The Bottom Pressure and Tilt Meter (BOPT) is a custom instrument developed by Bill Chadwick of NOAA PMEL. The BOPT is designed to measure the inflation and deflation of the seafloor at the summit of Axial Volcano using a precision pressure sensor that enables detection of the seafloor's rise and fall (i.e., "breathing") as magma (molten rock) moves in and out of the underlying magma chamber. A very precise tilt meter that measures in micro-radians will record the "tilting" of the seafloor as it deforms in response to melt migration. Similar measurements are routinely made at terrestrial volcanoes, but these will be the first to be made in real-time at an active underwater volcano. Chadwick's work has shown that the seafloor "fell" 2.4 m (7.9 feet) at the time of the eruption in April 2011.
Three of these instruments are now installed at the summit of Axial Seamount at the Central Caldera, International District 2, and Eastern Caldera sites. The BOTPTA301 instrument is located at the Central Caldera site and is connected to the MJ03F J-Box by a 50 m-long extension cable. The Central Caldera site also hosts a Broadband Seismometer and a Low Frequency Hydrophone.