Magnetic detection of paleoflood layers in stalagmites and implications for historical land use changes

• Published in: Earth and planetary science letters Vol. 530; p. 115946
• Main Authors: Feinberg, J.M., Lascu, I., Lima, E.A., Weiss, B.P., Dorale, J.A., Alexander, E.C., Edwards, R.L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-01-2020
• Subjects: flood recurrence; mineral magnetism; scanning SQUID microscopy; speleothem; mineral magnetism; speleothem; scanning SQUID microscopy; flood recurrence
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2019.115946

•We image paleoflooding events in stalagmites using scanning magnetic microscopy.•This approach compiles recurrence histories of extreme paleo-precipitation events.•Case study: Mean recurrence rates are ≤5 events per century for the last 500 years in SE Minnesota.•Flooding recurrence rates increase to 7 events per century during the last 100 years.•Land use changes increased the cave's hydrogeologic response rate, carrying more fine sediment.
Flooding events are major natural hazards that present significant risk to communities worldwide. Calculations of flood recurrence rate through time are important tools for regulating land use, determining insurance rates, and for the design and construction of levees and dams. Typically, flood recurrence rates are based on limited historical data or on evidence preserved in the geologic record as overbank deposits, tree ring scars, or high water scour marks. However, these approaches are either limited in their ability to produce continuous time series of flooding events or do not consider the effects of regional land use change. Here we use scanning superconducting quantum interference device (SQUID) microscopy to rapidly image the magnetization associated with flood layers in a polished surface of an annually laminated stalagmite from Spring Valley Caverns (SVC) in southeastern Minnesota. A time series of magnetization peaks, each of which corresponds to a flooding event, yields an average flood recurrence rate of ≤5 events per century for the last 500 years. This rate increases to ∼7 events per century since 1900, coincident with historical timber and agricultural land-use changes in Minnesota. This approach produces a continuous record of well-dated, extreme-precipitation events that can be examined within the context of land use change.