Seafloor in situ Volcanic System Monitors

1) Bottom Pressure Recorder, which measures small changes in confining pressure (at 15 second intervals) reflecting the depth below overlying sea level. This is the same instrument used for the measurement of deep-sea tides and tsunami passage and is accurate to about 1-mm sea-height equivalent. In this application, tides and transients are removed with a 40-hour low-pass filter and long-term drift are removed and remaining significant signals are interpreted to represent oceanographic effects (oscillatory) and vertical movement of the seafloor associated with magma inflation or deflation (represented by permanent baseline shifts);

2) Short-Baseline Tilt Sensors (with compass) are also included to detect ground deformation. The sensors are sensitive to about 15 microradians;

3) Volcanic Seismicity Monitor (or "rumbleometer") is a "smart sensor" tuned to record harmonic tremor associated with subsurface magma movement. As observed on land volcanos, harmonic tremor is a relatively narrow band (3-10 Hz) signal that is persistent over long periods (hours to years) and fluctuates in amplitude through time. This sensor subsystem consists of a Mark Products Model L-22 2-Hz vertical seismometer that is sampled every two minutes for sixteen seconds at 64 Hz. This time series is then processed to produce a single power spectrum from 0-16 Hz at .25 Hz increments and various other staistics;

4) Electromagnetic Current Meter is attached to each instrument to recordany significant circulation disturbances (entrainment currents) associated with hot water plume generation in response to magmatic activity;

5) Temperature Sensor is also included both to correct pressure measuremants and record disturbances in the ambient seawater.