top banner image of tubeworms
NeMO home NeMO Net home NOAA home
  NeMO Net Bottom Pressure Recorder (BPR)
     
 

The NeMO Net Bottom Pressure Recorder (BPR) is located near the center of Axial caldera at the summit of the volcano. BPRs precisely measure the pressure from the overlying ocean, and by doing so they can detect vertical movements of the seafloor due to volcanic activity (for example, if the seafloor were uplifted the BPR would measure a pressure decrease). The NeMO Net BPR sends back four pressure measurements per hour from the seafloor (purple,in the plots below). After the predictable variations from ocean tides (black curve) are removed, the de-tided BPR data (red) is then evaluated to look for any sudden vertical movements of the seafloor that may signal the onset of a volcanic eruption.

 
 
 
     
  What's new this year?
This is the first year we have had a BPR linked into NeMO Net. Also, we are experimenting this year with a longer-range "omni-directional" acoustic modem on the BPR. This allows the instrument to be farther away from the NeMO Net surface buoy. In future years we hope this will allow multiple instruments to be positioned over a larger area, while still using a single surface buoy as a communication hub. The two RAS samplers have shorter-range "directional" acoustic modem transducers like we have used in previous years. This is why the NeMO Net buoy is located close to the RAS instruments and farther away from the BPR.

Previous results from BPR's at Axial
There were BPRs in each of two "rumbleometer" instruments that were in place at Axial volcano when the 1998 eruption occured. The 1998 eruption caused a large volume of magma that had been stored in a reservoir beneath Axial's summit caldera to be removed and intruded into the south rift zone. The removal of this large volume of magma caused the whole summit of Axial seamount to subside, just like a balloon that had some of the air taken out of it. The BPR that was at the center of Axial caldera at the time of the 1998 eruption measured 3.2 meters (10.5 feet!) of subsidence. Another BPR was in the rumbleometer that was stuck in the 1998 lava flow until it was extracted in the summer of 1999. This second BPR showed a subsidence of 1.4 meters (4.6 feet) at the eruption site, which is 3.5 km (~2 miles) from the caldera center. These measurements can be used to model the depth of the magma reservoir beneath Axial caldera. For more information see the NeMO Explorer Rumbleometer virtual site.

 
 
. BPR images
 
  BPR on deck, click for full size   The BPR (Bottom Pressure Recorder) that was deployed in the center of Axial caldera. The white box in the foreground covers the pressure sensor. The white horizontal cylinders contain batteries. The silver vertical cylinder houses the CPU (computer controller). The vertical yellow cylinder is the acoustic release for the anchor. The smaller yellow cylinder in the silver frame in the background contains the acoustic modem transducer.  
         
  plot of BPR data from 1998 eruption at Axial   Click to see a plot of BPR data recorded during the 1998 eruption at Axial volcano.  
         
spacer image
horizontal bar
spacer image
NeMO 2002 |About NeMO | Expedition | NeMO Net 2002 | Explorer | Dive! | Education
spacer
horizontal bar
spacer
spacer imagePrivacy Notice | Disclaimer | nemo.webmaster@noaa.gov