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Colonial Shipwrecks of Colombia: Magnetometer Survey of Bahía de la Gloria and Isla Tarena

Archaeologist Bert Ho runs tows the magnetometer from our survey boat, while monitoring the readout and incoming results on the Panasonic Toughbook with the differential GPS mounted on a bamboo pole.
Credit: Andres Diaz/The Meadows Center for Water and the Environment at Texas State University

National Geographic Grantee and Texas State University Research Faculty Frederick “Fritz” Hanselmann and a top-notch team of archaeologists from Colombia and the United States are leading an expedition to locate and document historic shipwrecks off of the Caribbean coast of Colombia. Follow along with Fritz’s updates from the field. 

While Chris, Juan, and I were busy mapping the possible seawall in Bahía de la Gloria, Bert and Andres began the magnetometer survey in and around the bay and Isla Tarena.  Electronic survey is one of the first steps to locating potential shipwreck sites.  In areas with high rates of sedimentation such as river mouths and bays, a magnetometer is often the best tool to read into the sediment on the seafloor.   As mentioned in an earlier post during our work off of Cartagena, a magnetometer functions similar to a metal detector, but has a much higher sensitivity, able to detect large metallic signatures, or anomalies, in the magnetic signature of a given geographic region.  The magnetometer allows us to conduct geophysical and electronic mapping.  What this means for us as archaeologists is that we have a tool that is extremely useful for finding historic shipwrecks as many of them have different characteristics and features that are made of iron.  The mag is towed from the stern of the boat and the boat is driven in lanes predetermined in the GPS and survey software, which allow us to cover an area accurately and efficiently.  If you notice in the picture above, we’ve had to take a certain license to rig up our panga to function as a survey boat, yet it worked great!
Bathymetric mapping results of our initial magnetometer survey in Bahía de la Gloria.  The red indicates the possible wall. Credit: Bert Ho/The Meadows Center for Water and the Environment at Texas State University

Initial bathymetric results of our initial magnetometer survey in Bahía de la Gloria. The red indicates GPS waypoints on the possible wall.
Credit: Bert Ho/The Meadows Center for Water and the Environment at Texas State University

In the case of Bahia de la Gloria, we only have a slight idea as to the kinds of ships that have wrecked in the area, i.e.: merchant or naval vessels, but the magnetometer will help us identify areas of interest to conduct diver visual surveys and determine if there is any material culture that creates the anomaly or signature. Once we’ve surveyed an area, we process the data that we’ve acquired so that we can understand where potential cultural resources might be buried and the overall topography and bathymetry of the seafloor in a project area.  After the initial processing of the data with the few hours of electricity that we have per day, we start to plan our next dives to explore the anomalies that show up in the results.