Geophysical surveys at Formoso underwater archaeological stilt village in the eastern Amazon region, Brazil.

Archaeological evidence of pre-colonial indigenous villages are scarce in the Amazon region. Normally, wood decomposes quickly in the ground. However, in the case of stilt houses, the archaeological materials can be well preserved underwater or buried in sediments below waterbodies. The main objective of this work is to advance the understanding about the archaeological stilt village at the Formoso Lake in the Maranhão wetland, eastern Brazilian Amazon. We applied Ground Penetrating Radar (GPR) and Side Scan Sonar (SSS) for this underwater archaeological investigation. The GPR results allowed us to map the lakebed and detect diffraction hyperbolas in the water column, which can be related to wood stilts. The SSS results also helped image the lakebed and identify stilts with a higher spatial coverage compared to GPR. The combination of these two non-invasive geophysical methods allowed us to detect stilts beyond the area found in previous studies. These findings can guide the search and collection of new archaeological materials and, therefore, contribute to preserving this unique cultural heritage.