See the Unseen

Searching for submerged archaeological sites

By Adramar

Choice of site for re-immersion, the rock of Bizeux Saint-Malo (2016-01-01) by Nicolas Job & ADRAMARAdramar

An ocean of the unknown

It's difficult to imagine just what's waiting to be found at the bottom of our oceans. Only 10% of the ocean floor has been explored. For underwater archaeologists, that means there are potentially thousands of archaeological sites just waiting to be discovered!

Discovery of a cannon partly silted up (2003-07-25) by Teddy Seguin & ADRAMARAdramar

As luck would have it…

Most submerged archaeological sites were discovered accidentally, by sheer luck. From amateur divers and fishing crews to offshore oil explorers, anyone out at sea is a potential shipwreck discoverer.

Hermine-Bretagne, Adramar archaeological research vessel (2009-01-01) by Teddy SeguinAdramar

Using geophysical instruments for underwater archaeology

Archaeologists use geophysical instruments to track down shipwrecks on the sea floor. The Hermine-Bretagne research vessel tows a side-scan sonar called Fish.

Installation of geophysical instruments on board a semi-rigid (2009-01-01) by Teddy SeguinAdramar

Installing geophysical instruments on board

Setting up geophysical devices is not always easy at sea, particularly on board a semi-rigid boat.

Preparation of sonar on the Hermine Bretagne bridge (2009-09-03) by Teddy Seguin & ADRAMARAdramar

Preparing the sonar on the Hermine-Bretagne's deck

The use of geophysical devices like sonars requires a comprehensive technical and maritime skillset.

Explanatory diagram of the operation of the side scan sonar (2009-01-01) by Teddy SeguinAdramar

Diagram explaining how the side-scan sonar works


The side-scan sonar emits soundwaves, which allow the user to obtain an image of the seabed and any underwater structures or wreckages—without needing to dive!

Launching of side scan sonar and magnetometer from Hermine-Bretagne (2009-01-01) by Teddy SeguinAdramar

Launching the sonar and magnetometer

Geophysical instruments that allow the detection of anomalies on the seabed are towed from the rear of the boat.

Sonar operator performing geophysical data acquisition (2009-01-01) by Teddy SeguinAdramar

Sonar operator collecting data

An operator continually checks and analyzes the data gathered by the sonar.

Side-scan sonar image of the Laplace wreck (2009) by ADRAMARAdramar

Side-scan sonar image of the Laplace wreck

Without having to send a diver into the water, the sonar can obtain a lot of information about the layout of the site on the seabed. Here, the wreck of the Laplace weather ship, which sank in 1950, is tipped over and split in two.

Sonar view of the Fetlar wreck (2011-06-24) by ADRAMARAdramar

The details of a wreck revealed by sonar image

The sonar image provides a precise and fast record of a wreck, as can be seen by the image of the Fetlar cargo ship, which sank in 1919 off the coast of Saint-Malo, France. Measuring 56 meters in length, this wreck has been frozen in time for a century, upright on its keel on the seabed.

The details of a wreck revealed by sonar image

We can make out the entrances to the holds for loading goods.

The details of a wreck revealed by sonar image

The remains of the cargo ship's steam boiler at the center of the wreck.

The details of a wreck revealed by sonar image

To the rear of the ship, the shadow generated by the sonar even allows us to see that the ship's propeller escaped looting and remains in place!

Artiglio and Florence H side scan sonar images (2009) by ADRAMARAdramar

The tragedy of the Artiglio

In 1930, the Artiglio, a vessel specializing in the excavation of shipwrecks, attended the wreck of the Florence H, which sank in 1918 carrying tons of gunpowder. Tragedy struck when the wreck exploded with such force that the Artiglio sank immediately.

The tragedy of the Artiglio

About a hundred meters away from the Artiglio, the remains of the Florence H wreck are spread out over a distance of 70 meters in complete smithereens. Eighty years later, the scene appears to be frozen, preserved under 20 meters of water.

Commemorative plaque of the sinking placed on the wreck of the Artiglio (2008-10-09) by Teddy Seguin & ADRAMARAdramar

A dive down to the Artiglio

A commemorative plaque has been placed on the wreck of the Artiglio in memory of the catastrophe that claimed 12 lives. Witnesses to the event claim to have seen the Artiglio sent flying upwards to a considerable height before falling back down and sinking in less than 45 seconds.

Archive relating the sinking of the ship Le Chariot (1676-04-11) by ADRAMARAdramar

In search of old shipwrecks: the good ship Le Chariot

Very old shipwrecks no longer have the shape of a ship and are totally or partially buried.
This archive document mentions the loss of a ship called Le Chariot in 1676 off the coast of the island ofHoëdic, France. The vessel was loaded with munitions.

Map of Belle-Isle and the isles of Houat and Hédic, by Bellin (1764-01-01) by ADRAMARAdramar

Hunting for clues to narrow down the search area

Less than 100 years after the royal ship Le Chariot sank off the coast of Hoedic island due to hitting a previously uncharted rock, the map drawn by Bellin in 1764 names a rock as "The descent of Le Chariot", thereby indicating the location of where it sank.

The search area takes shape!

Thanks to this old map, the search area was greatly reduced; however, the sea is vast, and looking for a wreck by means of diving would be a very long and haphazard affair.

Side scan sonar image of the Chariot archaeological site (2009-01-01) by ADRAMARAdramar

Locating the archaeological site

Geophysical exploration using sonar may not allow you to clearly identify an archaeological site, but it does let you see anomalies that could indicate the possible presence of a site. In the center of the image, we can see some anomalies that stand out against the seabed.

Diving check of geophysical anomalies on the wreck of the Chariot (2009-01-01) by Teddy Seguin & ADRAMARAdramar

Diving to verify geophysical anomalies

The archaeologist has to dive to verify any anomalies, which could be rocks, old lobster pots, or pollution. In this case, the checks revealed a cargo of cannons. This is surely the site of the Le Chariot wreck, since the word "munitions" also referred to cannons in the 17th century!

Immersion of the magnetometer aft of the ship (2009-01-01) by Teddy SeguinAdramar

The magnetometer: Perfect for buried wrecks

If a shipwreck is totally buried, it will not appear on a sonar image. Archaeologists also use another machine called a magnetometer, which detects the presence of metal not just underwater but even underneath the sand.

Sonar profile and magnetic anomalies on the archaeological site of the cannon off Quiberon (2009-01-01) by ADRAMARAdramar

Magnetic anomalies on a pile of cannons

The magnetometer will reveal the presence of cannons or anchors hidden in the sand.

Control of magnetic anomalies in diving prospecting using a metal detector (2018-01-01) by Jacques Le LayAdramar

Diving to check magnetic anomalies

Archaeologists can also check magnetic anomalies during explorations by diving and using a metal detector.

Geophysical prospecting and expertise dives off Locmariaquer, Adramar (2013-01-01) by Nicolas Job & ADRAMARAdramar

Geophysical exploration and verification dives off the coast of Locmariaquer

Credits: Story

L'ADRAMAR remercie l'ensemble des soutiens et partenaires de ces projets et particulièrement la région Bretagne, le conseil départemental d'Ille et Vilaine, la ville de Saint-Malo et le DRASSM (Département des Recherches Archéologiques Subaquatiques et Sous-Marines, Ministère de la Culture) pour leur soutien financier.

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
Google apps