Spatial variability in precipitation has received little attention in the study of connections between climate, erosion, and tectonics. However, long-term precipitation patterns show large variations over spatial scales of ∼10 km and are strongly controlled by topography. We use precipitation rate estimates from Tropical Rainfall Measuring Mission (TRMM) satellite radar data to approximate annual precipitation over the Himalaya at a spatial resolution of 10 km. The resulting precipitation pattern shows gradients across the range, from east to west along the range, and fivefold differences between major valleys and their adjacent ridges. Basin-wide average precipitation estimates correlate well with available measured mean runoff for Himalayan rivers. Estimated errors of 15%–50% in TRMM-derived annual precipitation are much smaller than the spatial variability in predicted totals across the study area. A simple model of orographic precipitation predicts a positive relationship between precipitation and two topographically derived factors: the saturation vapor pressure at the surface and this pressure times the slope. This model captures significant features of the pattern of precipitation, including the gradient across the range and the ridge-valley difference, but fails to predict the east-west gradient and the highest totals. Model results indicate that the spatial pattern of precipitation is strongly related to topography and therefore must co-evolve with the topography, and suggest that our model may be useful for investigation of the relationships among the coupled climate-erosion-tectonic system.

A quantitative model of gneiss dome formation must account for the spontaneous development of large structural relief, relative to surface relief, at the base of the brittle layer for appropriate physical parameterization of the crustal rheology and the modification of topography by erosion. An earlier model has been augmented to include (i) crustal necking, as well as contributions to dome initiation from (ii) density instability and from (iii) an erosional law in which sinusoidal components in surface topography are amplified at wavelengths L > L * and decay for L < L *. A further modification replaces a ductile halfspace with a downward softening viscous layer resting on rigid mantle at a weak planar detachment. Necking alone predicts crustal instability for only a few candidate creep laws and maximum rock strength near the upper surface. Density instability and erosional amplification make independent, additional contributions to the strength of instability of the same magnitude as that from necking, extending the domain of dome initiation to much larger ranges in the dimensionless parameters that govern model behavior. Our results indicate that crustal extension tends to strongly localize for a broad range of rock types dominating crustal rheology, leading to crustal necks centered on large amplitude antiformal structures. The tendency for the necks to form spontaneously and amplify rapidly is strongly enhanced by a destabilizing density contrast at depth and erosional evacuation of material from the necks. The analysis shows that crustal necks with a length scale of 50–100 km, 4–5 times the thickness of the brittle crust, tend to dominate the initial structures. These are likely to develop into domal structures, river anticlines, and, more generally, zones of localized deformation and rock uplift, especially where erosion is rapid.

An extraordinary wind storm on December 20, 1977, caused moderate to severe damage to structures, crops, orchards, vehicles, wildlife, and soils in an area of about 2,000 km 2 in the Southern San Joaquin Valley, California. Wind that may locally have reached velocities of 300 km/hr mobilized more than 25 million metric tons of soil from grazing lands alone within a 24-hour period, yielding a depositional plume that extended at least to the northern end of the Sacramento Valley; comparable amounts of soil may have been displaced in adjacent agricultural lands. The wind-stripped land in the Tehachapi and San Emigdio mountains caused accelerated runoff during ensuing rainstorms that exacerbated the problem of flooding in the southern valley and initiated numerous gullies that will continue to extend the loss of soil. The principal factors contributing to the severity of the storm’s impact were drouth, overgrazing, and the general lack of windbreaks in the agricultural land. Vegetation in the grazing lands bordering the valley showed the combined stresses of drouth and grazing before the storm and provided little forage and only slight protection to the soil. Broad areas of agricultural land had recently been plowed in preparation for planting, and additional areas had been stripped of natural vegetation and leveled in preparation for agricultural uses making them vulnerable to wind erosion. Other quantitatively less important contributing factors included stripping of vegetation for urban expansion in the Bakersfield area, extensive denudation of land in the oil fields north of Bakersfield and elsewhere, and local denudation of land by récréation vehicles.