Magnetometer survey for buried steamboats near the mouth of the Missouri river

During the early- to mid-eighteenth century hey-day of steamship navigation on the Mississippi and Missouri Rivers literally hundreds of ships were lost due to snags, explosions and collisions. Shifting river channels, especially prior to channel stabilization in the early twentieth century, has left many of the wrecks below corn fields instead of water. We conducted a reconnaissance magnetometer survey near the mouth of the Missouri River to search for four reported shipwreck sites. The magnetometer and DGPS location and guidance system were mounted on an aluminum backpack with the GPS antenna at 2 m and the magnetometer sensor at 2.3 m above ground. Approximately 370 acres were searched with a 20 m transect spacing in June, 2007, locating one large magnetic anomaly within 100 m of one reported shipwreck location. A more detailed assessment of this anomaly using 5 m transect spacing revealed it to be 50 m in diameter and 102 nT maximum amplitude. This magnetic anomaly is consistent with an 8 to 10 ton iron object buried 13 m below ground. Further investigation of the site of this magnetic anomaly is recommended.