The most dramatic application of tiltmeters is in the area of volcanic eruption prediction. As shown in this figure from the USGS, the main volcano in Hawaii (Kilauea) had a habit of filling the main chamber with magma, and then discharging to a side vent. The graph shows this repeated action, with a 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.