Annual layer analysis in two stalagmites collected from Spring Valley Caverns, southeastern Minnesota, reveals hydrological response of the cave to extreme rainfall events in the Midwest, USA. Cave-flooding events are identified within the two samples by the presence of detrital layers composed of clay sized particles. Comparison with instrumental records of precipitation demonstrates a strong correlation between these cave-flood events and extreme rainfall observed in the Upper Mississippi Valley. A simple model is developed to assess the nature of rainfall capable of flooding the cave. The model is first calibrated to the last 50-yr (1950-1998 A.D.) instrumental record of daily precipitation data for the town of Spring Valley and verified with the first 50. yr of record from 1900 to 1949 A.D. Frequency analysis shows that these extreme flood events have increased from the last half of the nineteenth century. Comparison with other paleohydrological records shows increased occurrence of extreme rain events during periods of higher moisture availability. Our study implies that increased moisture availability in the Midwestern region, due to rise in temperature from global warming could lead to an increase in the occurrence of extreme rainfall events.
Bibliographical noteFunding Information:
This work was supported by Gary Comer Science and Education Foundation Grant CC8 , National Science Foundation Grant EAR-0902867 , GSA Research Fellowship , University of Minnesota Dennis and Emmons Fellowship . This work was also partially supported by NSF grant No. EAR-0941666 and by funds from George and Orpha Gibson for the Hydrogeology and Geofluids Research Group. We thank John Ackerman, the owner of Spring Valley Caverns, for donating the stalagmites to E. Calvin Alexander, Jr. for scientific study and his continued support of research in Spring Valley Caverns. Scott Alexander's valuable and insightful inputs are greatly acknowledged. We gratefully acknowledge Luis Gonzalez for sharing his methodology of confocal laser microscopy. S.D. thanks Shameek Bose for help with Matlab codes. Finally, we thank the two anonymous reviewers for their insightful comments that helped to improve the manuscript.
- Cave flooding
- Confocal microscopy
- Extreme rainfall events
- Fluorescent bands