Lake-Level Variation in the Lahontan Basin for the Past 50,000 Years L. V BENSON*
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QUATERNARY RESEARCH 28, 69-85 (1987) Lake-Level Variation in the Lahontan Basin for the Past 50,000 Years L. V BENSON* AND R. S. THOMPSONIJ *U.S. Geological Survey, Geological MS 404, Denver Federal Center, Denver, Sciences, Brouw University, Providence, Colorado Rhode 80225; and fDepartment Island 02912 of Received October 27, 1986 Selected radiocarbon data on surficial materials from the Lahontan basin, Nevada and California, provide a chronology of lake-level variation for the past 50,000 yr. A moderate-sized lake connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, the Pyramid Lake subbasin, and the Winnemucca Dry Lake subbasin) from about 45,000 to 16,500 yr B.P. Between 50,000 and 45,000 yr B.P., Walker Lake rose to its sill level in Adrian Valley and spilled to the Carson Desert subbasin. By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m above sea level, where it remained for 3500 yr. By 16,000 yr BP, lake level in the western Lahontan subbasins had fallen to 1240 m. This recession appears synchronous with a desiccation of Walker Lake; however, whether the Walker Lake desiccation resulted from climate change or from diversion of the Walker River is not known. From about 15,000 to 13,500 yr B.P., lake level rapidly rose, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand altitude of 1330 m by 13,500 yr BP., a condition that persisted until about 12,500 yr B.P., at which time lake level fell 2 100 m. No data exist that indicate the level of lakes in the various subbasins between 12,008 and 10,000 yr B.P. During the Holocene, the Lahontan basin was the site of shallow lakes, with many subbasins being the site of one or more periods of desiccation. The shape of the lake-level curve for the three western subbasins indicates that past changes in the hydrologic balance (and hence climate) of the Lahontan basin were large in magnitude and took place in a rapid step-like manner. The rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream, as it was forced north or south by the changing size and shape of the continental ice sheet. 0 1987 University of Washington. INTRODUCTION During the last 3 decades, various investigators have attempted to assign an absolute time scale to the last major lake cycle that occurred in the Lahontan basin in Nevada and California. The first systematic application of the radiocarbon method was by Broecker and his colleagues (Broecker and Orr, 1958; Broecker and Walton, 1959; Broecker and Kaufman, 1965). Morrison and Frye (1965) questioned the applicability of the radiocarbon method to studies of prehistoric lake levels, by pointing out that certain of Broecker’s radiocarbon dates on tufas were reversed in relation to Morrison’s (1964) stratigraphic assignments. In later years, Benson (1978, 1981) developed an alternative lake-level chronology for the Pyramid and Walker Lake subbasins of the Lahontan basin that employed a sample-selection procedure which tended to eliminate a large part of the uncertainty caused by the introduction of secondary carbon into tufa samples. This report presents a selection of new and previously published radiocarbon ages of surficial materials from the Lahontan basin, including data compiled by Thompson et al. (1986). This collection is intended to represent not the most comprehensive, but the most reliable, set of available radiocarbon-age determinations. With this data set, a model chronology of lakelevel variation, based on radiocarbon and uranium series-dated samples from three adjoining subbasins (Pyramid Lake, Winnemucca Dry Lake, and Smoke Creek- r Present address: U.S. Geological Survey, MS 919, Denver Federal Center, Denver, Colorado 80225. 69 0033-5894187 $3.00 Copyright 0 1987 by the University of Washington. All rights of reproduction in any form reserved. BENSON AND THOMPSON 70 Black Rock Desert subbasins), was derived and compared to lake-level data sets for other Lahontan subbasins for the past 50,000 yr. SURFACE HYDROLOGY BASIN BATHYMETRY AND The bathymetry of the Lahontan basin is discussed in Benson and Mifflin (1986). Lake Lahontan, at its highest stage (13,000 1210 120' 1190 yr ago), had a surface area of 22,300 km2, a volume of 2020 km3, and a maximum depth of 276 m in the Pyramid Lake subbasin. The Lahontan basin consists of seven subbasins separated by sills of varying altitude (Fig. 1; Table 1). A sill is the lowest point on the divide separating adjoining subbasins. Some subbasins (e.g., Pyramid Lake subbasin, Fig. 1) are fed by perennial streams, such that lakes in these subbasins 1160 I ORliGON 116O 1170 / -i IDAHO w--e- 42' ’ N EXPLANATION PRIMARY SILLS SECONDARY SILLS PRESENT LAND DAY LAKES AREAS PRIMARY SILLS Pronto Chocolate Adrian Valley L Darwin Pass Mud Lake Slough Astor Pass Emerson Pass MAJOR Smoke Black SUBBASINS Creek/ Rock Desert Carson Desert Buena Vista Walker Lake Pyramid Lake Winnemucca Dry Honey Lake 8 , ,, ,, ,, , , l;O Lake KILOMETERS 50 MILES I I I I 1. Map showing surface extent of Lake Lahontan 14,000 to 12,500 yr B.P. and location of subbasins and sills separating subbasins (from Benson and Mifflin, 1986). FIG. FLUCTUATIONS OF LAKE TABLE 1. ALTITUDES OF PRIMARY SILLS IN MAJOR SUBBASINS IN THE LAHONTAN BASIN (FROM BENSON AND MIFFLIN, 1986) Sill altitude (m) Sill Present day (1985) Corrected for isostatic rebound and tilting Adrian Valley Pronto Darwin Pass Chocolate Astor Pass Emerson Pass Mud Lake Slough 1308 1292 1265 1262 1222 1207 1177 1302 1283 1253 1253 1213 1195 1177 rise and fall with change in climate, while other subbasins receive water only when an adjoining subbasin fills and spills (e.g., Buena Vista subbasin). The six subbasins that form a ring (all subbasins except Walter Lake subbasin) will be referred to as the central basin in this paper. Four of these subbasins (Smoke Creek-Black Rock Desert subbasin, Honey Lake subbasin, Pyramid Lake subbasin, and Winnemucca Dry Lake subbasin) will be referred to as western Lahontan subbasins. Of the six rivers that terminate in Lahontan subbasins, four rivers (Truckee, Carson, Walker, and Humboldt) contribute 96% of the total gauged surface inflow (Benson, 1986). For the most part, the climate in the watershed area of the bordering mountain range, not the climate in the basin floor, controls fluid input to a subbasin. This control is the result of the pronounced orographic effect on precipitation in the Great Basin (Maxey and Eakin, 1949). Topography of a subbasin also influences the magnitude of lake-level change. Small narrow subbasins fed by perennial streams will, in terms of lake level, respond in a sensitive manner to changes in moisture storage (influx minus evaporation). Such subbasinal lake systems (e.g., Walker Lake) are potentially excellent recorders of 71 LAHONTAN high-frequency low-amplitude changes in climate on the subregional scale. Lakes fed by perennial streams in large wide subbasins (e.g., Pyramid Lake) respond slowly to changes in moisture storage. These systems tend to be better recorders of highamplitude climatic events. The start of lake-level rise in a subbasin that receives surface inflow by spill from an adjoining basin will lag the onset of lakelevel change in the adjoining subbasin by the amount of time it takes the adjoining subbasin to fill to sill level. Only when lake level in the Lahontan basin exceeds the altitude of the highest intrabasin sill (Adrian Valley at 1308 m) does Lake Lahontan respond in an integrated manner to a change in the regional climate. SAMPLE SELECTION AND ANALYSIS Certain previously published radiocarbon-age determinations for samples of wood debris, tufa, gastropods, Chara (algal carbonate), and organic material from pack rat middens are considered reliable and have been included in this study (Tables 2 and 3). Sample locations are shown in Figure 2. New radiocarbon determinations for (1) pack rat midden organic remains from the Winnemucca Dry Lake subbasin; (2) tufa from the Smoke Creek-Black Rock Desert subbasin, the Carson Desert subbasin, the Winnemucca Dry Lake subbasin, and the Walker Lake subbasin (including Adrian Pass); (3) gastropods from the Carson Desert subbasin and the Winnemucca Dry Lake subbasin; and (4) Chara and soil from the Pyramid Lake subbasin (Astor Pass) are listed in Tables 2 and 3. Inorganic carbonates (tufa, gastropods, Chara) can be contaminated by (1) incorporation of carbon-bearing detritus, (2) precipitation of secondary carbonate cement, and (3) recrystallization of the original carbonate material. Small-scale sample contamination can be virtually impossible to detect. A few samples having radiocarbon ages <20,000 yr (Table 4) have been BENSON AND THOMPSON 72 TABLE2. Locality number (Fig. 2) RADIOCARBONAGESANDS~PLEANDLOCALITYDATAFORSELECTEDORGANICSAMPLESFROM THELAHONTAN BASIN Site name/number Laboratory number Sample type Altitude Cm) Radiocarbon age (yr B.P.) Reference Fishbone Cave No. 5 Fishbone Cave No. 3B Truckee River Delta Hidden Cave Walker Lake South Shore Fishbone Cave Truckee River Delta Hidden Cave Crypt Cave No. 2 Hidden Cave Crypt Cave No. 4 Hidden Cave Truckee River Delta Crypt Cave Guano Cave No. 1 Truckee River Delta Slope Truckee River Truckee River Delta Kramer Cave No. 1 Hidden Cave Kramer Cave GU Hidden Cave I-14059 Neotoma dung 1235 400 I-14060 Atriplex 1235 450 r 1174 670 k 55 2 3 9 L-356B I- 14065 3 3 Guano Kramer GM Hidden Hidden Cave Cave WSU-2459 WSU-2460 3 Hidden Cave WSU-2454 3 9 3 Hidden Cave Fishbone Cave Hidden Cave WSU-2458 L-364BI WSU-2452 9 9 Cowbone Cave Winnemucca Caves Fishbone Cave 9 9 14 3 16 9 14 3 9 3 9 3 14 9 9 14 14 14 13 3 13 3 9 13 9 Cave Cave WIS-363 2 100 120 1 1 WSU-2457 - Fiber bundle Rooted tree stump 1251 1212 810 i 80 980 f 40 I-14012 WIS-364 Neotoma dung Wood 1235 1173 1030 f 90 1 1110 2 55 2 WSU-2453 I-14015 Wood Atriplex and Neotoma dung Organic material Debris and Neotoma dung Burnt wood Wood 1251 1240 1880 ? 90 1910 2 80 3 1251 1240 1950 2 90 2100 * 100 3 1251 1172 2200 -' 95 2270 2 55 3 2 1240 1230 2400 2620 2 200 4 2 110 1 WIS-375 Basket Debris and Neotoma dung Wood 1166 2690 k 65 2 WIS-361 WIS-376 Wood Wood 1160 1174 2710 2890 " 60 k 50 2 2 I-14063 1288 2950 k 100 1 1251 1288 3050 3070 2 200 4 F 110 1 1251 3140 t 110 3 1230 1288 3200 3230 4 1251 1251 3520 " 120 3790 e 110 3 3 1251 3800 i 3 1251 1235 1251 3850 f 110 4150 * 150 L-289FF L-596 Debris and Neotoma dung Wood Debris and Neotoma dung Burnt organic material Wood Debris and Neotoma dung Matting Burnt organic material Charred organic material Ilrle Bag Rat dung Burnt organic debris Matting Twigs 1225 1250 5970 6500 L-289KK Net 1235 7830 2 350 WSU-2463 I-14061 WSU-2461 WIS-378 L-28911 I- 14062 L-289BB I-14064 WSU-2462 2 130 t 120 80 5365 -c 90 2 150 ? 150 1 1 1 3 4 3 4 5 4 FLUCTUATIONS TABLE Locality number (Fig. 2) 13 9 Site name/number 73 OF LAKE LAHONTAN 2-Continued Laboratory number Sample type Altitude (ml Radiocarbon age (yr B.P.) Reference L-6768 UCLA-672 Rat dung Matting 1288 1276 8300 f 200 8380 f 120 WIS-374 Wood 1168 8800 k 90 UCLA-675 Basketry 1276 9540 f 120 WIS-377 Wood 1169 9720 f 100 13 Kramer Cave Shinners Site A Truckee River Delta Slope Shinners Site A Tiuckee River Delta Slope Kramer Cave L-676A 1288 10,500 * 500 9 Fishbone Cave L-245 1235 11,200 f 250 4 15 Leonard Rockshelter Falcon Hill No. 1 Guano Cave No. 11 Falcon Hill No. 2 Crypt Cave No. P3a Guano Cave No. 7Bl Guano Cave No. 2 Guano Cave No. 6A Falcon Hill No. 2 Guano Cave No. 10 Guano Cave No. 9 Crypt Cave No. 84-2B Crypt Cave No. 1 Fishbone Cave Crypt Cave No. 84-2A c-599 Rat dung Plants Roots Bark Guano 1273 11,200 ? 570 8 I-14009 Neotoma dung 1296 11,270 2 170 1 A-3699 Juniperus cf. occident& 1230 11,580 f 290 I I-14011 Neotoma dung 1296 11,770 IT 250 1 I-14016 Artemesia 1240 11,810 -c 230 1 A-3696 Juniperus cf. occidentalis 1230 11,810 2 230 7 I-14014 Debris and Neotoma dung 1230 11,850 2 170 1 A-3695 Juniperus cf. occidentalis Juniperus cf. occidentalis Juniperus cf. occidentalis Juniperus cf. occidentalis Juniperus 1230 11,890 + 250 7 1296 12,020 f 470 7 1230 12,060 k 260 7 1230 12,070 2 210 7 1240 12,130 k 180 1 1240 12,240 ? 180 1 1235 1240 12,280 ? 520 12,350 t 180 1 1 14 9 14 13 9 13 9 9 9 9 13 9 9 9 9 9 9 A-3489 A-3698 A-3697 I-14013 and dung I-14008 Juniperus and dung AA-759 I-14010 Equus Juniperus Note. Key to references: 1 = this report, 2 = Born (1972) 3 = Davis (1985), 4 = Broecker and Orr (1958), 5 = Broecker and Kaufman (1965) 6 = Hattori (1982), 7 = Thompson et a/. (1986), 8 = Heizer (1951), 9 = M. Mifflin (Desert Research Institute, written communication, 1975). checked by uranium series dating methods (Y. Lao and L. V. Benson, unpublished data; John Rosholt, U.S. Geological Survey, written communication, 1987). With the exception of 11 porous samples of tufa (WL 4-7, WL 9- 10, WL 84: 9- 13) that were found encrusting boulders and outcrops below 1252 m in the Walker Lake subbasin, only dense forms of tufa were selected for radiocarbon analysis. The porous 74 BENSON AND THOMPSON TABLE 3. RADIOCARBON AGES ANDSAMPLEANDLOCALITYDATAFORSELECTED CHARA, AND SOIL SAMPLES FROM THE LAHONTAN BASIN Locality number (Fig. 2) Site name/ number Laboratory number Acid reduction (%I 11 11 11 11 11 11 11 11 11 11 11 11 10 3 10 11 4 7 7 5 3 1 6 2 7 6 3 7 7 7 12 12 12 7 5 2 7 2 8 5 2 8 5 2 9 6 9 2 9 8 9 5 WL 84-9 WL 84-10 WL 84-11 WL 84-12 WL 84-13 WL7 WL5 WL6 WL4 WL 10 WL9 WL 14 WL3 CD 84-8 WL2 WL 84-6 CD 85-2G PL 103 PL 102 PL 21 CD 84-7 AV 84-2 PL 113 BR 85-2 PL 104 PL 112 SM 85-4 PL 105 PL 101 PL 41G WL 102 WL 103 WL 101 PL41 PL 20 BR 85-l PL 100 BR 84-8 PL 85-2C PL 15 BR 84-5 PL 85-35: PL 18 BR 84-7 WDL 84-26 PL 110 WDL 84-3G BR 84-6 WDL 84-46 PL 85-4C WDL 84-l PL 17 USGS-4240170 USGS-4240171 USGS-4240172 USGS-4240173 USGS-4240174 I-9362 I-9360 I-9361 I-9359 I-9365 I-9364 I-9376 I-9412 USGS-4240182 I-9379 USGS-4240167 USGS-2166 I-10002 1-10001 I-9326 USGS-4240179 USGS-4240160 I-10028 USGS-2168 I-10003 I-10026 USGS-2232 I-10004 1-10000 I-9481 I-9989 I-9990 I-9988 I-9344 I-9325 USGS-2169 I-9992 USGS-4240157 USGS-2171 I-933 1 USGS-4240154 USGS-2172A I-9328 USGS-4240156 I-10019 USGS-4254144 USGS-4240155 USGS-4254143 USGS-2173 USGS-4240186 I-9329 24 22 25 29 28 55 49 50 49 52 53 50 59 24 59 24 24 40 36 55 20 32 43 30 33 36 30 43 38 10 44 40 43 56 56 30 43 24 50 55 27 100 54 22 0 42 0 22 0 50 25 55 Altitude (ml 1212 1216 1229 1235 1237 1229 1216 1222 1211 1252 1244 1318 1327 1311 1324 1306 1300 1321 1312 1325 1303 1324 1326 1332 1321 1303 1323 1324 1312 1311 1330 1330 1330 1311 1311 1306 1312 1270 1254 1230 1238 1253 1267 1254 1230.2 1256 1230.1 1245 1230 1252 1253 1260 TUFA,GASTROPOD, Radiocarbon age (yr BP.) Modern Modern Modem Modern 590 ” 60 1,205 f 75 1,335 k 75 1,720 2 80 2,185 2 80 2,970 _’ 85 4,445 f 95 12,240 k 160 12,280 f 160 12,310 -t 150 12,340 2 160 12,420 k 150 12,500 2 1000 12,540 ? 190 12,570 k 190 12,610 ? 180 12,650 k 150 12,690 -c 160 12,770 k 190 12,850 iz 600 12,850 ” 190 12,890 k 190 12,980 k 540 13,050 t 190 13,130 4 190 13,260 2 200 13,300 2 190 13,300 2 190 13,340 +- 180 13,430 2 200 13,550 -r- 200 13,810 I 600 13,820 t 200 14,090 * 190 14,090 ? 1600 15,140 2 250 15,510 ? 170 15,660 ” 150 16,510 f 250 16,900 k 270 17,170 2 270 17,300 k 200 17,800 2 640 18,030 2 470 18,030 5 300 18,130 + 800 18,260 * 230 18.580 f 310 Reference 1 1 1 1 1 2 2 2 2 2 2 2 2 1 2 1 1 2 2 2 1 1 2 1 2 2 1 2 2 2 2 2 2 2 2 1 2 1 1 2 1 1 2 1 1 2 1 1 1 1 1 2 FLUCTUATIONS TABLE Locality number (Fig. 2) 8 2 5 5 6 6 Site name/ number PL BR PL PL PL PL 85-W 84-4 23 22G 109 108 Laboratory number OF LAKE LAHONTAN 75 3-Continued Acid reduction (%I USGS-2174 USGS-4240153 I-9342 I-9482 I-999 1 I-10018 50 32 49 10 46 42 Altitude Cm) 1251 1231 1260 1260 1242 1235 Radiocarbon age (yr BP) 18,970 19,520 19,530 19,620 19,820 19,990 f 2 ” k e + 1000 380 350 360 340 380 Reference 1 1 2 2 2 2 Note. Key to references: 1 = this report, 2 = Benson (1981). samples may have accumulated carbon during more than one minor lake cycle during the Holocene; therefore, the apparent radiocarbon ages are considered provisional. After the visibly weathered surface of each tufa sample was removed, a thin section was made of each sample. The thin section was examined petrographitally; if secondary material or evidence of recrystallization was found, the sample was rejected. Tufa samples, as well as gastropod and Chara samples, were acidleached prior to radiocarbon analysis to remove any surticial contaminant (Table 3). Organic samples from middens were also treated with acid to remove possible carbonate contaminants (Thompson et al., 1986). LAKE-LEVEL RESULTS Uranium series and radiocarbon ages of organic and inorganic materials listed in Tables 2 and 3 are plotted in Figures 3-5 as a function of altitude for Pyramid Lake, Winnemucca Dry Lake, Smoke CreekBlack Rock Desert, Carson Desert, and Walker Lake subbasins. A model chronology of lake-level variation based solely on data from the western Lahontan subbasin is shown in each graph as a solid line. The western Lahontan data set was used to formulate the model lake-level chronology because of the large number and variety of samples from that region. The tigures are ordered in such a way as to represent surface-water communication between the lake in the Pyramid Lake subbasin and lakes in other subbasins as a function of sill altitude (Fig. 1; Table 1). This ordering does not imply sequence of basin filling, but rather poses certain limits on times when lake levels within connecting basins could have been the same. For example, if, in the past, the level of Pyramid Lake was at an altitude of 1250 m, then connecting lakes could have existed in the Smoke Creek-Black Rock Desert, Honey Lake, and Winnemucca Dry Lake subbasins (Figs. 1 and 3). Therefore, material deposited in those lakes at that time would not be found at altitudes exceeding 1250 m. DISCUSSION Central Basin Lake Chronology 100 yr B.P. 45,000 to Radiocarbon dates of surficial materials from five Lahontan subbasins (Figs. 3-5) indicate consistent lake-level histories. Of particular interest is the rate of change of lake level with respect to time. The age of the earliest indication of a lake is about 45,000 yr B.P. in the Smoke Creek-Black Rock Desert subbasin. At that time, a moderate-sized lake connected the Smoke Creek-Black Rock Desert, Honey Lake, Pyramid Lake, and Winnemucca Dry Lake subbasins (Figs. 1 and 3). By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m, where it remained for 3500 yr. Davis (1983) corre- 76 BENSON AND THOMPSON 42 EXPLANATION - OUTLINE LAKE 38 01 1 , I tp0 50 MILES SAMPLE OF LAHONTAN LOCALITY r(lLOMETERS FIG. 2. Localities of dated samples in the Lahontan basin. lated a tephra that crops out at 1251 m in the Black Rock Desert with the 23,400-yr B.P. Trego Hot Springs tephra. This datum was used in constructing the model lakelevel chronology. The sill (Darwin Pass) that connects the western Lahontan subbasins with the Carson Desert subbasin also has an altitude of 1265 m; this implies that lake levels in the western subbasins were stabilized by spill from the Pyramid Lake subbasin to the Carson Desert subbasin until 16,500 yr B.P. (Fig. 3). By 16,000 yr B.P., lake level in the western Lahontan subbasins had fallen to 1240 m. The timing of this recession is based on a date of 15,660 ? 150 yr B.P. BR 84-2 BR 84-l BR 84-3 WLl WL 84-2 WL 84-7a WL 84-8 WL 84-5 WL 84-l WL 84-3a WL 84-4 WL 84-3d PL 14 2 2 2 l-9339 USGS-4240165 USGS-4240164 USGS-4240163 USGS-4240168 USGS-4240169 USGS-4240166 USGS-4240161 I-9378 USGS-4240162 USGS-4240151 USGS-4240150 USGS-4240152 Laboratory number 1219 1214 1219 1312 1266 1315 1317 1302 1260 1270 1271 1270 1209 21 21 31 21 20 51 Altitude Cm) 26 26 41 21 26 24 23 Acid reduction (%) 420 450 1 450 750 910 600 I 1380 1030 1120 2600 2310 2860 Radiocarbon age (yr BP.) 22,140 2 23,300 + 23,300 * 25,280 2 28,720 f 28,720 k 31,840 + 29,630 * 30,300 2 32,210 +33,220 f 36,990 + >40,000 Note. Key to references: 1 = this report, 2 = Benson (1981), 3 = Lao and Benson (1987). a Composite analysis done by Yong Lao at Columbia University. * Analysis by John Rosholt of the U.S. Geological Survey. 5 IO 11 11 11 11 11 11 11 11 Site name/ number 35,000 - 49,000 - 29,000 - ?I 10,000* ‘- 3oooe - k 4m Z3oTh/z”U age (yr B.P.) 4. RADIOCARBONAGESANDSAMPLEANDLOCALITYDATAFORSELECTED TUFASAMPLESHAVINGAGESOF>~O,OOOYRB.P. LAHONTAN BASIN Locality number (Fig. 2) TABLE 12 1 1 1 1 1 1,3 173 1 2 192 12 172 Reference FROMTHE BENSON AND THOMPSON 78 1320 Adrian - Pass _ 1280 - 1270 - Darwin _--- Pass 131OL - Walker --AC---__-_ Lake subbasm connected 1300- z Carson d-M--_-- g 1260- 7 E 1250- connected - indvzates lake level 0 00 l wo12302 OI 1220- m 3 1210w Emerson 5 subbasm Dashed line approximate 0 <1240- Desert . ! Smoke Creek/ -------- Pass ---i- 1200- 2 i i llso- Wlnnemuca .I 11~0 - Mud Lake Slough ,.’ 1160- Lake subbasm bottom - o . T = 1054m - 1150,,&--L---I A-. 5 0 1. 15 lo subbasm connected EXPIANATION 1170 -vyz.T-;0 0 Pyramid Dry Lake -f -e;6,_m--.mL_2TIME (103yr Materials formed below lake level Materials formed above lake level Tephra layer Lake Lahontan model chronology Sill altitude 1 - 25 30 35 40 45 BP) FIG. 3. Model lake-level chronology derived using data from the Pyramid Lake, Winnemucca Dry Lake. and Smoke Creek-Black Rock Desert subbasins. g 1280 +k 1270 _I Darwin i Pass 2 1260w g 1250- 1 l -- :: 1240 ? 1230- :5 1220 - 1210 - 1200 -Carson subbasin 1190. 1170- 0 ’ Desert bottom 5 EXPLANATION 0 . Maferlals formed below Lee iwe, Malerlafs tonned abwe lake level Lake Lahootan model phrenology - - Sill allltude 10 TIME (10syr 15 B.P.) 20 25 FIG. 4. Model lake-level chronology compared with data from the Carson Desert subbasin. obtained from the organic component of a soil (sample PL 853S, Table 3) sandwiched between two Chara deposits. The upper Chara deposit (PL 852C, Table 3) is dated 14,090 + 1600 yr BP, and the lower Chara deposit (PL 854C, 5C, Table 3) is dated 18,130 + 800 and 18,970 f 1000 yr BP This recession apparently was synchronous with a desiccation of Walker Lake (see below). From about 15,000 to 13,500 yr BP., lake level rose rapidly, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand of 1330 m by 13,500 yr B .P., a condition that persisted until -12,500 yr B.P. At 12,500 yr BP, lake level fell h 100 m during a time interval so short (~500 yr) that the magnitude of the counting error associated with radiocarbon analysis precludes a more precise determination of the length of the interval. FLUCTUATIONS :i[ Adrian P&s fl OF LAKE Walker _ 79 LAHONTAN Lake subbasin connected “-series date 1300 E 1290 t iii 1280- c’ F < w 12701260- 0 Materials formed below lake level 0 - Deslccallon Walker Lake - - Sdl altdude - -?1170 ’ 0 5 r-r- - 10 15 20 TIME~:03yr B.i$ -I- -?35 -?- -? 40 FIG. 5. Model lake-level chronology compared with data from the Walker Lake subbasin. No data exist that indicate the altitude of lakes in the various subbasins between 12,000 and 10,000 yr B.P. Radiocarbon dates of nonlithoid tufa in this age range (Broecker and Orr, 1958; Broecker and Kaufman, 1965; Benson, 1978; Benson, 1981) have been demonstrated to be in error (Thompson et al., 1986). In the absence of data, we cannot with certainty assess whether an extreme lowstand (such as that which occurred in the Bonneville basin; Currey and Oviatt, 1985) followed the last highstand. In the Pyramid Lake subbasin, Born (1972) recovered wood samples dated at 9720 ? 100 and 8800 + 90 yr B.P. from altitudes of 1169 and 1168 m, respectively, from the ancestral Truckee River delta. Born interpreted these data as indicating that Pyramid Lake was at an altitude > 1168 m from 9700 to 8880 yr B.P. Prior to irrigation, the surface altitude of Pyramid Lake was in the range of 1177 to 1180 m (Born, 1972); thus, Born’s data imply that during a part of the early Holocene* the altitude of Pyramid Lake was not substantially lower than the historic level. Tufas of mid-Holocene age have not been found in any of the central Lahontan subbasins. Hubbs et al. (1963, 1965) and Harding (1965) discovered the remains of 4500-yr-old tree stumps 60 cm below the modern level of Lake Tahoe. Davis et al. (1976) believe this indicates that in the middle Holocene, Lake Tahoe fell below the level of the sill that governs spill of this lake into the Truckee River. Loss of this source, which supplies 30% of the discharge to the Pyramid Lake and Winnemucca Dry Lake subbasins, certainly would have resulted in a lowering of lakes in those subbasins. ’ For the purposes of this paper, early, middle, and late Holocene periods are arbitrarily defined as 10,000 to 7000, 7000 to 4000, and 4000 yr B.P. to present, respectively. 80 BENSON AND Harding (1965) offered an alternative hypothesis to explain the presence of submerged trees in Lake Tahoe. He suggested that tectonic movements may have affected the relative altitude of Lake Tahoe’s strandline and lowered the ground on which the trees grew during the past 5000 yr. We believe that existing evidence argues against a period of extreme aridity during the mid-Holocene and that Harding’s (1965) hypothesis is correct. Persistence of endemic fish (cui-ui and emerald trout) in Pyramid Lake until the end of the late Holocene indicates that the lake has not decreased in size to the point that the fish could not survive (Snyder, 1918). Since 1892, Pyramid Lake has fallen about 22 m, passing through a minimum level of 11.53 m in 1967, which is 24 m lower than the 1844 level of 1177 m. The emerald trout did not survive this artificial lowering of lake level, and the cui-ui had to be raised in fish hatcheries external to the lake; these facts indicate that Pyramid Lake did not fall much below its historic preagricultural lowstand of 1177 m (Harding, 1965) during the midHolocene. This evidence further implies that Lake Tahoe did not fall below sill level for any significant time in response to a mid-Holocene period of aridity. A salt-balance calculation using chloride also indicates that Pyramid Lake probably has not desiccated since the last highstand. The following argument assumes that chloride precipitates, once formed, would not have had sufficient time to redissolve and completely diffuse into the overlying lake water. The total amount of chloride stored in the Pyramid Lake and Winnemucca Dry Lake subbasins is equal to the mass of chloride dissolved in lake water plus the mass of chloride dissolved in pore fluids beneath the sediment-water interface. Winnemucca Lake contained 0.26 x lOlo kg of chloride in 1924, and Pyramid Lake contained 5.36 x lOlo kg of chloride in 1976 (Clarke, 1924; Benson, 1984). After THOMPSON correcting for diversion, the mean annual volume of water discharging to Pyramid and Winnemucca Dry Lakes is estimated to range from 0.75 to 1.00 km3 yr-‘. The smaller discharge limit represents the mean annual discharge of the Truckee River measured at Farad, California (site 346000; Fig, 6) for 1900-1983 (U.S. Geological Survey, 1960, 1963, 1961-1984). The larger discharge limit was calculated assuming that Pyramid and Winnemucca Lakes had surface areas corresponding to historic lakesurface altitudes of 1175 m and evaporation rates of 1.25 m yr-l. Instantaneous values of discharge and chloride concentration, available on a monthly basis for 1968-1980 (Desert Research Institute, University of NevadaReno database), were used to calculate a discharge-weighted mass-flow rate of chloride. The mass-flow rate (2.13 x lo6 kg yr-l) was divided into the total chloride mass dissolved in Pyramid Lake and Winnemucca Lake water. The calculation indicates that it would have taken 26,000 yr for the Truckee River to supply the amount of chloride presently dissolved in these lakes. Accounting for the amount of chloride dissolved in pore fluids of Pyramid Lake sediments that were deposited since the last highstand increases the calculated flow period by about 10%. Using the larger discharge bound of 1.00 km3 yr-i decreases the flow period by 533%. The part of the calculated flow period in excess of 12,500 yr is meaningless because the mass of chloride in excess of that contributed by the Truckee River during the last 12,500 yr was inherited from Lake Lahontan. In any case, the calculation indicates that Pyramid Lake did not desiccate during the last 12,500 yr, contrary to the results of earlier calculations (Russell, 1885; Jones, 1925). In the Pyramid Lake subbasin, Born (1972) discovered late-Holocene lacustrine sediments above an angular unconformity marking an earlier lowstand of unknown altitude. Radiocarbon dates on these lake deposits indicate that a rise in lake level to FLUCTUATIONS OF LAKE 81 LAHONTAN OREGON 42’ .- I .- EXPLANATION ImJCKKE NVER \ Exixtlng laker A360800 Aotlvo flow with latod numbor I_ 4QERLACH Active ltatlon colloctlon 8yatom xtatlon ,_ WE y . ,L ,, 0 / , ( 1yo 2 1167 m began prior to 2700 yr B.P. From other field evidence, Born suggested that the rise began as early as 3500 yr B.P. Chronology Walker Lake is the most southerly subbasin of the Lahontan system; it is joined to the central body of Lake Lahontan only when the latter is at its highest levels 1 abbrovl tatlon preclp with nom0 DAHO P KILOMETERS @ SO MILES 1 FIG. 6. Locations of selected streamflow-gauging Walker Subbasin Lake-Level 50,000 to 100 yr B.P. ,_ stream rtatlon I 1 and weather stations in the Lahontan basin. (>1308 m). Since the initial studies of Russell (1885), it has been postulated that the history of Walker Lake may have been affected by diversion of the Walker River into the Carson River through Adrian Valley (King, 1978; Davis, 1982). King (1978) claims to have found geomorphic evidence for diversion of the Walker River through Adrian Valley. However, the sedimentological record left by 82 BENSON AND the hypothetical diversion remains undated, and it also could have occurred as the result of Walker Lake spilling into the Carson drainage 14,000 yr ago. Ongoing uranium series studies of tufa in the Walker subbasin (Y. Lao and L. V. Benson, unpublished data) indicate that Walker Lake was full and spilling to the Carson Desert subbasin about 49,000 yr B.P. (Fig. 5). On the basis of chemistry of pore fluids extracted from Walker Lake sediment cores, Benson (1978) deduced that the lake had desiccated in the past. Subsequent studies of the geochemistry and the porosity distribution of other cores taken in 1984 (L. V. Benson, unpublished report) indicate that Walker Lake was dry three times during the past 40,000 yr. The first desiccation occurred between about 40,000 and 15,000 yr B.P. The second desiccation commenced sometime after 12,500 yr B.P. and ended about 4700 yr B.P. The last desiccation occurred between about 2800 and 2000 yr B .P. After 2000 yr B .P., the lake rose again. Radiocarbon dates of Holocene tufas from the Walker Lake subbasin (Fig. 5) are in approximate agreement with this proposed chronology. Given that Pyramid Lake probably has not desiccated during the past 45,000 yr, and that the annual discharge of the Walker River and Truckee River are highly correlated (R* = 0.9), we believe that the last three Walker Lake desiccations probably occurred as the result of diversion of the Walker River. CLIMATIC AND HYDROLOGIC IMPLICATIONS OF LAKE-LEVEL CHANGE Lake-Level Change: 15,000 to 12,000 yr B.P. The lake-level chronology depicted in Figure 3 is characterized by a rise of lake level between 15,000 and 13,500 yr B.P. to the 1330-m highstand and a fall of lake level from the 1330-m highstand to about 1180 m THOMPSON between 12,500 and 12,000 yr BP. These relatively rapid changes in lake level were associated with large changes in the surface areas of lakes in the Lahontan basin; e.g., the fall in lake level was associated with a 93% reduction of surface area. What type of changes in the hydrologic balance could have led to the rapid change in lake level 15,000 to 12,000 yr B.P.? To answer this question, simulations of the dynamics of lake-level change were attempted. Simulations of the Dynamics Lake-Level Change of To simulate the rate of lake-level change that occurred between extreme lake-level states, it was assumed that change from one hydrologic state to another occurred in a discontinuous step-like manner. Two simulations of the rate of lake-level change were made, using a computer program (FILLSPIL) developed by Frederick Paillet of the U.S. Geological Survey. Input to FILLSPIL consists of values for river discharge, lake-surface precipitation, lake evaporation, and lake depth for each of the Lahontan subbasins. FILLSPIL uses the bathymetry and topography of the Lahontan subbasins given in Benson and Mifflin (1986). The output for FILLSPIL consists of changes in lake-surface altitude, lake depth, and lake area as a function of time. The first simulation was designed to determine how long it takes Lake Lahontan to go from a completely dry state to a 1330m highstand. Depth of water in all Lahontan subbasins was set to zero, and the hydrologic balance was adjusted to correspond to a state that eventually would reach the 1330-m highstand-equilibrium state. Results of the simulation indicated that the highstand-equilibrium state could be achieved in ~100 yr. The second simulation was designed to determine how long it takes Lake Lahontan to fall from the 1330-m highstand to the 1180-m level in the Pyramid Lake subbasin. FLUCTUATIONS OF LAKE Depths of water in all subbasins were set to their highstand values and the hydrologic balance was adjusted to correspond to a state that eventually would reach equilibrium with the 1180-m state. Results of this simulation indicated that it takes ~250 yr for Lake Lahontan to fall from 1330 to 1180 m. It has been shown that the observed dynamics of lake-level change in the Lahontan basin can be simulated, if it is assumed that the hydrologic balance switches rapidly from one equilibrium state to another. What climatic mechanism or process led to such large and rapid changes in the hydrologic balance of the Lake Lahontan system? The Relation of Climate and the Hydrologic Balance of the Lahontan Basin The record of lake-level variation in the Lahontan basin is considered to result from climatic change. On a global scale, climatic variations in the Lahontan area are caused by changes in the strength of the circumpolar vortex and the wavelength and amplitude of long (Rossby) waves in the midlatitude westerlies. The pattern of these waves determines the development, movement, and intensity of synoptic-scale features of circulation, such as cyclones, anticyclones, fronts, and jet streams. Synoptic-scale circulation at any given location is modified by topography and other characteristics of the regional and local setting. About 40 yr ago, Antevs (1948, p. 170) suggested that: When the west-Canadian ice sheets were large . . modem summer conditions could not establish themselves, though, of course, the temperature rose especially outside the ice sheets causing seasons, but the . . . winter conditions of pressure and precipitation were fairly permanent. The Aleutian Low persisted through the summer, and the subtropical high pressure may have remained on or below Lat. 30” As a consequence moving cyclones, bringing precipitation, crossed the western United States in spring, LAHONTAN 83 summer, and autumn as well as in winter. Hence the West had a pluvial period. Since 1948, several authors (Riehl et al., 1954; Horn and Bryson, 1960; Sabbagh and Bryson, 1962; Pyke, 1972) have suggested that the progression of maximum precipitation along the western coast of North America is associated with the southward movement of the mean position of the jet stream. Recently, Kutzbach and Wright (1985) performed several climate-simulation experiments, using the Community Climate Model (CCM) of the National Center for Atmospheric Research (NCAR). Model results for 18,000 yr B.P. indicate that the jet stream splits around the North American ice sheet and that the southern branch strengthens considerably over the southwestern part of the United States. Thus, synoptic-scale observations and CCM experiments appear to confirm Antevs’ (1948) suggestion that the rise and fall of Great Basin lakes is associated with the mean position of the jet stream and that the presence of a large continental ice sheet tends to force the jet stream over the southwestern United States. In light of these observations, we suggest that the record of lake-level change in the Lahontan basin is principally a record of the changing mean position of the jet stream. The 1330-m highstand that occurred 14,000 to 12,500 yr B.P. is considered to have resulted from the repositioning of the jet stream within the latitude range 39” to 42”N. The shape of the lakelevel record indicates that change in the position of the jet stream, and therefore, change in the climate of an area, takes place rapidly. Since the jet stream moves in response to changes in ice-sheet height and size (Kutzbath and Wright, 1985), and since the icesheet record is forced astronomically (Peltier and Hyde, 1984), we suggest that Great Basin lake and groundwater recharge cycles likely are related to the continental ice-sheet record, or its proxy, the ?Y*O BENSON AND THOMPSON 84 record in deep-sea cores (e.g., Imbrie et al., 1984). Therefore, major lake cycles likely will occur at about lOO,OOO-yr intervals. This subject will be treated in more detail in a forthcoming publication. SUMMARY AND CONCLUSIONS A model chronology has been presented of fluctuations of Lake Lahontan for the past 50,000 yr. A moderate-size lake probably connected three western Lahontan subbasins (the Smoke Creek-Black Rock Desert subbasin, Pyramid Lake subbasin, and Winnemucca Dry Lake subbasin) from 45,000 to 16,500 yr B.P. Between 50,000 and 45,000 yr B.P., Walker Lake rose to its sill level and spilled to the Carson Desert subbasin. By 20,000 yr B.P., lake level in the western Lahontan subbasins had risen to about 1265 m, where it remained for 3500 yr. By 16,000 yr B.P., lake level in all western Lahontan subbasins had fallen to 1240 m. From about 15,000 to 13,500 yr B.P., lake level rose rapidly, so that Lake Lahontan was a single body of water by 14,000 yr B.P. The lake appears to have reached a maximum highstand altitude of 1330 m by 13,500 yr BP., a condition that persisted until about 12,500 yr B.P., at which time lake level fell 2100 m. No data exist that indicate the level of lakes in the various subbasins between 12,000 and 10,000 yr B.P. Walker Lake was dry from about 40,000 to about 15,000 yr B.P., probably as a result of the diversion of the Walker River to the Carson Desert subbasin. The Holocene was characterized by low lake levels, with many subbasins being the site of one or more periods of desiccation. A salt-balance calculation, as well as the persistence of endemic fish in Pyramid Lake, indicate that Pyramid Lake probably did not desiccate since the last highstand. The shape of the lake-level curve for the three western subbasins indicates that past changes in the hydrologic balance (and hence climate) were large in magnitude and took place in a rapid step-like manner. The rapid changes in lake level are hypothesized to have resulted from changes in the mean position of the jet stream, as it was forced north or south by the changing size and shape of the continental ice sheet. ACKNOWLEDGMENTS Funding for this research was provided by the National Research Program of the U.S. Geological Survey. The authors thank William Scott, Harold Weaver, and Briant Kimball of the U.S. Geological Survey for their useful suggestions. The authors also acknowledge the assistance of Cecil Rousseau and Pamela Feldhauser in preparing the manuscript. REFERENCES Antevs, E. (1948). The Great Basin, with emphasis on glacial and post-glacial times-Climatic changes and pre-white man, Chap. III. Bulletin of the University of Utah Biological Series 38, 168 191. Benson, L. V. (1978). Fluctuation in the level of pluvial Lake Lahontan during the last 40,000 years. Quaternary Research 9, 300-318. Benson, L. V. (1981). Paleoclimatic significance of lake-level fluctuations in the Lahontan Basin. Quaternary Research 16, 390-403. Benson, L. V. (1984).“ Hydrochemical Data for the Truckee River Drainage System, California and Nevada.” U.S. Geological Survey Open-File Report 84-440. Benson, L. V. (1986). “The Sensitivity of Evaporation Rate to Climate Change-Results of an Energy-Balance Approach.” U.S. Geological Survey WaterResources Investigations Report 86-4148. Benson, L. V., and Mifflin, M. D. (1986). “Reconnaissance Bathymetry of Basins Occupied by Pleistocene Lake Lahontan.” U.S. Geological Survey Water Resources Investigations Report 85-4262. Born, S. M. (1972). “Late Quatemary History, Deltaic Sedimentation, and Medlump Formation at Pyramid Lake, Nevada.” Center for Water Resources Research, Desert Research Institute, University of Nevada System unnumbered publication. Broecker, W. S., and Kaufman, A. (1965). Radiocarbon chronology of Lake Lahontan and Lake Bonneville. II. Great Basin. Geological Society of America Bulletin 16, 537-566. Broecker, W. S., and Or-r, P. C. (1958). Radiocarbon chronology of Lake Lahontan and Lake Bonneville. Geological Society of America Bulletin 69, 1009- 1032. Broecker, W. S., and Walton, A. (1959). 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A revised chronology for the last Pleistocene lake cycle in the central Lahontan Basin. Quaternary Research 25, l-9. U.S. Geological Survey (1960). “Compilation of Records of Surface Water of the United States Through September 1950,” Part 10, “The Great Basin.” U.S. Geological Survey Water-Supply Paper 1314. U.S. Geological Survey (1963). “Compilation of Records of Surface Water of the United States, October 1950 to September 1960,” Part 10, “The Great Basin.” U.S. Geological Survey Water-Supply Paper 1734. U.S. Geological Survey (1961-1984). “Water Resources Data for Nevada (1961-1984)” U.S. Geological Survey Water-Data Report Series.
