Metamorphism in allochthonous and autochthonous terranes of the western United States

1990 ◽  
Vol 331 (1620) ◽  
pp. 549-570 ◽  
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Western United States ◽  
Metamorphic Overprint ◽  
Late Mesozoic ◽  
Lithic Assemblages ◽  
Wide Range ◽  
Uplift And Erosion ◽  
Great Valley

The haphazard accretion of exotic terranes during continental reassembly results in a crustal college typified by genetically unrelated lithotectonic belts. Profound chronologic, lithologic, geochemical, and metamorphic breaks characterize such suture zones. However, post-metamorphic differential vertical uplift and erosion can generate a marked discontinuity in grade within a single lithotectonic entity, and in contrast, post-amalgamation recrystallization of an exotic terrane assembly can produce an isofacial metamorphic overprint. Thus the tectonic context of metamorphic mineral parageneses must be interpreted with caution. In spite of the presence of allochthonous terranes, the western U.S. Cordillera in general is characterized by gradual sectorial enlargements towards the modern edge of the continent, by coherent, broadly continuous isotopic or geochemical provinces, and by systematic oceanward decreases in the metamorphic intensities of the constituent lithic assemblages, both within a belt, and across a series of belts. These relationships hold over a wide range of scales, from that of a physiographic province to that of a quadrangle-sized area. Examples described include chronologic, isotopic, igneous and metamorphic belts of (1) the entire western conterminous U.S. Cordillera, (2) the Phanerozoic Sierran-Klamath basement terrane assembly, and (3) the Great Valley and Franciscan sedimentary couplet derived from the late Mesozoic Sierra Nevada-TClamath arc. For these cases, systematic recrystallization-deformation trends and nearly in situ growth of sialic crust are evident. Mapped metamorphic and structural discontinuities reflect dislocations involving spatially associated, co-evolving continental lithotectonic units, and, except for fartravelled oceanic fragments, do not imply wholesale juxtaposition of exotic, genetically unrelated terranes.

scholarly journals Influence of Atmospheric Rivers on Mountain Snowpack in the Western United States

2018 ◽  
Vol 31 (24) ◽  
pp. 9921-9940 ◽  
Author(s):  
N. Goldenson ◽  
L. R. Leung ◽  
C. M. Bitz ◽  
E. Blanchard-Wrigglesworth
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Snow Water Equivalent ◽  
Region Of Interest ◽  
Internal Variability ◽  
Western United States ◽  
Historical Period ◽  
Atmospheric Rivers ◽  
Atmospheric River ◽  
The Impact

In the coastal mountains of western North America, most extreme precipitation is associated with atmospheric rivers (ARs), narrow bands of moisture originating in the tropics. Here we quantify how interannual variability in atmospheric rivers influences snowpack in the western United States in observations and a model. We simulate the historical climate with the Model for Prediction Across Scales (MPAS) with physics from the Community Atmosphere Model, version 5 [CAM5 (MPAS-CAM5)], using prescribed sea surface temperatures. In the global variable-resolution domain, regional refinement (at ~30 km) is applied to our region of interest and upwind over the northeast Pacific. To better characterize internal variability, we conduct simulations with three ensemble members over 30 years of the historical period. In the Cascade Range, with some exceptions, winters with more atmospheric river days are associated with less snowpack. In California’s Sierra Nevada, winters with more ARs are associated with greater snowpack. The slope of the linear regression of observed snow water equivalent (SWE) on reanalysis-based AR count has the same sign as that arrived at using the model, but is statistically significant in observations only for California. In spring, internal variance plays an important role in determining whether atmospheric river days appear to be associated with greater or less snowpack. The cumulative (winter through spring) number of atmospheric river days, on the other hand, has a relationship with spring snowpack, which is consistent across ensemble members. Thus, the impact of atmospheric rivers on winter snowpack has a greater influence on spring snowpack than spring atmospheric rivers in the model for both regions and in California consistently in observations.

Isozyme structure of Peridermium harknessii in the western United States

1991 ◽  
Vol 69 (11) ◽  
pp. 2434-2441 ◽  
Author(s):  
D. R. Vogler ◽  
B. B. Kinloch Jr. ◽  
F. W. Cobb Jr. ◽  
T. L. Popenuck
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Rust Fungus ◽  
Western United States ◽  
Population Genetic Study ◽  
Coastal Forests ◽  
Low Frequencies ◽  
Heterozygous Condition ◽  
Pinus Spp ◽  
Pine Species

We conducted a population genetic study of the western gall rust fungus (Peridermium harknessii) using isozymes as genetic markers. Electrophoresis of 341 single-gall aeciospore isolates collected from several pine species revealed that western gall rust is comprised of two distinct zymodemes (multilocus electrophoretic types) in the western United States. Within zymodemes, all 15 loci studied were monomorphic (0.95 criterion), although variants were found at low frequencies (≤ 0.03) at 3 loci. Zymodeme I was characterized by single bands, indicating homozygosity at all loci; it consisted of isolates from all pine species and environments studied, including the Pacific Coast and Cascade Ranges and the Sierra Nevada and Rocky Mountains. Zymodeme II, which was absent from coastal forests, was characterized by double or triple bands at 6 of 15 loci. The additional bands were interpreted as products of alternative alleles in heterozygous condition; isozyme phenotypes at the other nine loci were identical to those of zymodeme I. Presumed heterozygotes were fixed within zymodeme II, and homozygotes of alleles unique to this zymodeme were not found. Generally, all isolates sampled from a forest stand were in the same zymodeme, and when isolates from both zymodemes were found in the same location, recombinant genotypes between zymodemes were not observed. Such extreme disequilibrium is inconsistent with sexual reproduction, indicating that P. harknessii is asexual. Key words: western gall rust, Pinus spp., genetic variation.

scholarly journals Characteristics of dust storm events over the western United States

2013 ◽  
Vol 13 (5) ◽  
pp. 14195-14220 ◽  
Author(s):  
H. Lei ◽  
J. X. L. Wang
Keyword(s):  
United States ◽  
Dust Storm ◽  
Dust Storms ◽  
Satellite Observations ◽  
Western United States ◽  
Storm Events ◽  
Cold Fronts ◽  
Deep Blue ◽  
Modis Aod

Abstract. In order to better understand the characteristics of dust storm processes over the western United States, available dust storm events reported by media or recorded by NASA earth observatory are classified into four types based on the prevailing weather systems. Then these four types of dust storm events related to cold fronts, downbursts, tropical disturbances, and cyclogenesis and their selected typical representative events are examined to explore their identifiable characteristics based on in-situ and remote sensing measurements. We find that the key feature of cold front-induced dust storms is their rapid process with strong dust emissions. Events caused by rapid downbursts have the highest rates of emissions. Dust storms due to tropical disturbances show stronger air concentrations of dust and last longer than those caused by cold fronts and downbursts. Finally, dust storms caused by cyclogenesis last the longest. The analysis of particulate matter records also shows that the relative ratio of PM10 (size less than 10 μm) values on dust storm-days to non-dust storm-days is a better indicator of event identification compared to previous established indicators. Moreover, aerosol optical depth (AOD) measurements from both in-situ and satellite datasets allow us to capture dust storm processes. We show that MODIS AOD retrieved from the deep blue data better identify dust storm-affected areas and the spatial extension of event intensity. Our analyses also show that the variability in mass concentrations during dust storm processes captured only by in-situ observations is consistent with the variability in AOD from stationary or satellite observations. The study finally indicates that the combination of in-situ and satellite observations is a better method to fill gaps in dust storm recordings.

Water and Food in the American West

2018 ◽  
pp. 320-343
Author(s):  
Josué Medellín-Azuara ◽  
Jay Lund ◽  
Daniel A. Sumner
Keyword(s):  
United States ◽  
Global Economy ◽  
American West ◽  
Short Review ◽  
The United States ◽  
Western United States ◽  
Water Shortages ◽  
Groundwater Overdraft ◽  
Wide Range

The American West, the last region in the continental United States to be developed for extensive agriculture, is characterized by a wide range of biomes including arid, and semiarid regions, forest, and coastline. In its less water-rich places, this has forced the development of water supply infrastructure for agriculture and cities. The American West rapidly became an agricultural powerhouse to the United States and a major exporter of agricultural commodities in global economy. This chapter reviews agriculture in the western United States, followed by a short review of major western water issues for agriculture, including surface water shortages from drought and persistent groundwater overdraft. The California 2012–2016 drought is used as a case study to identify lessons for future food and fiber production in California, the western United States, and globally.

scholarly journals Our Skill in Modeling Mountain Rain and Snow is Bypassing the Skill of Our Observational Networks

2019 ◽  
Vol 100 (12) ◽  
pp. 2473-2490 ◽  
Author(s):  
Jessica Lundquist ◽  
Mimi Hughes ◽  
Ethan Gutmann ◽  
Sarah Kapnick
Keyword(s):  
Western United States ◽  
Atmospheric Models ◽  
Annual Average ◽  
Mountain Terrain ◽  
Wide Range ◽  
Average Precipitation ◽  
Spatial Estimates ◽  
Radar Satellite ◽  
Better Than

Abstract In mountain terrain, well-configured high-resolution atmospheric models are able to simulate total annual rain and snowfall better than spatial estimates derived from in situ observational networks of precipitation gauges, and significantly better than radar or satellite-derived estimates. This conclusion is primarily based on comparisons with streamflow and snow in basins across the western United States and in Iceland, Europe, and Asia. Even though they outperform gridded datasets based on gauge networks, atmospheric models still disagree with each other on annual average precipitation and often disagree more on their representation of individual storms. Research to address these difficulties must make use of a wide range of observations (snow, streamflow, ecology, radar, satellite) and bring together scientists from different disciplines and a wide range of communities.

scholarly journals Short-Range Probabilistic Quantitative Precipitation Forecasts over the Southwest United States by the RSM Ensemble System

2007 ◽  
Vol 135 (5) ◽  
pp. 1685-1698 ◽  
Author(s):  
Huiling Yuan ◽  
Steven L. Mullen ◽  
Xiaogang Gao ◽  
Soroosh Sorooshian ◽  
Jun Du ◽  
...  
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Great Basin ◽  
Stage Iv ◽  
Ensemble Forecasts ◽  
Southwest United States ◽  
Marked Variability ◽  
Wide Range ◽  
Quantitative Precipitation Forecasts ◽  
Environmental Prediction

Abstract The National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) is used to produce twice-daily (0000 and 1200 UTC), high-resolution ensemble forecasts to 24 h. The forecasts are performed at an equivalent horizontal grid spacing of 12 km for the period 1 November 2002 to 31 March 2003 over the southwest United States. The performance of 6-h accumulated precipitation is assessed for 32 U.S. Geological Survey hydrologic catchments. Multiple accuracy and skill measures are used to evaluate probabilistic quantitative precipitation forecasts. NCEP stage-IV precipitation analyses are used as “truth,” with verification performed on the stage-IV 4-km grid. The RSM ensemble exhibits a ubiquitous wet bias. The bias manifests itself in areal coverage, frequency of occurrence, and total accumulated precipitation over every region and during every 6-h period. The biases become particularly acute starting with the 1800–0000 UTC interval, which leads to a spurious diurnal cycle and the 1200 UTC cycle being more adversely affected than the 0000 UTC cycle. Forecast quality and value exhibit marked variability over different hydrologic regions. The forecasts are highly skillful along coastal California and the windward slopes of the Sierra Nevada Mountains, but they generally lack skill over the Great Basin and the Colorado basin except over mountain peaks. The RSM ensemble is able to discriminate precipitation events and provide useful guidance to a wide range of users over most regions of California, which suggests that mitigation of the conditional biases through statistical postprocessing would produce major improvements in skill.

Contemporary uplift of the Sierra Nevada, western United States, from GPS and InSAR measurements

Geology ◽  
2012 ◽  
Vol 40 (7) ◽  
pp. 667-670 ◽  
Author(s):  
W. C. Hammond ◽  
G. Blewitt ◽  
Z. Li ◽  
H.-P. Plag ◽  
C. Kreemer
Keyword(s):  
United States ◽  
Sierra Nevada ◽  
Western United States

scholarly journals Assessing differences in snowmelt-dependent hydrologic projections using CMIP3 and CMIP5 climate forcing data for the western United States

2015 ◽  
Vol 47 (2) ◽  
pp. 483-500 ◽  
Author(s):  
Darren L. Ficklin ◽  
Sally L. Letsinger ◽  
Iris T. Stewart ◽  
Edwin P. Maurer
Keyword(s):  
United States ◽  
River Basin ◽  
Sierra Nevada ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Western United States ◽  
Recent Climate ◽  
High Emission ◽  
And Shifts

Most recent climate change impact studies are using Coupled Model Intercomparison Project Phase 5 (CMIP5) projections to replace older generation CMIP3 projections. Here we evaluate whether differences between projections based on comparable high emission pathways of a seven-member general circulation model CMIP3 versus CMIP5 ensemble change our understanding of the expected hydrologic impacts. This work focuses on the important snowmelt-dominated mountain runoff-generating regions of the western United States (WUS; Upper Colorado River Basin (UCRB), Columbia River Basin (CRB), and Sierra Nevada (SN) Basins). Significant declines in snowmelt, and shifts in streamflow timing owing to warmer, wetter CMIP5 projections match or exceed those based on CMIP3 throughout the WUS. CMIP3- and CMIP5-based projections, while generally in agreement about hydroclimatic changes, differ in some important aspects for key regions. The most important is the UCRB, where CMIP5-based projections suggest increases in future streamflows. Comparable hydrologic projections result from similar underlying climate signals in CMIP3 and CMIP5 output for the CRB and SN, suggesting that previous work completed in these basins based on CMIP3 projections is likely still useful. However, UCRB hydrologic projections based on CMIP5 output suggest that a re-evaluation of future impacts on water resources is warranted.

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