Volcano Watch: Tilt measurements still vital to volcano monitoring after more than a century

A water tube tiltmeter. The tiltmeter is read by looking into the portal on each pot and adjusting the sight until two pins appear to touch. In fact, one of the pins is a reflection, so having the pins almost touch establishes the exact water level within the pot. The difference in water level gives the tilt, and repeated measurements give changes in tilt over time. (Courtesy/photo)

Measuring how a volcano deforms in response to moving magma is one of the cornerstones of volcano monitoring. Our instrumentation includes a number of newer, satellite-based methods but another important instrument has been around a lot longer: the tiltmeter.