By Rachel Teasdale
Bright but overcast skies with calm wind and seas.
What’s happening today?
The Jason pressure dive continues for the second day. This morning the SCPR (Self Calibrating Pressure Recorder) was recovered, after two years on the seafloor. This afternoon AUV Sentry will be recovered after nearly 24 hours of mapping in the caldera.
|Bathymetric map of the Axial Seamount caldera (horseshoe shape open to the south) with north and south rift zones and lavas of the April 2015 eruption outlined with black lines.|
As previously discussed, the goal of the pressure dive is to use the array of the Bottom Pressure Recorders (BPRs) to precisely measure the depth of the seafloor at Axial Seamount over time. As magma moves up from deeper sources, the seafloor rises, in a process referred to as inflation. When magma erupts (or moves laterally in the volcano), the seafloor lowers, known as deflation. Following a series of pressure dives in 2011 and 2013, Bill Chadwick, Scott Nooner and their colleagues used their high precision pressure data to determine that since the 2011 eruption, Axial Seamount had inflated approximately 60 cm/yr (1.9 ft/yr).
As pressure surveys have continued to monitor the movement of magma at Axial Seamount, colleagues at the Monterey Bay Aquarium Research Institution (MBARI) have used sonar instruments to map the surface of the seafloor. Multibeam sonar mapping like that described for AUV Sentry (< link to Sentry blog 16 August), works by emitting sound waves that are reflected from the ocean floor and returned to receivers. The time between the emitted and received reflected pulses is used to determine the distance the sonar traveled to the seafloor and back. Maps of the seafloor are color coded, usually with warm colors representing shallow (or high seafloor topography) and deeper (lower) seafloor topography represented by cool colors (see map above).
|Image of MBARI’s AUV D. Allan B in 2006.|
Based on the continuous inflation rates observed from 2011-2013 by the pressure sensors and the continued inflation measured by the MBARI AUV into 2014, Chadwick and Nooner were able to successfully forecast that the next eruption at Axial Seamount would occur sometime in 2015. The April 2015 eruption proved their forecast correct. We will explore more about eruption forecasting at Axial Seamount in an upcoming blog.