Yosemite's Secrets - How Deep Is Tenaya Lake?

[Kris Corey]

Over the winter months while researching material for Yosemite Audio Adventures I stumbled on some Yosemite trivia that simply blew my mind & I just have to share it!

It all began at Tenaya Lake in Yosemite National Park. Playing on the frozen water of Tenaya lake was one of those "once in a lifetime experiences" and while I was scooting around on the ice a female tourist asked if I knew how deep Tenaya Lake was?

I did not, I was taken back, I pride myself on knowing most everything about this park! It's a simple question but I had no idea.

The steep slope on the opposite shore makes it appear deep yet I remembered some stumps somewhere and thought, well, that makes it appear shallow.  A new Yosemite trivia question to investigate, excellent!

So, that's how this all began, with the simple question of "How deep is Tenaya Lake?" What a cool can of worms!

Okay, look at the pic & notice how the Lodgepole Pines grow almost right down to the waters edge here at Tenaya Lake.

Okay, so here's a few facts you need to know;  Lodgepole pines can't grow in water. So, in order for these trees to colonize the ground had to be dried out for a while. Lodgepole pines roots can only handle a few weeks of being submerged in water.

And, the answer to the question of "How deep is Tenaya Lake?" is:
"A little over 100 feet."  (~101'- ~110') According to the Park Service who also forwarded me an article regarding the "stumps" in Tenaya Lake.

The other thing you need to know here is that Tenaya Lake was created when the glaciers receded about 10,000 years ago.  It is dammed by a glacial moraine and a stream has created a stable spillway that normally overflows each year during the Spring snow melt. This water travels down to Mirror Lake via Tenaya Canyon. In recent history the water levels have varied somewhat with the Spring snow-melt but normally, the lake maintains fairly constant levels year to year. (At least in our lifetime.)

Now, here's where things get interesting! Remember those stumps you've seen in Tenaya Lake? They are not stumps at all! They are huge snags! Dead Lodgepole Pine trees still rooted in the lake bottom!  These snags are standing in anywhere from 26 to 62 feet of water! 

The snags are actually from two distinctly different periods in time, which creates some confusion, but quite simply, some of the dead trees were about 70 years old when they died and others were about 140 years old. They lived and died about 900 years ago (avg), during the medieval period in history ~ 1028 - 1386 AD.

Bottom line: In order for the first batch of trees to colonize on the banks of Tenaya Lake the water had to have been ~ 42 feet below it's spillway for at least 70 years. Then, in order for the second batch to colonize at a later date the lake had to have been about 36 feet below it's spillway for a minimum of 140 years! 

Now, the real clincher here is that these two time periods were only 100 years apart!

According to this very convincing article by Scott Stine, California had two major droughts during the medieval time period in history. The first one lasted 220 years and this is when the first batch of Lodgepole Pines were able to colonize the dry lake shore.

Amazingly, this 220 year drought was followed by 100 years of very wet weather, enough to start filling Tenaya Lake and killing that first batch of trees.

Well, then came a second drought. This one lasted about 140 years and the second batch of Lodgepoles were able to colonize on the dry shores of Tenaya Lake. Since that time the weather has stabilized to the point where we see a year or two with decreased precipitation as a disaster.

In the last 140 or so years we've experienced 2 droughts that we define as major. They each lasted 6 - 8 years and each year Tenaya Lake has overflowed its spillway during the Spring snow melt. At no time during either of these droughts did Tenaya Lake fall below 3 feet of the spillway.

In order for these submerged Lodgepole Pines to have grown here, the lake level had to be about 45 feet below it's spillway for over 70 years! Then, only one hundred years later, the lake level was at about 36 feet below its spillway for over 140 years after that!

Incredible! We are talking major droughts! Mother Nature is always so impressive!

If you'd care to read the article by Scott Stine you can download it @
http://blog.lib.umn.edu/stgeorge/geog5426/2010/10/09/Stine%20Nature...
I've done my best to translated it from scientific lingo to regular English but please contact me with any corrections @ [e-mail]