Ground Water at Yucca Mountain How High Can It Rise? (1992) / Chapter Skim
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Appendix C: The Effects of Pluvial Climates in the Vicinity of Yucca Mountain: A Summary
Appendix C: The Effects of Pluvial Climates in the Vicinity of Yucca Mountain: A Summary
Pages 190-211
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From page 190... ...
was among the first to correlate high stands of these lakes, and the "pluvial" climates that they indicated, with glacial ages. The correlation between pluvial climatic episodes and glacial ages (or stades)
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From page 191... ...
Other important issues have been resolved more recently, including what constitutes a pluvial climatic regime in this region, and how much of an impact do pluvial climatic episodes have in terms of increased recharge to the aquifer. The answers to these questions affect assessments of the suitability of Yucca Mountain, or any other proposed locality in the vicinity of the Nevada Test Site, as a potential subsurface repository for high-level nuclear waste.
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From page 192... ...
The widespread paleohydrologic evidence for a drier ice-age climatic regime in the vicinity of the Nevada Test Site, relative to the central and northern Great Basin, conflicts with many popular conceptions of the effect of the last pluvial episode. But there are several lines of evidence that indicate that the last pluvial climatic regime was actually relatively arid.
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From page 193... ...
, SOIL SPOILS ~::E1,~ ,£i -2 i} F ;l 6 EXTENSIVE 53 t10RE LlFtlTED it, 5 PONDS AND nARSHES AND DESICCAT1~3N MARSHES WET MEADOWS AND EROSION LAS VEGAS VALLEY RIDDERS FROM VICINITY OF NEVADA TEST SITE N= 148 .
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From page 194... ...
These assemblages are usecl to infer climatic conditions at a given time, established by radiocarbon dating organic material selected from the midclen sample. THE PALEOECOLOGICAL RECORD The paleocological record provided by both fossil pollen and plant macrofossils from radiocarbon dated packrat middens provides direct evidence of environmental conditions during the last glacial age.
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From page 195... ...
Selected Fossil Records During the last glacial age juniper woodland extended to the valley bottoms while the driest sites supported shrubs such as shaclscale (AtnpZex confertifo~ia) and sagebrush (Artemisia subgen.
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From page 196... ...
1.47 ~ 0.06 kid (LADI 11 A(t2) 36.25 ~ 0.91 ke ~ OTHER DESERT SHRUBS - 1 AND SUCCULE - S WART-DESERT SHRUBS Figure 2 Relative abundance of indicator plant taxa in samples from the Skeleton Hills-1 packrat midden, Amargosa Desert.
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From page 197... ...
19.02 ~ O.75 ke 24.4 ~ 0.76 ke ~'! \ I JUGS I · DESERT SHRUBS ~ SUCCULENTS I I = DOttINANT SPECIES WW-4D '77 ~ 0.74 ka ~ IJUOS I / WW-4E >44.6 ke _1 _n _— \ · N0 - ANE/SUBALPINE / \ [JUGS I / ~ STEPPE SHRUBS Figure 3 Relative abundance of indicator plant taxa in samples from the Willow Wash4 packrat midden, southeastern Sheep Range.
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From page 198... ...
, the major drainage of the western Nevada Test Site. The FMC-7 midden site lies at cat 1250 m elevation ant]
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From page 199... ...
20 16 12 8 4 0 ., ~ RADIOCARBON AGE ( ke ) 25 15 % OF N 10 s ~ SUNNER-FLOWERINS i RIPARIAH ~ MO~ANEJSUBALPINE Figure 4 Indicator taxa in packrat midden samples from Fortymile canyon, immediately east of North Yucca Mountain, as percentages of the total number of taxa (N)
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From page 201... ...
It currently enters North America over the Pacific Northwest, but was deflected southward during the full-glacial by the massive Laurentide ice sheet and an enhanced pole-equator pressure gradient. The fact that it may have entered the continent south of the Nevada Test Site area (Figure 5)
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From page 202... ...
Prescribed ice sheet extent indicated by hachured area, modeled mean position of the westerly jet indicated by stippled area. Arrows indicate stronger surface winds than present in winter (W)
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From page 203... ...
Despite evidence for the northward retreat of the westerly jet, effective moisture continued to exceed that of the present until the close of the early Holocene in Southern Nevada (Spaulding, 1985; Van Devender et al., 1987~. The Searles Lake and the Las Vegas Valley records even indicate episocles of increased effective moisture (Figure 1~.
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From page 204... ...
Model simulations of seasonal precipitation over an area-averaged Southwest also show increased summer precipitation beginning by 12 ka (Spaulcling and Graumlich, 1986~. Intensifiecl thermal lows would result in enhanced advective flow of maritime tropical air into the desert interior as moister, colder air would be drawn from the ocean into the region of low pressure.
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From page 205... ...
CONCLUSIONS AND INFORMATION NEEDS There is virtually no evidence in the glacial-age fossil record for an increase in average annual precipitation exceeding 40 percent of modern amounts. The nature of full-glacial vegetation can be attributed to a relatively cold and dry climatic regime with increaser]
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From page 206... ...
1976. Vascular plants of the Nevada Test Site, and central-southern Nevada.
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From page 207... ...
1989. Late Wisconsin groundwater discharge environments of the southwestern Indian Springs Valley, southern Nevada Quaternary Research.
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From page 208... ...
It is not known to occur in woodland vegetation today. However, glacial-age macrofossil assemblages indicate that, on calcareous substrate, it commonly occurred in juniper woodland.
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From page 209... ...
shared dominance with limber pine in image subalpine woodlands. Limber pine is drought tolerant, and the widespread occurrence of subalpine conifer woodland dominated by this tree, usually associated with sagebrush, indicates a relatively dry and cold climate pinyon pine (Pious morzophyZla)
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From page 210... ...
. Occasional glacial-age fossil records of this species are usually associated not with ponclerosa pine, its common modern associate, but with the subalpine conifer limber pine (Pinus flexiiis'.
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From page 211... ...
Its macrofossils have been recovered from one site, located in Fortymile Canyon immediately east of North Yucca Mountain at 1250 m elevation. The carbon isotope dates for this record are 47.2 and >52 ka, placing it well before the last glacial maximum (ca.
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