The Earth Scientist

Volume XXVII, Issue 1
Page 15
Gumdrop Introduction to GPS
Time
2 – 3, 50-minute periods depending on student comfort level with interpreting graphs.
The teaching sequence begins with an explanation of how GPS works and how the motion of GPS
stations, permanently attached to the ground, can be measured on the scale of millimeters per years.
Students interpret GPS data time series plots to determine the motion of different GPS stations.
Lesson Objectives
n Build and use a model of a GPS monument
n
n
n
n
Understand the power of high-precision GPS to monitor movement of Earth’s surface
Learn to read and interpret GPS time series plots
Graph the direction and speed of a GPS station’s motion
Visualize deformation of the North American continental margin due to subduction of the
Juan de Fuca plate
Students first build ‘gumdrop’ GPS
receivers (Figure 2) to use in a hands-on,
follow-along exercise to learn to pinpoint
a location on the Earth’s surface using
multiple satellites. Students are then
introduced to GPS time series graphs and
use these graphs to interpret the data
from three GPS stations along a west to
east transect across Washington. Two
short video tutorials illustrating this
are available online at the Incorporated
Research Institutions for Seismology
(IRIS) website (IRIS, n.d.). Students move
their gumdrop models along the mapped data to simulate the motion of the GPS station and the
earth beneath it over time; a process that helps kinesthetic learners translate graphed data to movement.
Finally, by looking at the transect stations, students graph and model the deformation of the
western margin of the North American plate. Along this single transect, movement is largely to the
northeast due to the subducting Juan de Fuca plate. Students notice that the far western edge of
the North American plate has greater northeast movement compared to the urban corridor, while
further inland (central WA and OR) isn’t moving northeast. The next question to address is whether
the entire Pacific Northwest margin is behaving similarly.
Figure 2. Classroom set of
student-made gumdrop GPS
monuments
Locked and Loading
Time
1 ½ - 2 periods
In this activity, students analyze multiple west-to-east transects of GPS data through Washington
and Oregon to attain a regional view of how the North America plate is “locked and loading” along
its western margin in the Pacific Northwest.
© 2011 National Earth Science Teachers Association. All Rights Reserved.