[1] Snow cover duration in a seasonally snow covered mountain range (San Juan Mountains, USA) was found to be shortened by 18 to 35 days during ablation through surface shortwave radiative forcing by deposition of disturbed desert dust. Frequency of dust deposition and radiative forcing doubled when the Colorado Plateau, the dust source region, experienced intense drought (8 events and 39-59 Watts per square meter in 2006) versus a year with near normal precipitation (4 events and 17-34 Watts per square meter in 2005). It is likely that the current duration of snow cover and surface radiation budget represent a dramatic change from those before the widespread soil disturbance of the western US in the late 1800s that resulted in enhanced dust emission. Moreover, the projected increases in drought intensity and frequency and associated increases in dust emission from the desert southwest US may further reduce snow cover duration.Citation: Painter, T.

No abstract

No abstract

Pliocene (ca. 3.5 Ma) removal of dense eclogitic material under the Sierra Nevada has been proposed from variations in the petrology and geochemistry of Neogene volcanic rocks and their entrained xenoliths from the southern Sierra. The replacement of eclogite by buoyant, warm asthenosphere is consistent with present-day seismologic and magnetotelluric observations made in the southern Sierra. A necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase. An increase in potential energy should increase extensional strain rates in the area. If these forces are insuffi cient to signifi cantly alter Pacifi c-North American plate motion, then increased extensional strain rates in the vicinity of the Sierra must be accompanied by changes in the rate and style of deformation elsewhere. Changes in deformation in California and westernmost Nevada agree well with these predictions. Existing geologic evidence indicates that a period of rapid uplift along the Sierran crest of more than ~1 km occurred between 8 and 3 Ma, most likely as a consequence of removal of lower lithosphere. About this same time, extensional deformation was initiated within ~50 km of the eastern side of the Sierra (5-3 Ma), and regional shortening began to produce the California Coast Ranges (5-3 Ma). We suggest that these events were induced by the >1.2 × 10 12 N/m increase of gravitational potential energy generated by the Sierran uplift. Evidence for Pliocene uplift, adjoining crustal extension, and shortening in directly opposing parts of the Coast Ranges is found along nearly the entire length of the Sierra Nevada and implies that lithosphere was removed beneath all of the presentday mountain range. The uplifted area lies between two large, upper-mantle, high-Pwave-velocity bodies under the south end of the San Joaquin Valley and the north end of the Sacramento Valley. These high-velocity bodies plausibly represent the present position of material removed from the base of the crust. Lithospheric removal may also be responsible for shifting of the distribution of transform slip from the San Andreas Table 1) where estimates have been made of the timing of initial extension, the western edge of extension at ca. 5 Ma (thick purple line) and ca. 3 Ma (thick red line), the location of fl oras showing possible uplift (blue dots: T-Table Mountain and W-Webber Lake localities of Wolfe et al. [1998, 1997]), and the extent of tilted Miocene sedimentary rocks along the Sierra/ Great Valley margin (hatched area). The geology in the Sierra is shown in B (after Wakabayashi and Sawyer, 2000) along with the location of the ancestral Yuba River channel plotted in Figure 3 (thin red line) and the positions (bold letters) of other paleochannels plotted in Figure 3: M-Mokelumne River; S-Stanislaus River; and T-Tuolumne River. The position of the Gorda plate's southern edge relative to the Sierra at different times in the past lies along the green lines (from Atwater and Stock, 1998) assum...