In the Pleistocene, Idaho was a cooler, wetter place. Trees grew on the Snake River plain during maximum glacial cool intervals about 140,000 and 20,000 years ago. When the glaciers melted, constrictions in canyons produced local dams and periodic floods, on the Snake River, Columbia River, and Big Lost River systems.
In many cultures around the world there are flood legends. Floods occurred in many different places as the Pleistocene glaciers melted and sea level rose. As water formerly stored in ice melted to raise sea level, extensive coastal flooding occurred. Such flooding in the Caspian Sea may be the origin of the story of Noah's flood in the Old Testament.
This map of glacial geology in Idaho is linked to a larger PDF file.
Figure 1 shows areas of Idaho affected by latest Pleistocene glaciation and the Bonneville, Missoula and Big Lost River Floods (slightly modified from Cerling and others, 1994). Glaciation was present both north of the Snake River Plain (in the Pioneer, Lost River, Lemhi, and Beaverhead Ranges, plus the Sawtooth, Salmon River and Bitterroot Ranges) and in the Albion Range south of the Plain. (Figure from Link and Phoenix, 1996, Rocks, Rails and Trails.
Figure 1. Map of Idaho with Pleistocene glaciation and Bonneville, Missoula and Big Lost River Floods (Figure from Link and Phoenix, 1996, Rocks, Rails and Trails (http://imnh.isu.edu/digitalatlas/geog/rrt/part2/24.htm#2).
Extent of Glaciation
Figure 2 shows the extent of glacial ice in North America in the Late Wisconsin about 20,000 years ago. The Laurentide continental ice sheet on the east and the Cordilleran ice sheet on the west are divided by the Rocky Mountains. Idaho was influenced by both climatic effects of the Rocky Mountains and Yellowstone area on the east and the wetter Pacific Northwest climate on the north and west. In northern Utah the growth of Lake Bonneville served to make the climate there more moist, and to provoke "lake effect" snows, which focused precipitation in the Wasatch and Uinta Mountains. This expanded the impact of the glaciers, and ultimately provided a positive feedback for growth of Lake Bonneville. On this map the Sawtooth Mountains represent the middle small patch of ice in the northern Rocky Mountains.
Figure 2. Late Wisconsin extent of glacial ice in North America. The Sawtooth Mountains represent the middle small patch of ice in the northern Rocky Mountains (Thackray et al., 2004, and Sherard, 2006).
Figure 3. Location of Sawtooth Mountains in central Idaho --Sawtooth Mountains, IdahoThackray et al., 2004, and Sherard, 2006.
Chronology of Glaciation
The record of oxygen isotopes in marine successions tracks the overall general temperature of the ocean water, and thus, ultimately the glacial history. In general, the climate was coldest about 140 ka (the Illinoian (Bull Lake) glaciations), warmed to present levels by 120 ka, and then cyclically cooled to 20 ka (the Wisconsin (Pinedale) glaciations), after which a major warming, Holocene deglaciation, and rise in sea level occurred (the present) (figure 4).
- At Oxygen Isotope Stage 4/5 (about 60 ka) was the maximum advance in Olympics and Cascade mountains
- At ca. 33 ka there was a major advance in the Olympics (and Sawtooths?)
- At ca. 19-22 ka (Last Glacial Maximum) there was the maximum Late Pleistocene advance in Wallowa Mountains of eastern Oregon, and in the Sawtooths, with lesser advances in the Olympics and Cascades
- At ca. 17 ka was the maximum advance of the Puget Lobe of the Columbian Ice Sheet, plus a readvance or recessional still stand in the Wallowa Mountains and in the Sawtooths
- At ca. 14 ka there was a readvance or recessional still stand in Sawtooths
- At ca. 11-12 ka there was a readvance or recessional stillstand in the Wallowas and the Sawtooths
Figure 4 . Summary of Northwestern US Glacial Advances (from G.D. Thackray, Idaho State University). This figure shows the timing of glacial advances in the western U.S. The point is that on the fine scale of time, glacial advances did not happen at the same time in different climatic zones, even in the northwestern U.S.
The marine oxygen isotope stages 2-4, and possibly stage 5d, represent the
Wisconsin glaciation ]or Pinedale], while stage 6 represents the Illinoian
glaciation [or Bull Lake] (Figure 4). The last glacial maximum (from 18,000
to 14,000 14C yr BP) is represented by the peak in oxygen isotope
stage 2. Latter stage 2 to stage 1 (ca 14,500 14C yr BP to 10,000
14C yr BP) is loosely termed late-glacial (from Borgert, 1999;
Figure 5. Composite of oxygen isotope records of benthic foraminifera from several deep sea cores reflecting global ice volume (Shackleton and Pisias, 1985; Martinson et al., 1987; Porter, 1989).
In the McCall to Cascade area of Long Valley, a recent Idaho Geological Survey surficial geologic map by Breckenridge and Othberg, 2005, is available from the Idaho Geological Survey - Surficial Geologic Map of the McCall area, Valley and County, Idaho: Idaho Geological Survey Digital Web Map DWM-35.
The chronology of Middle and Late Pleistocene glaciations in the Rocky Mountains have local names. In general, we can think of a Middle Wisconsin, ~140ka Bull Lake (Copper Basin) advance, and one or more Wisconsin (~70 to 20 ka) Pinedale (Potholes) advances.
Figure 6. Previous work conducted on glacial sequences in central Idaho, summarized by Borgert (1999).
Figure 7. Map of late Pinedale moraines from Pettit to Hell Roaring Lake, Sawtooth Mountains, from Borgert, 1999.
Figure 8. LIDAR image of moraines in the Stanley Basin.
Redfish Lake is the upper box and Alturas Lake is the lower box. From G.D.
Thackray, Idaho State University.
Figure 9. Chronology of glaciations at Alturas Lake, Sawtooth Mountains.
Figure 10. Note several late Pinedale moraines.
Glaciers have affected most of the high mountains of Idaho. The slide show for this module, by Jim Cash of the Idaho Geological Survey, shows glaciated terrane in the Lost River Range and Pioneer Mountains.
The above photos are by Paul K. Link, Idaho State University, all in the Sawtooth Mountains, Idaho.
Cerling, T.E., Poreda, R.J., and Rathburn, S.L., 1994, Cosmogenic 3He and 21Ne age of the Big Lost River flood, Snake River Plain, Idaho: Geology, v. 22, p. 227-230.
Gosse, J.C., Evenson, E.B., Klein, J., Lawn, B., and Middleton, R., 1995, Precise cosmogenic 10Be measurements in western North America : Support for a global Younger Dryas cooling event: Geology, v. 23, p. 877-880.
Licciardi, J.M., Clark, P.U., Brook, E.J., Pierce, K.L., Kurz, M.D., Elmore, D., and Sharma, P., 2001, Cosmogenic 3He and 10Be chronologies of the late Pinedale northern Yellowstone ice cap, Montana, USA: Geology, v. 29, p. 1095-1098.
Licciardi, J.M., Clark , P.U., Brook, E.J., Elmore, D., and Sharma, P., 2004, Variable responses of western U.S. glaciers during the last deglaciation: Geology, v. 32, p. 81-84.
Sherard, C., 2006, Timing of early Holocene Glacial Advances in Idaho and Washington. Unpublished M.S. Thesis, University of Washington.
Thackray, G.D., 2001, Extensive early and middle Wisconsin glaciation on the western Olympic Peninsula, Washington, and the variability of Pacific moisture delivery to the Pacific Northwest: Quaternary Research, v. 55, p. 257-270.
Thackray, G.D., Lundeen, K.A., and Borgert, J.A., 2004, Latest Pleistocene alpine glacier advances in the Sawtooth Mountains, Idaho, USA: Reflections of midlatitude moisture transport at the close of the last glaciation: Geology, v. 32; no. 3; p. 225-228; doi: 10.1130/G20174.1