Archaeological investigation into the transportation of basalt logs to Nan Madol
The SC-098 Survey of Science, fall class 2012, went to Nett Point to carry out an archeological engineering experiment. The main hypothesis was that ancient Pohnpeian engineers may have moved basalt logs in shallow sea water by inverting their canoes, attaching a strong frame, and then lashing a basalt log to the apparatus. Additionally, it was also speculated that the basalt log was suspended under the raft and in the water. In this way, the upward buoyant force of water could reduce the weight of the basalt log and, as the raft moved through the water, this motion would also increase stability of the raft. The experiment at Nett Point also served as a teaching demonstration to reinforce the concept of the scientific method as well as to illustrate the function of force diagrams used in physics. Both these concepts are topics in the Survey of Science class.
The experiment at Nett Point was a preliminary experiment to test feasibility of the idea. Three plastic bins and a frame, made from wooden 2x4s, were lashed together with rope. The raft was placed in the water and the weights (a safe substitute for basalt rock) added to it - one by one.
From left to right: Rayches Eperiam, Kendan Paul, and Dr. Lefric Enwall securing the frame to the plastic bins.
From left to right: Kendan Paul, Maridell Edwin, Yolima Yoma, and Aiko Jack adding the final weights to the raft.
By inverting the plastic bins an effect similar to lift bags, commonly used by salvage companies, could be achieved. The experimental raft was able to hold approximately 440 lbs. (200kg) with room to spare. Additionally, the raft was towed slowly to demonstrate the increased stability of the raft and the submerged weights. In the second experiment, where the weight was placed above the water, the raft effectively sank with only about 297 lbs. (135 kg). Also, stability could not be achieved except by having people physically hold the raft in place.
The experimental raft being towed to demonstrate stability.
The experimental raft was successful in demonstrating that a significant weight could be carried by using inverted objects to trap the air and by submerging the weight in the water. While the experiment does not prove how the ancient Pohnpeians moved the basalt stones, it offers a possible solution as to how they might have moved such massive stones to Nan Madol. Using this preliminary example, it might be possible to secure funding for a scale up experiment using real canoes and a basalt log weighing 1000 kg.
On the educational level, it is hoped that exposing students to real world experiments not only reinforces classroom concepts but also lets them see that science is something they can do and not always something done by “other people.”
The SC-098 Survey of Science (Fall 2012) students participating in the experiment.
The equipment was generously provided by COM-Pohnpei campus. Thanks to Adleen Shed and Edwin Sione for helping get all the equipment together for the experiment. Thanks to Xavier Yarofmal and Salba Silbamuz for use of the wood shop and the wood for the raft. Thank you to Cindy McCord for taking all the photos. And also a huge thanks to Alden Lorens, one of the students, for giving the soaking wet students a ride home. Dr. Lefric Enwall is a World Teach volunteer teaching science and health at the Pohnpei campus.