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 Seamount 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, is measuring "tilting" of the seafloor as it deforms in response to melt migration and/or faulting events. Similar measurements are routinely made at terrestrial volcanoes, but these are 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. BOTPTA303 within the International District 2 site is connected to the MJ03D J-Box by a 50 m-long extension cable. Other instruments at International District 2 include a 3-D Single Point Velocity Meter, and a short period seismometer.