The OHA-GEODAMS Seafloor Observatory
@geodams.bsky.social
OHA-GEODAMS is a submarine geodetic, hydro-acoustic and seismological observatory aimed at measuring seafloor spreading as it happens across the Southeast Indian Ridge and Amsterdam transform fault (37ºS). Funded by https://anr.fr/Project-ANR-24-CE49-7271
If it all goes well, our now-complete observatory will be the first to document seafloor spreading and transform faulting events with geodesy, hydro-acoustics, and seismology! 🤞
February 1, 2025 at 7:18 AM
If it all goes well, our now-complete observatory will be the first to document seafloor spreading and transform faulting events with geodesy, hydro-acoustics, and seismology! 🤞
But pressure at the seafloor can fluctuate for many reasons! Tides, ocean dynamics, etc... To avoid misinterpreting an oceanographic signal as a tectonic signal, we deployed a mooring that will help us assess how the weight of the water column changes through time.
February 1, 2025 at 7:18 AM
But pressure at the seafloor can fluctuate for many reasons! Tides, ocean dynamics, etc... To avoid misinterpreting an oceanographic signal as a tectonic signal, we deployed a mooring that will help us assess how the weight of the water column changes through time.
The A-0-A lets us measure vertical displacements of the seafloor: if the ground swells, the instrument will go up, feel less water weight, and the pressure will decrease.
February 1, 2025 at 7:18 AM
The A-0-A lets us measure vertical displacements of the seafloor: if the ground swells, the instrument will go up, feel less water weight, and the pressure will decrease.
Last, but not least, we also recovered and re-deployed an A-0-A pressure sensor, right in the middle of the ridge's axial valley. This state-of-the-art instrument corrects its own drift by regularly re-calibrating itself against an inner chamber where the pressure is known.
February 1, 2025 at 7:18 AM
Last, but not least, we also recovered and re-deployed an A-0-A pressure sensor, right in the middle of the ridge's axial valley. This state-of-the-art instrument corrects its own drift by regularly re-calibrating itself against an inner chamber where the pressure is known.
But last week we succeeded in recovering and re-deploying 1 beacon from the ridge network, and 1 from the transform network. The first year of data did not disappoint! #ToBeContinued
January 31, 2025 at 4:18 AM
But last week we succeeded in recovering and re-deploying 1 beacon from the ridge network, and 1 from the transform network. The first year of data did not disappoint! #ToBeContinued
Some deployments can take up to 11 hours, as we go through trial-and-error on different target sites with the tripod hanging from the ship on a 2-km long cable.
January 31, 2025 at 4:18 AM
Some deployments can take up to 11 hours, as we go through trial-and-error on different target sites with the tripod hanging from the ship on a 2-km long cable.
When we redeploy a transponder+tripod, we must always make sure it's standing upright on the seafloor, and that it can still ping its colleagues.
January 31, 2025 at 4:18 AM
When we redeploy a transponder+tripod, we must always make sure it's standing upright on the seafloor, and that it can still ping its colleagues.
Once the beacon is on board, we download the data, and place it atop a new tripod, to be re-deployed from the back deck, by cable. @jbeesau.bsky.social @pyraumer.bsky.social @annebriais.bsky.social @sismolise.bsky.social
January 31, 2025 at 4:18 AM
Once the beacon is on board, we download the data, and place it atop a new tripod, to be re-deployed from the back deck, by cable. @jbeesau.bsky.social @pyraumer.bsky.social @annebriais.bsky.social @sismolise.bsky.social
Spotting the beacon when it surfaces can be challenging! It's essentially a meter-long pink cylinder encased in a yellow buoy. Lucky for us, the bridge crew has sharp eyes!
January 31, 2025 at 4:18 AM
Spotting the beacon when it surfaces can be challenging! It's essentially a meter-long pink cylinder encased in a yellow buoy. Lucky for us, the bridge crew has sharp eyes!
By measuring acoustic travel times and the speed of sound in the ocean, we can infer how the mid-ocean ridge axis stretches, and the adjacent transform slips.
January 31, 2025 at 4:18 AM
By measuring acoustic travel times and the speed of sound in the ocean, we can infer how the mid-ocean ridge axis stretches, and the adjacent transform slips.
As tectonic plates drift further and further apart on either side of the mid-ocean ridge, sound waves take a longer and longer time to travel from beacon to beacon.
January 31, 2025 at 4:18 AM
As tectonic plates drift further and further apart on either side of the mid-ocean ridge, sound waves take a longer and longer time to travel from beacon to beacon.
The core of the OHA-GEODAMS project is to measure active deformation for 3 years on the Southeast Indian Ridge and the Amsterdam transform fault. To this end, in February 2024, we deployed 15 acoustic beacons that have been pinging each other every few hours ever since.
January 31, 2025 at 4:18 AM
The core of the OHA-GEODAMS project is to measure active deformation for 3 years on the Southeast Indian Ridge and the Amsterdam transform fault. To this end, in February 2024, we deployed 15 acoustic beacons that have been pinging each other every few hours ever since.
We then release the weight, sinking the entire mooring down to the seafloor in a matter of minutes.
January 30, 2025 at 6:17 PM
We then release the weight, sinking the entire mooring down to the seafloor in a matter of minutes.
We start by deploying the float containing the hydrophone from the back deck, then unroll the ~2 km long mooring...
January 30, 2025 at 6:17 PM
We start by deploying the float containing the hydrophone from the back deck, then unroll the ~2 km long mooring...
Using broadband OBSs, we will also carry out compliance measurements: that's looking at how the oceanic crust responds to changes in water pressure at the seafloor, due to tides and ocean dynamics. This should tell us whether magma is present at depth in the crust.
January 30, 2025 at 9:17 AM
Using broadband OBSs, we will also carry out compliance measurements: that's looking at how the oceanic crust responds to changes in water pressure at the seafloor, due to tides and ocean dynamics. This should tell us whether magma is present at depth in the crust.
This local network will let us locate the events with high precision to characterize how mid-ocean ridge faults slip.
January 30, 2025 at 9:17 AM
This local network will let us locate the events with high precision to characterize how mid-ocean ridge faults slip.
We deployed 7 Ocean Bottom Seismometers (OBSs) to record earthquakes and other signals emitted by the Southeast Indian Ridge and the Amsterdam transform fault.
January 30, 2025 at 9:17 AM
We deployed 7 Ocean Bottom Seismometers (OBSs) to record earthquakes and other signals emitted by the Southeast Indian Ridge and the Amsterdam transform fault.
For the last ~10 days, we've been hard at work on and around the Southeast Indian Ridge at 37ºS to recover and redeploy a bunch of geophysical instruments. Let's break it down 👇
January 30, 2025 at 9:17 AM
For the last ~10 days, we've been hard at work on and around the Southeast Indian Ridge at 37ºS to recover and redeploy a bunch of geophysical instruments. Let's break it down 👇
This glider is equipped with a hydrophone (48kHz) to record the underwater soundscape, and in particular the cetaceans (i.e., blue whales, fin whales, killer whales, sperm whales, etc.). The glider will navigate south and west of Amsterdam, diving down to 1000 m, driven by buoyancy changes.
January 20, 2025 at 6:16 AM
This glider is equipped with a hydrophone (48kHz) to record the underwater soundscape, and in particular the cetaceans (i.e., blue whales, fin whales, killer whales, sperm whales, etc.). The glider will navigate south and west of Amsterdam, diving down to 1000 m, driven by buoyancy changes.
In order to prevent the glider from colliding with the Marion Dufresne, it had to be launched at a certain distance. To do so, 3 brave members of our GEODAMS team, Anne, Séverine and Diane, boarded a workboat with 2 LDA crew members.
January 20, 2025 at 6:16 AM
In order to prevent the glider from colliding with the Marion Dufresne, it had to be launched at a certain distance. To do so, 3 brave members of our GEODAMS team, Anne, Séverine and Diane, boarded a workboat with 2 LDA crew members.
A few days ago, we deployed a Sea Explorer glider developed by ALSEAMAR and owned by ENSTA Bretagne at the location of our first hydrophone, southeast of Amsterdam island.
January 20, 2025 at 6:16 AM
A few days ago, we deployed a Sea Explorer glider developed by ALSEAMAR and owned by ENSTA Bretagne at the location of our first hydrophone, southeast of Amsterdam island.
Measuring travel time and knowing the speed of sound in water, the echosounder provides depth measurements along swaths, which we combine to create bathymetric maps, revealing underwater landscapes, submarine volcanoes, and ridges.
January 19, 2025 at 12:02 PM
Measuring travel time and knowing the speed of sound in water, the echosounder provides depth measurements along swaths, which we combine to create bathymetric maps, revealing underwater landscapes, submarine volcanoes, and ridges.
As we make our way to our study area, we map the seafloor under the ship! 🌊 Our multibeam echosounder sends acoustic waves to the ocean floor and records how much time they take to bounce back.
January 19, 2025 at 12:02 PM
As we make our way to our study area, we map the seafloor under the ship! 🌊 Our multibeam echosounder sends acoustic waves to the ocean floor and records how much time they take to bounce back.
Planning our upcoming deployments like they schedule sketches on Saturday Night Live
(with multiple new versions since that v1 😜) #GEODAMS
(with multiple new versions since that v1 😜) #GEODAMS
January 19, 2025 at 11:47 AM
Planning our upcoming deployments like they schedule sketches on Saturday Night Live
(with multiple new versions since that v1 😜) #GEODAMS
(with multiple new versions since that v1 😜) #GEODAMS