Born of glaciers

Three months of camp life on Lake Tahoe would restore an Egyptian mummy to his pristine vigor, and give him an appetite like an alligator.–Mark Twain, Roughing It (1872)

p1020578_2 When Mark Twain first laid eyes upon Lake Tahoe in 1861, he thought it “must surely be the fairest picture the whole earth affords.” More than a century and a half later, that opinion is still shared by another Missouri boy, and though I would gladly welcome three months of camp life over one week at a ski resort, I nevertheless remain confident that my vigor will be fully restored by the time I return to work next Monday. The journey that began some days ago in the foothills of my beloved, ancient Ozark Highlands has today taken me to one of the youngest of landscapes to grace Lake Tahoe – Emerald Bay. I have written previously about Lake Tahoe (one year ago almost to the day) in a post that also featured photos of Emerald Bay and its only island, the iconic Fannette Island. p1020596_2 The Tahoe Basin itself is a relatively young landscape, forming within the last 5-10 million years as the basin floor dropped between two uplifted blocks. Volcanic flows in the valley on the north side of the present lake dammed the valley to form the lake, whose level has fluctuated drastically over time during the past 2 million years as Pleistocene glaciations have repeatedly damned the Truckee River that drains the lake into the lowlands of Nevada. At maximum, the level of the lake approached 7,000 feet in elevation – nearly 800 feet higher than today. p1020577_2 It was the last of these glacial events – near the end of the Pleistocene just 10,000 years ago – that gave birth to Emerald Bay. Unlike the “ice sheets” that spread out across much of the continent, the ice age here manifested itself as individual glaciers that formed at the highest elevations and carved out individual valleys as their crushing weight ground them inexorably downward. The elongated shape characteristic of such glacial valleys is seen not only in Emerald Bay, but in the adjacent Fallen Leaf Lake and Donner Lake in the north as well. John Muir alludes to this glacial birth in a description of Emerald Bay that he wrote in his private journal in 1888:

Emerald Bay is about two miles long. Its mouth is nearly closed by a terminal moraine; the sides are formed by lateral moraines. The left lateral is very striking, well formed, three or four hundred feet high where it joins the shoulder of the mountain, timbered with pine and spruce¹ sparsely on the grayish slopes.

¹ Actually firs, of the genus Abies.

Upper Eagle Falls from Eagle Lake - part of a ''glacial staircase'' above Emerald Bay

Upper Eagle Falls from Eagle Lake - part of a

Unfortunately, the very existence of Lake Tahoe is under threat. While the mountain building processes that created the Sierra Nevada have ceased for now, the erosive forces caused by weathering continue unabated. The Sierra Nevada range is being gradually worn down, and Lake Tahoe is filling with sediment at an average rate of about 1/10th of a millimeter per year. At this rate, Lake Tahoe will become a meadow in just over 3 million years.[/humor]

Lake Tahoe facts:

  • It is 22 miles long, 12 miles wide, and holds about 40 trillion gallons of water – enough to cover the entire state of California to a depth of 14.5 inches!
  • Maximum elevation of the lake surface is about 6,229 feet above sea level.
  • The lake is drained by the Truckee River, one of a few rivers that run inland to the desert rather than towards the ocean.
  • It is the third deepest lake in North America, with an average depth of 989 feet. However, the deepest point is about 1,645 feet.  It is the largest lake in North America above 600 feet elevation.
  • Surface temperatures can reach as high as 75°F in summer, but at depths below 600 feet the water remains a constant 40°F.
  • Lake Tahoe does not freeze over, although Emerald Bay has formed complete ice cover at least three times during the 20th Century and partial cover in more years.

More Lake Tahoe facts can be found at the U.S.D.A. Forest Service, Lake Tahoe Basin Management Unit FAQ site and at Tahoe Topics and FAQ’s, by David C. Antonucci (2004).

Copyright © Ted C. MacRae

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11 thoughts on “Born of glaciers

  1. I don’t think I will still be around then to see it become a meadow. A fantastic post Ted of a very beautiful place. This is one of the things I miss here in SA, the wide open spaces. Everywhere you look new building are going up and open land is getting difficult to find. In 100 year’s time, where will someone like me be able to go to find wild insects and birds. Thank goodness for the private game reserves, they will be all that is left – then again, looking at the political climate, I am not so sure about that either. 😦

  2. there was a monster landslide that also sculpted the western north part of the lakeshore. deep images of the lake floor by usgs show debris strewn across the lake bottom from this slide.
    it originated near homewood, and caused the curved bay in the west shore. Age is hard to determine, but it is pleistocene in general. pax t

    • Terry — thanks for your added insight. I just yesterday purchased National Geographic’s USDA Forest Service map of Lake Tahoe Basin, and I believe I see what you are referring to. It’s fairly easy to imagine the profile of the lake as parallel sided if that bay were not there.

  3. Ted, nice work on Tahoe including the two posts on the trees. Very professional photography. One question and a few comments:

    Where did you get the rendering of the glacial action at Emerald Bay and Cascade Lake?

    Unfortunately, a couple of your Tahoe “facts” are not quite correct, particularly the link to BlogTahoe on freezing (it’s all wrong).

    The Lake holds about 40 trillion gallons of water, enough to cover the state of California to a depth of 14 ½ in. Between the regulated high and low water levels, the volume of water in Tahoe can vary by 243 billion gallons. Tahoe is the largest lake by volume above 600 ft. elevation in the USA.

    Maximum lake level is 6229.1 ft Lake Tahoe Datum, which equates to 6227.96 NGVD of 1929, or roughly sea level for laypersons. (Lake Tahoe has its own definition of sea level.) Average elevation is about 6225 ft above sea level.

    Below an average depth of 600 ft, water temperature is a near constant 40˚F. During July and August, surface temperature can reach 75˚F. In the coldest months, the lake surface temperature lowers to 40˚F. Lake water temperatures have changed from the old measurements due to global warming.

    You may want to change the BlogTahoe link to point to Thomas Bachland at and go to the Lake Tahoe Facts pdf. The explanation on freezing is brief but you can get a more detailed paper from me by sending me your email address.

    Excellent work on the Trees of Tahoe and Born of Glaciers!

    • Hi David,

      Many thanks for setting the facts straight. The glacial rendering is from a display board at one of the Emerald Bay overlooks – I just took a photograph of it.

      As you suggested, I’ve changed to BlogTahoe link to your quite informative “Lake Tahoe Facts” pdf.

      I would love to see a more detailed explanation of the freezing phenomenon – contact me via the link at the top of this page (“Contact”) and I’ll send you my email address.

      Thanks for stopping by – I appreciate the benefit of your expertise and your kind comments about my posts.


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