“LEGACY ISLANDS”- UNINTENTIONAL ANTHROPOGENIC ARTIFACTS FORMING IN THE SUSQUEHANNA RIVER (NORTH BRANCH)

“Legacy Islands” formed in the Susquehanna River from both glacial and legacy sediments deposited upstream from manmade fish weirs. These islands are distinct from other alluvial islands due to their low elevation, V-shaped structure, sparse vegetation, and length to width ratio. The name “Legacy Islands” is proposed here to describe these landforms due to their anthropogenic origin.

Aerial imagery (1939-present) was used to locate buried fish weirs where islands formed. This study examined an unnamed island near Beach Haven, PA in the North Branch of the Susquehanna River. It was surveyed, and sediment cores were drilled to determine the stratigraphy. Samples were analyzed for grain size, mineralogy, and chemistry. Sand to sandy loam was deposited on top of medium to coarse-grained gravel; the gravel represents high-energy flood events. This sediment was periodically rooted between floods. The finest sediment (clay and silt) was composed of vermiculite, chlorite, muscovite, and quartz. Sand size sediments potentially associated with glaciation consisted of quartz, quartz with magnetite inclusions, andradite, pyrope, chromite, ferroan enstatite, spinel, zircon, and magnetite. Sand size sediments from coal production included anthracite coal, magnetic glass, metallic industrial waste, shale fragments, ferric oxyhydroxide, hematite, and coke. The distribution of fine grain sizes corresponded to trends observed in some of the major oxides (Fe₂O₃, K₂O, Na₂O, MgO, and TiO₂). Increases in these major oxides may be due to high water levels or hydromorphic processes. This is represented by mottled and iron-rich layers in the cores.

Historical aerial images help resolve how these islands form: 1. gravel bars may form upstream from fish weirs, 2. vegetation colonizes gravel and may trap sediment, allowing the island to stabilize, and 3. significant floods may reset the process. There may be more “Legacy Islands” in the Susquehanna, and they may not be restricted to this river. Despite being an unintentional manmade feature comprised of mining waste, these islands provide a valuable habit for many types of organisms. These habits may be threatened by future global climate change due to stronger flood and weather events.