A tiltmeter is a sensitive

inclinometer An inclinometer or clinometer is an measuring instrument, instrument used for measuring angles of slope, elevation, or depression (geology), depression of an object with respect to gravity's direction. It is also known as a ''tilt indicator'', ' ...

designed to measure very small changes from the vertical level, either on the ground or in structures. Tiltmeters are used extensively for monitoring

volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...

es, the response of dams to filling, the small movements of potential

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

s, the orientation and volume of hydraulic fractures, and the response of structures to various influences such as loading and foundation settlement. Tiltmeters may be purely mechanical or incorporate vibrating-wire or electrolytic sensors for electronic measurement. A sensitive instrument can detect changes of as little as one

arc second A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

. Tiltmeters have a long, diverse history, somewhat parallel to the history of the

seismometer A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The out ...

. The very first tiltmeter was a long-length stationary

pendulum A pendulum is a device made of a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate i ...

. These were used in the very first large concrete dams, and are still in use today, augmented with newer technology such as

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

reflectors. Although they had been used for other applications such as volcano monitoring, they have distinct disadvantages, such as their huge length and sensitivity to air currents. Even in dams, they are slowly being replaced by the modern electronic tiltmeter. Volcano and Earth movement monitoring then used the water-tube, long baseline tiltmeter. In 1919, the physicist, Albert A. Michelson, noted that the most favorable arrangement to obtain high sensitivity and immunity from temperature perturbations is to use the equipotential surface defined by water in a buried half-filled water pipe. This was a simple arrangement of two water pots, connected by a long water-filled tube. Any change in tilt would be registered by a difference in fill-mark of one pot compared to the other. Although extensively used throughout the world for Earth-science research, they have proven to be quite difficult to operate. For example, due to their high sensitivity to temperature differentials, these always have to be read in the middle of the night. The modern electronic tiltmeter, which is slowly replacing all other forms of tiltmeter, uses a simple bubble level principle, as used in the common carpenter level. As shown in the figure, an arrangement of electrodes senses the exact position of the bubble in the electrolytic solution, to a high degree of precision. Any small changes in the level are recorded using a standard datalogger. This arrangement is quite insensitive to temperature, and can be fully compensated, using built-in thermal electronics. A newer technology using

microelectromechanical systems MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...

(MEMS) sensors enables tilt angle measuring tasks to be performed conveniently in both single and dual axis mode. Ultra-high precision 2-axis MEMS driven digital inclinometer/ tiltmeter instruments are available for speedy angle measurement applications and surface profiling requiring very high resolution and accuracy of one arc second. The 2-axis MEMS driven inclinometers/ tiltmeters can be digitally compensated and precisely calibrated for non-linearity and operating temperature variation, resulting in higher angular accuracy and stability performance over wider angular measurement range and broader operating temperature range. Further, digital display of readings can effectively prevent parallax error as experienced when viewing traditional ‘bubble’ vials located at a distance. The most dramatic application of tiltmeters is in the area of volcanic eruption prediction.{{cite web, url=http://volcanoes.usgs.gov/About/What/Monitor/Deformation/TiltKilauea.html , title=How We Monitor Volcanoes , publisher=Volcanoes.usgs.gov , date=2008-08-13 , accessdate=2014-02-05 As shown in this figure from the USGS, the main volcano in

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

( Kilauea) has a pattern of filling the main chamber with magma, and then discharging to a side vent. The graph shows this pattern of swelling of the main chamber (recorded by the tiltmeter), draining of that chamber, and then an eruption of the adjoining vent. Each number at the peak of tilt, on the graph, is a recorded eruption.

Gallery

File:Tiltbubbs.jpg, Principle of a modern electronic tiltmeter File:UWETilt.gif, Graph showing

inflation In economics, inflation is an increase in the average price of goods and services in terms of money. This increase is measured using a price index, typically a consumer price index (CPI). When the general price level rises, each unit of curre ...

cycle of Kīlauea volcano

References

Inclinometers Seismology instruments Volcanology Geological tools

Gallery

See also

References