1. Pluvial Lakes Latin word for rain is “pluvia.”
Pluvial lakes represent large paleolake systems that formed in semi-arid to arid environments throughout Quaternary.
Pluvial lakes record periods of either higher precipitation and/or lower evaporation rates.
The timing of pluvial lake formation occurs in either glacial or interglacial periods, depending upon atmospheric and oceanic circulation patterns.
The pluvial lakes within the Great Basin region had their highest lake levels during glacial periods.

2. Bonneville Provo Stansbury Gilbert The Mass Balance of Pluvial Lakes
The change in lake volume = input - output of water into the lake basin.
V = I - O
The change in surface area of the lake (and lake level) depends upon the V and basin topography.
Bonneville
Provo
Unnamed shoreline
Stansbury
Six shorelines of glacial Lake Bonneville are identified in the image on the left. The shorelines represent different high stands and were incised by wave erosion when the lake level stabilized.
Gilbert
Unnamed shoreline
Shorelines of Lake Bonneville on Antelope Island
Well-defined shorelines are visible at Buffalo Point on the northwest side of Antelope Island. Notice that there are more than four shorelines present. Dozens of unnamed shorelines associated with the oscillations of Lake Bonneville can be seen around the Bonneville basin.

3. Mass Balance of Lake Water
I = precipitation on lake, surface runoff from surrounding drainage basin, groundwater inflow.
O = evaporation, surface outflow, and ground water outflow.
Controls on Water Input (I)
Preciptiation rate
Temperature (effect on evaporation from the lake surface and to a lesser extent, wind)
Controls on Water Output (O)
Elevation of the lake surface relative to the outflow point (sill).
Lake area (greater surface area, greater evaporation.
Temperature (higher temperature, greater evaporation.
Other factors (groundwater outflow rate, wind).
Great Basin Pluvial Lakes

4. Pluvial Lakes of the Great Basin
Formed during glacial periods and persisted into the glacial-interglacial transition.
Largest Lakes
Lake Bonneville (northwestern Utah).
Lake Lahontan (western Nevada) .

5. The Rise and Fall of Lake Bonneville
Provo Level
17,000 years ago
Great Salt
Lake today
Bonneville Level
18,000 years ago
Gilbert Level
12,000 years ago
The Rise and Fall of Lake Bonneville
The hydrograph for Lake Bonneville represents lake levels over the past 24,000 years. Maps of Lake Bonneville (background) indicate when the four major shorelines were formed; Stansbury, Bonneville, Provo and Gilbert. The location of present-day Great Salt Lake is depicted in dark blue.
Hydrograph of Lake Bonneville
Stansbury Level
24,000 years ago

6. Stansbury Shoreline ~ 24,000 years ago
Ogden
Delta
Nephi
Provo
Salt Lake UT ID NV
Red Rock Pass
Stansbury Shoreline
~24,000 years ago
Climate was cooler and wetter. Lake began to rise from a level close to present-day Great Salt Lake.
Stansbury Island
Stansbury Shoreline ~ 24,000 years ago
This map shows the Stansbury level of Lake Bonneville about 24,000 years ago. At this time, cooler and wetter climate conditions caused the lake to begin to rise from a level close to that of the present-day Great Salt Lake. The Stansbury shoreline, the oldest of the four major shorelines, actually formed during the transgressive phase of Lake Bonneville as the lake was rising. The Stansbury shoreline is usually difficult to see, but can be spotted (from I-80) on the south end of Stansbury Island.

7. Bonneville Shoreline ~18,000 years ago
Red Rock Pass UT ID NV
Bonneville Shoreline
~18,000 years ago
Lake level controlled
by spillway near Red
Rock Pass, Idaho.
Ogden
Delta
Nephi
Provo
Salt Lake
Point of the Mountain
Bonneville Shoreline ~18,000 years ago
This map depicts Lake Bonneville about 18,000 years ago. This is the highest stage of Lake Bonneville and at this time the lake level was controlled by a threshold near Red Rock Pass, Idaho. About 17,500 years ago, the threshold broke and water spilled out catastrophically into the Snake River drainage. This event is called the Bonneville flood. It is estimated that in less than one year, the amount of water that flowed out of Lake Bonneville was equivalent to all of the freshwater flowing in the world today!
One of the best places to view the Bonneville shoreline is at Point of the Mountain in Draper, Utah. The flat bench extending from Point of the Mountain to the east was formed by waves and currents in Lake Bonneville.

8. Lake Bonneville Flood
About 17,500 years ago, the threshold broke and water spilled out catastrophically into the Snake River drainage.
It is estimated that in less than one year, the amount of water that flowed out of Lake Bonneville was equivalent to all of the freshwater flowing in the world today!

9. Peak discharge during the Lake Bonneville Flood is estimated to 15 million cu. feet/sec. Peak discharge from Lake Missuola Flood estimated to be 30 times greater!

10. Provo Shoreline ~17,000 years agoUT ID NV
Red Rock Pass
Provo Shoreline
Ogden
Delta
Nephi
Provo
Salt Lake
~17,000 years ago
Lake level dropped 340
Feet during the Bonneville
Flood where it stabilized
for 2500 years.
Provo Shoreline ~17,000 years ago
This map shows the Provo level of Lake Bonneville about 17,000 years ago. During the Bonneville flood, the lake dropped about 340 feet to the Provo level where it remained for approximately 2,500 years.
The Provo shoreline is one of the most visible shorelines in the Bonneville basin and is commonly covered by a calcium carbonate deposit called tufa (see slide #19 for a description of tufa).

11. Gilbert Shoreline ~12,000 years ago
Ogden
Delta
Nephi
Provo
Salt Lake UT ID NV
Red Rock Pass
Gilbert Shoreline
~12,000 years ago
About 14,000 years
ago climate became
warmer and drier.
Gilbert Shoreline ~12,000 years ago
This map depicts the Gilbert level of Lake Bonneville about 12,000 years ago. About 14,000 years ago, the climate became warmer and drier and the lake level began to drop. Some evidence exists that the lake almost completely dried up before rising to the Gilbert level about 12,000 years ago.
The Gilbert level is difficult to see because it is only about 50 feet higher than the current Great Salt Lake and is covered in many places by buildings and roads.

12. Great Salt Lake Today ID NV UT Ogden Salt Lake Provo Nephi Delta
Red Rock Pass
Great Salt Lake Today
Great Salt Lake Today
This map depicts present-day Great Salt Lake. Great Salt Lake is the largest remaining remnant of Lake Bonneville. Other relics of Lake Bonneville are Utah Lake, Sevier Lake, and the Great Salt Lake Desert containing the famous Bonneville Salt Flats. The chemical composition of Great Salt Lake is similar to that of typical ocean water. Sodium and chloride are the major ions in the water, followed by sulfate, magnesium, calcium, and potassium.  Although much of the salt contained in the Great Salt Lake was originally in the water of Lake Bonneville, a small amount of dissolved salts is deposited in the lake every year by rivers and numerous small streams that feed into it. As the lake rises, its salinity drops because the same amount of salt is dissolved in more water. In historical time, the lake's salinity has ranged from a little less than 5% (just above that of sea water) to nearly 27% (beyond which water cannot hold more salt).

13. Shorelines of Lake Bonneville at Antelope Island
Provo
Unnamed shoreline
Stansbury
Gilbert
Unnamed shoreline
Shorelines of Lake Bonneville on Antelope Island
Well-defined shorelines are visible at Buffalo Point on the northwest side of Antelope Island. Notice that there are more than four shorelines present. Dozens of unnamed shorelines associated with the oscillations of Lake Bonneville can be seen around the Bonneville basin.

14. Bonneville Shoreline at Point of the Mountain
Bonneville Shoreline at Point of the Mountain (view to the southwest)
This once pristine shoreline near Draper, Utah, is now the site of subdivisions and an expanding gravel pit. The site is also a popular hang gliding and paragliding launch spot. Note the paragliders flying above the ridge on the inset to the right. With increasing building and excavation in this area, pilots are running out of places to land!

15. Lake Bonneville Barrier Bar and Spit Modern Barrier Bar and Spit
Kiawah Island, South Carolina
Lake Bonneville Barrier Bar and Spit
(view to the north, from highway SR 36)
The lower photo is of the Stockton Bar, located in Tooele County, Utah. The Stockton Bar is a composite of barrier bars and spits that formed in Lake Bonneville when it was near its highest level. The Stockton Bar formed much in the same way as the modern barrier bar and spit at Kiawah Island, South Carolina.
A spit forms when sediment is transported along a shoreline and is deposited in a fingerlike extension into a body of water. A barrier bar is simply a spit that has extended all the way across a body of water and has become attached to the shoreline on both ends.
Modern Barrier Bar and Spit
Stockton Bar, Utah

16. COHMAP (1988) Reconstructions
Causes of Pluvial Lake formation in the Great Basin during glacial periods
Lower temperature, less evaporation, from drainage basin and lake surface.
Shift in Jet Stream and storm tracks brought more precipitation to the Great Basin (Related to build up and retreat of the Laurentide Ice Sheet. .
COHMAP (1988) Reconstructions

17. Boundary conditions for COHMAP (1988) climatic reconstructions.

18. African Lake Levels 18 Ka to Present.

19. Lake levels were higher in northern Africa 18 ka years ago because the Jet Stream was displaced south of its present location by build-up of the Fenno-Scandinavian Ice Sheet.
A stable high pressure cell would develop over the Fenno-Scandinavian Ice Sheet displacing the Jet Stream and winter storm track south.
Lake levels in Sub-Saharan Africa were lower 18 ka year ago as the summer monsoon was reduced due to lower solar insolation during the northern hemisphere summer months. H

20. African Humid Period (AHP) is directly related to the strength of the summer monsoon and the 21,000 year precessional cycle.

21. Miocene ( Ma) sapropel bedding cycles exposed marine sedimentary rock in southern Sicily, Italy.
During the AHP, enhance Nile River runoff flooded into the eastern Mediterranean Sea forming a freshwater cap and anoxic conditions and deposition of organic-rich sapropel deposit on the ocean floor (11, years ago). AHP phases occur every 20,000 years through the Miocene.

22. The Great Lakes formed as the Laurentide Ice Sheet retreated from the structural basins that originally formed billion and 570 million years ago

23. Damming of the Clark Fork River by the Purcell Lobe of the CIS caused the formation of a large glacial lake that periodically flooded when the ice dam breached.

24. Strand lines from Glacial Lake Missoula (Missoula Montana)
Strand lines from Glacial Lake Missoula (Missoula Montana). The lake was ~2000 feet deep.

25. Missoula flood boulders deposited in eroded channel near Halverson Bar.

26. Meltwater from the draining of glacial Lake Agassiz has been invoked to cause several climatic cooling events [Younger Dryas (13-12 ka), Preboreal Oscillation (11.3 ka) and 8300 year event] related to weakening or shutting down the North Atlantic Meridonial Circulation (MOC).

27. The presence or absence of marine/fresh waters in the Baltic Sea basin is controlled by 1. the advance/recession of the Scandinavican Ice Sheet, 2. isostasy (due to ice loading and unloading) and 3. eustasy (global sea level change due to ice volume changes).

28. Varves Sequences
A varve is defined an annual sediment layer. Varves are most commonly deposited in glacial lake (lacustrine) deposits, but also in some marine environments. Varves form because of seasonal or annual variations in deposition responsible for contrasting layers within one year.

29. Glacial Varves
A varve or annual couplet is composed of a light-colored melting season or "summer" layer and an overlying dark-colored non-melt season or "winter" layer.
The “summer” or melting season layers are composed of multiple micro-graded beds or laminations that often show a general fining upward and may grade into the “winter” layer above.
The non-melting season or “winter” layers (dark) are composed of very fine sediment, usually >90% clay. The winter layers are often gradational below with the top of the preceding summer layer and are sharply truncated above at the base of the following summer layer.

30. Glacial Varves
Varve thickness will vary depending upon the sedimentation rate into the lacustrine basin.
Generally, ice-proximal deposition will result in thicker varve units, particularly during summer ablation season, such as shown in the image on the left.
Ice-distal deposition will tend to form thinner varve units, such as shown in the image on the left.

31. Varve chronologies can be determined by counting varve couplets usually using a marker bed or varve within the sequence. The sequence above represents 36 varve years. Note the dropstones in the varved sediment from ice-rafted sediment.

32. Varves can be used to determine the retreat rate of an ice sheet in a glaciated region where basal till underlies varve sequences over the transgressive retreat area.

33. Varve chronologies can be used to determine the time-transgressive deglaciation history of a region providing a marker bed or isochron (ash layer, distinct depositional event) is preserved in the respective varve sequences.

34. Varve chronologies can be used to calibrate the 14C time scale with calendar years. Lake Suigetsu, Japan possesses as 60,000 year continuous varve chronology that is consistent with the tree ring and U-Th calibrations.