SCIENCE FILE / An exploration of issues and trends affecting science, medicine and the environment

Q: How do geologists measure the height of mountains?

A: They use triangulation, a mathematical technique in which they measure the angle between the ground at their feet and the top of the mountain. Knowing this angle and the distance from the point to the base of the mountain, it is relatively easy to calculate its height. In practice, they have to make a series of observations beginning at a point of known elevation, typically sea level, and working through a series of intermediate points until the final observing point is reached.

The process is easier now, however, with the advent of the Global Positioning System, which consists of satellites that orbit at known distances above the Earth. Using two or more satellites, geologists can measure their elevation at any point precisely. They then typically use triangulation to determine the heights of mountains because it is easier than climbing them. Recent measurements show that Mt. Everest is still the highest mountain on Earth at 29,028 feet, not K2 as some had thought.