Tahoe Quarterly

Tahoe's Drowned Trees 

by Leo Poppoff 

A severe and prolonged drought hit the Tahoe Basin hard in the 1930s, during which time The Lake’s water level dropped below its natural rim for six consecutive years. The biggest decline occurred in December 1934, when Tahoe’s level fell 1.21 feet below the rim—and a mysterious clump of well-rooted tree stumps poked through the water’s surface along the South Shore. UC Berkeley, scientist Samuel Harding cataloged a cluster of eleven such stumps near Tallac. And that’s where the matter stood for some three decades.

   In 1965, using radio-carbon dating techniques, Harding made an amazing discovery: The tree remnants were between 4,000 and 5,000 years old. Twenty years later, archeologist and Donner Lake resident Susan Lindstrom, using SCUBA gear, relocated five of those stumps, the largest of which was 3.5 feet in diameter and 7 feet tall. Samples from one tree’s exterior dated back 4,520 years; innermost sections showed it to be 4,870 years old. The tree could have been 350 years old before it “drowned.” 

What all this implies is that Lake Tahoe’s water level was much lower 4,500 to 6,300 years ago, and stayed so long enough for trees to root and grow for several hundred years.

   Scientists have argued—sometimes vigorously—over what caused this series of events. Were devastating droughts followed by epic rains? Did tectonic activity lower the southern part of The Lake? Or did sediment buildup on the natural rim at Tahoe City raise Tahoe’s water level? The drought theory has the most evidence to confirm it, although the tectonic explanation still has its fans.

   The end of the last Ice Age, around 12,000 years ago, was the start of the current geological period, the Holocene. Early Holocene was still cool and moist while the climate warmed and glaciers melted. Mid-Holocene, roughly 4,000 to 7,000 years ago, was much warmer and drier. During that time, many lakes in the Western Great Basin dried up, but Lake Tahoe and Pyramid Lake survived. The late Holocene, the past 4,000 years, marked a return to cool-moist climates, punctuated with intermittent droughts—and the restoration of many Great Basin lakes.

   Most of the drowned trees date to the mid-Holocene, although some appear to have originated from a couple hundred to 1,200 years ago, suggesting more recent serious droughts.

   One such period, from roughly 850 AD to 1150 AD, is known as the “Medieval Warm Period,” during which time Vikings were able to explore and build settlements in such currently cold places as Greenland and Northern Canada. Vineyards flourished in England. A few hundred years later, from about 1500 AD to 1850 AD, the climate turned bitter cold, with unseasonable snows and bracing persistent rains. It’s known as the “Little Ice Age.”

   Because the stumps are so well preserved in Tahoe’s cold and oxygenated waters, it’s logical to conclude that the droughts were followed by wetter periods, drowning the trees before they rotted. Phil Caterino, the founder of Tahoe Divers Conservancy, has spent many years diving in Sierra lakes and studying sunken trees in Lake Tahoe, Fallen Leaf Lake and Yosemite’s Tenaya Lake. He believes that the sequence of very dry and warm periods followed by cool and very wet years can be confirmed by studying ancient avalanche debris in the Basin.

   Sonar mapping of Lake Tahoe’s bottom has revealed many landslides. Caterino suggests that these were avalanches caused by severe flooding during intense wet periods on the heels of low lake levels. Fossilized wood rat midden found at Cave Rock adds credence to the supposition.

   Global climate is warming once again. Perhaps closer study of the conditions that caused the drowning of trees in Lake Tahoe, and elsewhere in the Sierra, could provide insights into future weather patterns.

A retired NASA atmospheric physicist, Leo Poppoff considers his writing “an ideal avocation for a retired scientist.”