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
The OHA-GEODAMS Seafloor Observatory
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What a day!
We visited Kerguelen station, met king penguins and elephant seals, and walked on the "Desolation Island".
Just a few days before reaching the OHA-GEODAMS area, this was an unforgettable stop in the middle of the Southern Ocean.
Cheers to the penguins 🐧
On our way to the Southeast Indian Ridge and it’s all hands on deck 🚢🔧
From building tripods for acoustic beacons to installing the transducer and modem in the ship’s forward hold, operational prep is well underway!
The OHA-GEODAMS team is back to document how the Indian Ocean grows.
Cruise #3 on board Marion Dufresne left La Réunion Island a few days ago to maintain the multi-sensor observatory on the South East Indian Ridge. Follow us on this new adventure!
(credit photo: Ewen & Didier)
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.
The OHA-GEODAMS Seafloor Observatory
The OHA-GEODAMS Seafloor Observatory
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.
The OHA-GEODAMS Seafloor Observatory
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 2026 GEODAMS team safely arrived close to Possession Island in the Crozet archipelago a few days ago. A penguin crowd welcomed us under a very bright sky and with the traditional croziflette that follows... 🐧 🍽️
We’ve had our fill, both for the eyes and the stomach.
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! 🤞
