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| Aqua/Modis Satelite Image of the Great Salt Lake on 4 Aug 2024 |
It is not uncommon to see reports of recent or long-term trends in the Great Salt Lake characteristics based on lake elevation. This is a quantity that is measured at three locations, two with a fairly long record. The first is Saltair in the south arm of the great Salt Lake. The second is Saline in the north arm.
While convenient, they often differ by a decent amount. This is because the lake is separated by a rock fill railroad causeway which limits the transfer of water between the two halves. This results in differences in lake elevation (the south arm is typically higher), salinity (the north arm is saltier), and even color (see above; for an explanation see https://wildlife.utah.gov/gslep/about.html.)
However, with a little information about the lake bathymetry (i.e., the underwater terrain of the lake), one can take the elevations from Saltair and Saline, estimate the area and volume of each half of the lake, and combine them into a total area and volume for the lake. Thanks to work by Utah State University and the USGS, tables to convert from elevation to area and volume are available at https://pubs.usgs.gov/of/2005/1327/PDF/OFR2005-1327.pdf and https://pubs.usgs.gov/of/2006/1359/PDF/ofr2006-1359.pdf, respectively. These are based on 1/2 foot lake elevation intervals.
Based on recent readings rounded to the nearest half foot, I thought I would look at changes from August 2022, when the lake was approaching its historical minimum elevation to August 2024, the summer after two above average snowfall years. Here's what I got.
Aug 2022
Saltair/Saline Elevations: 4189.6/4189.4 ft
Estimated Lake Area: 605,242 acres
Estimated Lake Volume: 7,419,322 acre-feet
Aug 2022
Saltair/Saline Elevations: 4193.6/4191.8 ft
Estimated Lake Area: 649,320 acres
Estimated Lake Volume: 9,528,374 acre-feet
So, in this two year period, the lake area has increased about 7% and the volume has increased about 28%.
Feel free to pull the numbers and check my math. However, one can see why the the former has gone up more slowly as a percentage based on the graph below which shows the volume and area as a function of lake elevation in the south arm (also known as Gilbert Bay). Note that the slope of the area curve becomes =greater above about 4194 feet. Basically, the lake "bathtub" has steep walls up to 4195 feet, so a given volume of water increases the area less than at higher elevations where the "bathtub" walls are more gentle.
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| Source: https://www.usgs.gov/media/images/great-salt-lake-hypsographic-curve |
I've used the words "estimated" above because lake bathymetry does have some uncertainties, I'm rounding off noisy lake-elevation data, etc.
If someone knows of a website that provides data on area and volume calculated based on the elevation data in the two halves of the lake, please share in the comments below. I think that would be extremely useful to have updated monthly to better understand what is happening in each half and for the lake as a whole.
Interesting topic today. Being an old armchair GSL observer, I’ve been pondering the climatological implications of Lake Bonneville becoming the Great Salt Lake. As near as I can tell the maximum elevation of Lake Bonneville was about 5200 feet, assuming the Shoreline Trail indicates full tub. The breach at Redrock Pass, Idaho 14500 years ago dropped the lake level about 400 feet to an elevation of about 4800 feet which puts it somewhere in the middle of the UofU. So, in 14500 years the lake has dropped another 600 feet to its current level. That would indicate a hot, dry climate for at least the last 14500 (?) years. It would be interesting to know how much of the decrease is anthropogenic and how much is a continuation of the long term trend.
ReplyDeleteI'm not an expert at paleoclimate or the demise of Lake Bonneville, but it is my understanding that the decline from the Provo Shoreline to something close to the average elevation of the GSL today did not occur gradually over the past 14,500 years. Instead, the drop to elevations near those of the modern GSL occurred from 15,000 to 13,000 years ago. This was during a period of warming during the transition from the last glacial maximum to the holocene, the current geologic epoch, which began about 11,000 years ago.
DeleteThe Holocene has been characterized by a relatively stable climate. Human caused warming, however, is changing that. This human caused warming is not a continuation of a long term trend and more rapid and much larger than any of the climate variations that have occurred previously during the Holocene (back at least 10,000 years).
What about the sun?
DeleteThanks for your reply. That would seem to make sense. Digging a little deeper, it would seem that human caused climate change began with the Industrial Revolution in 1750 or thereabouts. The Great Acceleration, supposedly pegged to the year 1950, is the end of the Holocene and the beginning of the Anthropocene. Are there any records of the GSL’s elevation in 1847 when the pioneers arrived? I’m sure there is a graph of lake levels since their arrival. Might also be interesting to superimpose the increase in Utah’s population on the lake level graph. Not sure how one would incorporate the impacts of accelerating climate change.
DeleteYes, what about the sun?
DeleteThe sun is not responsible for recent climate change. The Earth has been warming in recent decades despite a slight decrease in the amount of solar energy reaching the earth. In addition, the Earth's atmosphere responds differently to variations in solar output than an increase in greenhouse gas forcing and the patterns of warming in recent decades are consistent with greenhouse warming and not consistent with solar warming.
In the past though, the warming from the Last Glacial Maximum to the early Holocene was triggered by changes in the distribution and seasonality of solar energy received by the Earth related to characteristics of the Earth's orbit and tilt, with feedbacks due to melting ice sheets and increasing greenhouse gas concentrations amplifying this warming. Those processes were natural, in contrast to warming in recent decades, which is human caused.
DeleteAre there any records of the GSL’s elevation in 1847 when the pioneers arrived?
DeleteYes. Historical records of the GSL elevation begin in 1847. There is a graph at https://wasatchweatherweenies.blogspot.com/2023/05/great-salt-lake-update.html that shows the data back to October of that year.
The primary impact of humans on the elevation of the Great Salt Lake has been due to water diversion. More at https://digitalcommons.usu.edu/wats_facpub/875/.