How do scientists know Alaska is so active?
Scientists use GPS measurements to measure plate motions and deformation in Alaska. The Plate Boundary Observatory constantly collects data about where their GPS stations are at any given time and compares each location to the instruments around it.

The map below shows the location of PBO sites in North America.
How does GPS work?
What does the data mean?
Question:
How many satellites are needed to obtain a GPS location?