Is erosion important to the structural and petrological evolution of mountain belts? The nature of active metamorphic massifs colocated with deep gorges in the syntaxes at each end of the Himalayan range, together with the magnitude of erosional fluxes that occur in these regions, leads us to concur with suggestions that erosion plays an integral role in collisional dynamics. At multiple scales, erosion exerts an influence on a par with such fundamental phenomena as crustal thickening and extensional collapse. Erosion can mediate the development and distribution of both deformation and metamorphic facies, accommodate crustal convergence, and locally instigate high-grade metamorphism and melting.

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A rock glacier-year, with little evidence of long-term surges. Different parts of the slope like boulder deposit on the Table Cliffs Plateau, Utah, has moved slowly over a long period of time and has affected over 220 trees growing on it. Analyses of annual rings of trees affected by this and other slope movements show events such as inclination, shear, corrasion, burial, exposure, inundation, and nudation. Datable responses to these events are reaction-wood growth, growth suppression and release, ring termination and new callous growth, sprouting, succession, and miscellaneous structural and morphological changes. Various events may produce delayed, antagonistic, interfering, or irrelevant event responses, necessitating procedural caution. A modified skeleton plot of yearly event responses was constructed for each sample in this study with only strongly replicating dates from within trees considered valid. The resulting event-response curve shows peak periods of movement centered around the years 1781, 1803, 1827, 1849, 1869, 1885, 1890, 1907, 1910, 1923, 1938, 1942, 1944, and 1958. Spectral analysis of the event-response curve, mean annual precipitation, and an independently derived tree-ring precipitation surrogate suggests a possible relation between precipitation and slope movement. Analyses of temperature data did not produce results in spite of the presence of internal ice which might be expected to contribute to movement. Map plots of movement through time show event responses scattered in linear zones throughout the slope during main episodes of movement in any given move at different times and some parts move more than others.

Abstract. Within the syntaxial bends of the India-Asia collision the Himalaya terminate abruptly in a pair of metamorphic massifs. Nanga Parbat in the west and Namche Barwa in the east are actively deforming antiformal domes which expose Quaternary metamorphic rocks and granites. The massifs are transected by major Himalayan rivers (Indus and Tsangpo) and are loci of deep and rapid exhumation. On the basis of velocity and attenuation tomography and microseismic, magnetotelluric, geochronological, petrological, structural, and geomorphic data we have collected at Nanga Parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the Indus and Tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes. The localization of this phenomenon at the terminations of the Himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics.

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