into the bedrock, so the only thing that causes the station to move is the movement of the bedrock. 8. Find the months that the Figure 2 and 3 photos were taken. Which choice correctly labels the arrows? Figure 2: A snow; Figure 3: B snow Figure 2: A no snow; Figure 3: B snow Figure 2: B snow; Figure 3: A no snow Figure 2: B no snow; Figure 3: A snow Figure 2. Photo of the GPS station AB44 taken October 19, 2016. Photo from: https://www.unavco.org/instrumentation/n etworks/status/pbo/photos/AB44 Figure 3. Photo of the GPS station AB44 taken December 20, 2011. Photo from: https://www.unavco.org/instrumentation/n etworks/status/pbo/photos/AB44 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Elevation low high A B

Measuring Earth with GPS, Unit 3: Glaciers Questions or comments please contact education AT unavco.org. Version July 7, 2020. Page 4 9. (2 points) Look at your predictions based on the hypotheses, and look at your observations of the data. Which hypothesis is best supported by the data and what causes the height of the ground to change over the course of a year? Hypothesis A, the weight of the snow Hypothesis A, the freezing of the ground Hypothesis B, the weight of the snow Hypothesis B, the freezing of the ground Part 2: Animation Watch the animation titled, Glaciers are Retreating: How can we measure the full ice loss? (https://www.youtube.com/watch?v=qmSrAQpolj4). Keep in mind that the GPS stations are installed on the bedrock next to the glacier, not the glacier itself. Pay particular attention to what is causing the yearly change in GPS height compared to the long-term trend in change. 10. What explains the direction and reason that ice sheets flow in Greenland? They flow uphill towards the mountains because of fjords. They flow uphill towards the mountains because of the grounding line. They flow downhill towards the ocean because of crevasses. They flow downhill towards the ocean because of gravity. 11. What happens to the bedrock’s vertical surface when glacial mass is added to the ground and when it is removed? When glacial mass is added, it goes up. When glacial mass is removed, it goes up. When glacial mass is added, it goes up. When glacial mass is removed, it goes down. When glacial mass is added, it goes down. When glacial mass is removed, it goes up. When glacial mass is added, it goes down. When glacial mass is removed, it goes down. 12. What causes the yearly up and down motion of the bedrock near glaciers? Seasonal changes with the ground freezing in the winter (causing the ground to rise) and the ground thawing in the summer (causing the ground to lower) Seasonal changes with snow melting in the summer (causing the ground to rise) and snow accumulating in the winter (causing the ground to lower). The glacier is melting and getting smaller, so it weighs down less on the ground, causing the ground to rise. The climate is getting warming, so the ground is expanding due to the extra heat, causing the ground to rise.

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