Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.

[1] In mountainous landscapes the role of periglacial processes in producing sediment is poorly defined, despite evidence of abundant talus slopes. Ice growth in rock has long been recognized as an efficient erosion mechanism, but the effects have not been readily applied to landscape evolution in response to tectonic and climatic forcing. Here, we quantify how and where ice-driven mechanical erosion occurs in cold, bedrock-dominated landscapes using a simple one-dimensional numerical heat flow model. In our model, ice grows by water migration to colder regions in shallow rock by the reduction in chemical potential associated with intermolecular forces between ice and mineral surfaces, a process called segregation ice growth. The depth and intensity of frost cracking is primarily dependent on mean annual temperature (MAT), with positive MAT sites characterized by intense cracking in the top meter of the rock mass and a maximum frost penetration of $4 m. In contrast, negative MAT areas have less intense cracking that primarily occurs at depths between 50 and 800 cm. We compare the depth and intensity of frost cracking predicted by our model with measures of the intensity of frost processes determined in three studies: The first measured the timing of rockfall in the Canadian Rockies, Niagara Escarpment, and Japanese Alps; the second analyzed scree deposits in the Southern Alps, New Zealand; and the third documented rockfall frequency in Utah. These natural examples show that rockfalls tend to nucleate at elevations that coincide with zones of intense frost cracking predicted by our model. As such, climatic variations associated with interglacial-glacial cycles may impart a significant influence on the denudation of mountainous landscapes.

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[1] Shallow landslides are a significant hazard in steep, soil-mantled landscapes. During intense rainfall events, the distribution of shallow landslides is controlled by variations in landscape gradient, the frictional and cohesive properties of soil and roots, and the subsurface hydrologic response. While gradients can be estimated from digital elevation models, information on soil and root properties remains sparse. We investigated whether geomorphically controlled variations in ecology affect the spatial distribution of root cohesion by measuring the distribution and tensile strength of roots from soil pits dug downslope of 15 native trees in the southern Appalachian Mountains, North Carolina, United States. Root tensile strengths from different hardwood tree species were similar and consistently higher than the only native shrub species measured (Rhododendron maximum). Roots were stronger in trees found on noses (areas of divergent topography) relative to those in hollows (unchanneled, convergent topography) coincident with the variability in cellulose content. This cellulose variability is likely related to topographic differences in soil water potential. For all species, roots were concentrated close to the soil surface, with roots in hollows being more evenly distributed in the soil column than those on noses. Trees located on noses had higher mean root cohesion than those in hollows because of a higher root tensile force. R. maximum had the shallowest, weakest roots suggesting that recent expansion of this species due to fire suppression has likely lowered the root cohesion of some hollows. Quantification of this feedback between physiologic controls on root growth and slope hydrology has allowed us to create a curvature-based model of root cohesion that is a significant improvement on current models that assume a spatially averaged value.

The interaction of fluvial, glacial, and hillslope processes controls the development of mountain belts and their response to tectonic and climatic forcing. Studies on the contribution of hillslope processes to mountain erosion have focused on bedrock landslides, as they have a profound and readily observed impact on sediment yield and slope morphology. Despite the ubiquity of scree (or talus) mantled slopes in mountainous terrain, the role of frequent, low-magnitude (Ͻ100 m 3) rockfall events is seldom addressed in the context of landscape evolution. Here we quantify the contribution of rockfall erosion across an 80 by 40 km transect in the Southern Alps, New Zealand, by analyzing the spatial extent of scree slopes mapped from aerial photographs and estimating long-term (10-15 k.y.) rockfall erosion rates from the accumulation of slope deposits below bedrock headwalls and in debris and alluvial fans. Along the rapidly uplifting, high-rainfall western margin, where high rates of bedrock landsliding have been previously documented, scree-mantled slopes are sparse. Rainfall decreases exponentially east of the Main Divide, and the proportion of slopes mantled by scree increases monotonically, attaining a maximum value of 70%. The systematic distribution of scree deposits cannot be attributed to lithologic variation, seismicity, or the legacy of glaciation. Instead, climate may serve as a primary control on scree production, as nearly 70% of the mapped scree deposits in our transect are confined to a narrow elevation range of 1200-1600 m above sea level (masl). Our analysis of altitudinal controls on annual temperature variations indicates that scree production via frost-cracking processes may be maximized between elevations of 1600 and 2300 masl, as higher elevations are subject to persistent permafrost which obviates the frost-cracking process. Rates of rockfall erosion near the rapidly uplifting Main Divide are low (Ͻ0.1 mm/yr), whereas rates in the scree-dominated eastern areas average 0.6 mm/yr and may approximately balance rock uplift.