LANDSLIDES TRIGGERED BY THE MAY 1-2, 2010, STORM IN THE NASHVILLE METROPOLITAN AREA, DAVIDSON COUNTY, TENNESSEE: MAGNITUDE AND DISTRIBUTION

A record two-day storm on May 1 and 2, 2010, caused costly and deadly flooding, and also triggered hundreds of landslides in the Nashville metropolitan area (NMA). Current research objectives include assessing landslide magnitude (size and number) and distribution, hazard assessment of damaging landslides and those near critical facilities, and developing a conceptual model for landsliding in the NMA. In the Davidson County part of the NMA, preliminary mapping using post-storm aerial photography and limited field investigations have identified more than 475 landslides and other storm-related deposits. The landslides occurred on natural and modified slopes underlain by flat-lying Ordovician through Mississippian-age sedimentary rocks. Slope colluvium is locally reinterpreted as landslide deposits based on benched topography that suggests some pre-existing landslides may involve the underlying rock. Landslide types include both shallow and deep-seated debris slides, complex debris slide–debris flows, and some debris flows. The largest identified landslide is about 285 meters long, has a main scarp about 25 meters high, and formed a landslide dam. Large-displacement landslides (movement of a few meters or more) commonly toppled trees on forested slopes and are generally discernible on the aerial photography. Small-displacement landslides (movement less than a meter) have been identified only by field investigations; thus, the total number of this type of slide remains unknown. Landslide distribution is characteristically clustered with most of the landslides occurring in the southwestern and south-central parts of Davidson County. Landslides also occurred along the banks of the Cumberland River and its tributaries and in a northeast-trending belt in the northern part of the county. About 40 landslides were documented to have been triggered by a near-record storm in March 1975. The May 2010 storm triggered more and larger landslides than the March 1975 storm and the 2010 landslides were distributed over a greater part of the NMA.