The Appalachian Region encompasses the mountainous terrain stretching from Alabama to Maine and can be divided into a few different characteristic landslide mechanisms based on regional topography and geology. In the low relief Allegheny Plateau, river incision through weak Paleozoic shales leads to widespread failures that are exacerbated by development in areas like Pittsburgh and Cincinnati (Pomeroy, 1982).
In the steeper parts of the Appalachia Region (Smokies, Blue Ridge, Adirondacks, etc.), widespread landsliding occurs primarily in response to high rainfall from tropical and extratropical cyclones (Wieczorek et al. 2009; Wooten et al., 2016). For example, Hurricane Camille in 1969 triggered more than 3,000 debris flows in the Blue Ridge Mountains of Virginia following 71-80 cm of rainfall in 8 hours (Morgan et al., 1999). In the high peaks of the Adirondack Mountains, dozens of landslides following heavy rains from Hurricane Irene in 2011 led to persistent bare rock scars that remain unvegetated.
The dominant landslide mechanism in the Appalachian Region is shallow failure of soils and weathered rock in hollows that then mobilize as debris flows. This mechanism is broadly similar to debris flow initiation in the soil-mantled landscapes of the Pacific and Caribbean regions, where models like ShalStab have been used to model regional hazard. Most of Appalachia is soil-mantled heavily vegetated, and generally less steep than the Pacific or Rocky Mountain regions, leading to higher rainfall intensity-duration thresholds than elsewhere in the country (Wieczorek et al. 2009).
Three factors important to highlight for future landslide hazards. First, although the region is heavily vegetated, there has been a dramatic shift in forest composition since the early 20th century as a consequence of pests like chestnut blight and hemlock woolly adelgid. This is hypothesized to have altered root structure/cohesion (Hales et al., 2009; Wooten et al., 2016). Second, global warming has led to increased rainfall associated with tropical cyclones, with implications for extreme events. Even historically there have been extreme rainfall triggers, and likely to be more common moving forward (Ren, 2016, others). Finally, strip mining and mountain top removal has created anthropogenic landslide hazards that can be especially destructive.
There is also a strong tie-in with cascading/downstream hazards in Appalachia, and routing of sediment from debris flows is critical to understand.