Those of you who have been following my blog about the Flinders University maritime archaeology field school in South Australia know that the students have been divided up into three groups (Red, Yellow, and Green teams). These different teams continue to rotate through three primary areas to gain a variety of experience on different kinds of maritime archaeological sites. Teams have been diving and mapping the remains of the Star of Greece shipwreck in Port Willunga, they have been recording the historic pier and baths at Victor Harbor, and have been mapping the remains of the Showboat wreck on the mud flats at Hindmarsh Island. But in addition to these three, there is another project, the magnetometer survey at Middleton Beach.
Many of those who have followed LAMP’s exploits over the years know that magnetometers are devices that can be towed behind a boat, to search a large area of the seafloor for historic shipwrecks. Magnetometers record the intensity of the earth’s magnetic field, which is distorted by the presence of ferrous material (iron or steel). Thus, a wreck with significant amounts of iron (cannons, anchors, nails or bolts) can be detected by this means.
But there are also versions of the magnetometer that can be used on land. This technology can be especially useful to locate the remains of beached shipwrecks, or wrecks that went down on shoals which have over time become islands (such is the case with Conch Island off St. Augustine).
On February 8th, I accompanied the students of Green Team as they did their part to search for the Emu, a shipwreck that wrecked in 1853 as it attempted to seek safe haven in Port Elliot. As I’ve discussed in previous posts, Port Elliot was not a very safe harbor, and the Emu was one of many ships plying that trade that went down. The Emu is especially interesting as it was built in Australia relatively early, in 1841. Historic photographs show its remains partially buried in the sand dunes at Middleton Beach, just east of Port Elliot.
Today Middleton Beach is popular with surfers and beachgoers. It boasts beautiful views of the bluffs of Port Elliot in the background. On a rough day like today, it is easy to see how a sailing ship could come to peril in these turbulent waters.


We have driven to the beach parking lot (or carpark, as they say over here) with Ian Moffit, a geophysics expert and adjunct lecturer at Flinders University. Geophysics is the study of the earth’s physical properties, and in an archaeological sense usually refers to analyzing the earth with remote sensing equipment such as magnetometers, electromagnetic conductivity survey, or ground-penetrating radar. Here Ian (at left) demonstrates the components of the University’s Geometrics 856 land magnetometer. The Green team consists of (from left to right) Agnes (“Aggy”) Milowka, David Kalinowski, and David Vanzandt.

The 856 magnetometer consists of the sensor head, affixed to the top of an aluminum pole, which is connected by cables to the mag itself, which is worn slung below the user’s chest from a backpack-like harness. Here Aggy has suited up and prepares to walk the beach.

Another important piece of equipment necessary for a mag survey is a GPS (global positioning system) receiver. On marine surveys, the GPS antenna is mounted on the boat. For a walking survey, the operator carries the GPS unit. In order to get the best possible reception from the navigational satellites overhead, we have strapped the GPS to Aggy’s hat, so it will always be constantly held at the highest point of her body.

At this point, the mag operator simply walks the beach, following a pre-determined search pattern. In our case, the students of Green Team will simply walk parallel to the water’s edge, starting at the dunes and continuing back and forth over the desired section of beach, until they reach the water’s edge. There survey lanes (each leg of their walk along the beach) are spaced about two meters apart. This is simply estimated by the walker, and they use their footprints in the sand from their previous lane to keep the lanes more or less parallel. The mag is taking a reading of the earth’s magnetic field each five seconds, and the GPS is also taking readings of the walker’s position at a faster rate.

Back in the lab, the GPS output (northing, easting, and time) will be combined with the magnetometer output (magnetic field reading in gammas and time). The two sets of data are combined in a way so that for each given second that we have GPS positional data, we will have a corresponding reading from the mag. This way, if any anomalous readings (mag readings that differ dramatically from what the earth’s magnetic field should be) are generated, the data analyst can tell exactly where those anomalies are. Here, Ian demonstrates to the students in the makeshift lab (the camp kitchen) how this process works, going step by step with his computer which is projected on the wall. Each student (including me) follows along on their own computer.

The process can be tedious, as there are many redundant lines (i.e., mag readings with no corresponding GPS locational data). These are manually removed until the two datasets are aligned. Then the combined data is fed through specialized software provided by the magnetometer manufacturer and a map is generated which shows the location of any anomalies within the search area.
Today’s survey did not turn up any significant anomalies (other than the handrail along the steps leading to the beach, and the car in the parking lot, both of which we of course ignored. But it did prove that there was no concentration of iron, and therefore no Emu shipwreck, within that section of beach. The other two teams of students will continue this survey and may yet find promising anomalies on adjacent sections of the beach. The next step would be to continue to test any such anomalies, using other remote sensing techniques such as electromagnetic conductivity testing or ground-penetrating radar. Such techniques may help confirm the presence of and determine the size and depth of buried remains. Finally, archaeological testing (excavating test units by hand) could be used to determine what actually might be buried underneath the sand.
I am particularly interested in this technology and its application, as it has been a very long time since I have used a land mag (I have actually used the Geometrics 856 back in my days at Florida State University). Back in St. Augustine, there are many potential applications for land magnetometry. We are particularly interested in testing Conch Island for the presence of buried shipwrecks. Conch Island, now part of Anastasia Island State Park, is a landform built up since 1940 over a series of shoals known historically as the North Breakers and also the Crazy Shoals. These shifting sand bars often spelled doom to ships attempting to enter or leave St. Augustine through the historical inlet, so it is virtually certain that there are shipwrecks buried here.

<1887 Coastline
This map shows the outline of the 1887 coastline of St. Augustine, superimposed with the present-day coastline (solid color). While Anastasia Island is in more or less the same position as it was in 1887, Conch Island (not actually a true island) did not exist as a landform until the 1940s.
At the recent SHA conference, I invited a friend of mine, Doug Hervoic, owner of a company called Marine Magnetics, to visit St. Augustine, and he offered the use of a Marine Magnetics land mag. So we may be doing a similar survey this March in St. Augustine. I’m glad to have had an opportunity to work with Ian on a land mag survey in Australia, just in time to prep me for our continued work back home.