Wednesday, October 24, 2018

How Much Lake Effect Did Lake Bonneville Produce?

It is a question that I am asked frequently, how much lake effect did Lake Bonneville produce?

Lake Bonnevile was an ancient lake that existed during the last ice age and covered much of the Bonneville Basin of Utah, Nevada, and Idaho.  About 14,500 years ago  the lake reached its highest level, burst through Red Rock Pass, and flooded southern Idaho and eastern Washington via the Snake River, resulting in a drop in lake elevation to 300 feet.  The Great Salt Lake is a remnant of Lake Bonneville.

At high stand near the end of the ice age, Lake Bonneville was over 1000 feet deep and glaciers existed in 15 mountain ranges within its drainage basin.  The bulk of this glacier ice was in the Wasatch and Uinta Mountains.

Lake Bonneville at maximum extent (blue) with mountain glacier systems in transparent light blue.
Source: Laabs and Munroe (2016)
We don't really have much knowledge about the effects of Lake Bonneville on local climate.  Geological studies indicate that Lake Bonneville may have affected the glacier mass balance (likely through greater snow accumulation) in downwind mountain ranges, with glacier equilibrium lines being lowest in the Wasatch Mountains and higher upstream in the Deep Creek Range and farther downstream in the Uinta Mountains.  This pattern cannot be explained by the distribution of modern precipitation across the region.  

Reconstructed glacier equilibrium line altitudes.  Source: Laabs and Munroe (2016).
For those of you who miss the good old days, below are a couple of maps illustrating the ice extent in a heavily glaciated portion of the Wasatch Range and the Uinta Mountains.  This represents maximum ice extent, although evidence suggests that the terminus of glaciers in Little Cottonwood and Bells Canyons likely extended to the base of the Wasatch Range near the time of the Lake Bonneville high stand.  What a scene that would have been.  
Pleistocene ice extents in the Wasatch Range.  Source: Laabs and Munroe (2016)
Pleistocene ice extents in the Uinta Mountains.  Source: Laabs and Munroe (2016)

A few years ago, one of my students, John McMillen, stuck Lake Bonneville into one of our simulations of a Great Salt Lake effect snowstorm.

Not surprisingly, this results in a significant increase in the coverage and the intensity of precipitation, although in this northwesterly flow event, Salt Lake Valley and the south-central Wasatch Mountains around lower and middle Little Cottonwood Canyon, receive the most precipitation.  There are also some changes in storm characteristics, which we'll skip over here in the interest of time. 

That was all fine and dandy, but if we really want to understand the impacts of Lake Bonneville, we have to do quite a bit more since one event tells us little about what to expect over a season, decades, or centuries.  

First, we need to account for the different large scale circulation that existed during the last glacial maximum.  Global and regional climate models can be used to do this, although to my knowledge, this has never been done using regional climate models with sufficient resolution to adequately resolve the influence of Lake Bonneville and surrounding terrain.  

Second, we need to couple the regional climate model with a lake model that can simulate seasonal variations in lake temperature and potentially ice coverage.  The Great Salt Lake is a very unusual lake in that it is hypersaline, very shallow, and never freezes.  As a result, it warms and cools very quickly.  A large lake like Lake Bonneville would cool more slowly in the fall and early winter and warm more slowly in the spring.  This would shift the seasonal distribution of snowfall such that instead of maxima in lake-effect in the fall and spring, as occurs with the Great Salt Lake, it would instead be in December or January.

Third, we would probably need to include Lake Lohontan, another large lake that existed during the last ice age over Nevada.  Multi-lake effects are common in the Great Lakes and I hypothesize the could have been important over the Great Basin during the last ice age.  

Those are a few of the issues at play.  I have always been interested in a modeling project that would do this.  I confess that my motives are not purely scientific.  It simply sounds like fun.  Plus, one could take those model simulations and put together some amazing visualizations of what northern Utah looked like at the end of the last ice age.  What a hoot that would be. 

This is the kind of project that might be hard to get funding for, but is ripe to support with a magical discretionary account.  If you won the $1.6 billion dollar lottery last night, give me a call!


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  2. Fascinating. I would love to see a study done on this. What exactly would make a Bonneville lake-effect storm different than a Great Salt Lake effect? Perhaps you could study a Provo-level lake as well, since that's the highest possible lake level today.

    Also, I saw in a article that the East Pacific "blob" is back. What, if anything, does that mean for the snow outlook this winter?

  3. Topical webcomic: