A tiltmeter is a device used to measure minute changes in the inclination of the Earth's surface in order to detect seismic or volcanic activity. Geologists also use tiltmeters to determine if glaciers expand or collapse due to freezing or melting.
Electronic tiltmeters are widely used as portable sensing instruments to reveal changes due to mining, tunneling and excavating. These devices monitor dams, retaining walls and structures to measure possible damage. Government and civilian organizations use tiltmeters to sense changes in the slope of the ground.
Electronic tiltmeters work by measuring changes in slope within a small vessel containing a bubble alongside conducting fluid. Electrodes in the liquid measure the bubble's position based upon how much electricity is generated. When there is less fluid on the electrode, less voltage is detected. When more fluid touches the electrode, more electricity runs through the wire. These small changes in electricity can measure slope differences down to one-tenth of a microradian.
Electronic tiltmeters have been used since the 1960s in Hawaii to measure volcanic activity. The apparatus has been utilized by volcanologists in some form since 1912. There are 13 such devices on Mauna Loa and Mount Kilauea in Hawaii to provide continuous data.