Yellowstone Gravity

Gravity influences every person and object in the universe. This map was designed by the National Geodetic Survey (NGS) to educate the public on how gravity varies subtly from one region to another and how this fact is applied in geodesy. Almost every geodetic measurement depends in a fundamental way on the Earth’s gravitational field. Yellowstone National Park was chosen to observe the free-air gravity anomaly because its gravity distribution is highly influenced by the dense magma near the Earth’s surface—called a caldera.

When analyzing the gravity variations over a local area, there is a need to eliminate global gravitational forces from the observed values. The free-air gravity anomaly eliminates the global gravitational forces due to the Earth’s deepest masses and the centrifugal forces caused by its rotation. It has a high positive correlation to crustal elevation changes, providing local gravity variations based on topography and density variations. These local gravity variations assist geodesists in creating accurate geoid models.

Courtesy of NOAA–National Geodetic Survey.