High Water in Yosemite III

We continue our journey through Yosemite Valley during the peak runoff last week (part I here, and part II here), when the Merced River exceeded 7,000 cubic feet per second, and reached flood stage. Numerous meadows and trails were underwater, and it was a wonderful thing to see! Above is the view from in front of the chapel at Old Yosemite Village. The slope on the right is the lower part of the Three Brothers, with the Cathedral Rocks in the distance.

And above we have a flooded portion of the meadow at the base of El Capitan. Once again, we are looking at the incredible Cathedral Rocks with the Cathedral Spires on the left.

The gaging station that measures the discharge of the Merced River is just upstream of Pohono Bridge. The problem with bridges is that we tend to put them at the narrow parts of river channels. When the floods come, the bridges can cause a bottleneck effect, having all kinds of implications upstream and downstream. Some of the bridges have been redesigned in recent years to allow the river to flow in a more natural pattern and to stabilize bank erosion.

As noted in the previous posts, floods are not a particular problem for the natural ecosystems of the valley. The ecosystem developed under a seasonal pattern of flooding and drought. The floods can be a minor inconvenience to hikers on the valley floor, as in the picture above where the riverside trail is flooded.

Trees that grow too close to the river will have their roots inundated. If the flood lasts for any period of time, the trees will suffocate and die. Usually the high water backs off within a few days. Today, a week after my trip, the river is flowing at 3,160 cubic feet per second, half of what it was a week ago, but still about 50% above normal for the middle of June.

Update: Martha at Martha's Musings was in Yosemite at the same time. See some nice pictures here.

Staring into the Abyss #3 - Yosemite as you (maybe) have never seen it

If you go back to my original post and series debut of the under-rated places of Yosemite Valley, you will remember the classic view of Yosemite Valley from the Wawona Tunnel exit. This picture is looking west from Taft Point on the rim of the valley back towards the Tunnel View, with the Cathedral Rocks and Spires forming the dominant cliffs in the center of the photo.

El Capitan Meadow is visible on the valley floor. One of the most prominent Tioga Stage glacial moraines lies just west of the meadow. It dates to about 13,000 years before present. For thousands of years, natural wildfires and intentional burnings by Native-Americans cleared the conifers from the valley floor, and over time it evolved into an open oak woodland with wide meadows and a few widely scattered conifer trees. The size of meadows in Yosemite Valley has dramatically decreased in the past century. Josiah Whitney and his crew calculated meadow area in 1866 to be 745 acres. By 1937, meadow area had dwindled to 327 acres. Today, meadows cover 65 acres, leaving only 6.8% of the original 1866 meadow area. With the advent of national park status, fires were suppressed and the shade-loving conifers flourished. The forest is now dense with young trees, and the possibility of disastrous wildfires is very real.

The distant skyline shows the relatively gentle westward slope of the mountain range, leading into the Central Valley. The mountains have risen by fault motions on the eastern margin of the range, leading to a westward tilt that has mostly developed within the last 9-10 million years.

Under the Volcano: Changing the Emphasis

The classical and long-familiar view of Yosemite Valley from the end of the Wawona Tunnel has become so iconic that it is easy to forget how spectacular the individual elements of the view would be in any other setting (see Standing Underneath Volcanoes from a few days ago) . Since getting my first digital camera in 2001, I have been to Yosemite Valley 22 times, and I always take the same picture! It's true that every visit is different, with different clouds and light conditions, but it is hard to stand in front of one of the great panoramas of the world without trying to fit it all into a single picture. So, during the last few visits I tried to zoom in on a few of the pieces that make for such a rich tapestry.

Today, our view is of the lowermost Cathedral Rocks next to Bridalveil Fall (which at 620 feet provides the scale for the picture). The triangular shape of the cliff results from intersecting vertical joint sets. The cliffs are composed primarily of El Capitan granite (about 102 Ma), which is a coarse-grained, white to light-gray biotite granite and biotite granodiorite containing quartz (gray glassy looking grains), orthoclase feldspar (white grains), and biotite mica (black grains)..


Exfoliated Sentinel Dome can be seen at the top of the photograph. The Glacier Point Road pulls to within a quarter mile or so of the summit, and it is an easy climb for an incredible payoff of a view (see some future post!).


Update on the Earthquake Watch: didn't feel any of them today, but the Historical Geology Class got to see an incoming quake on the seismometer this evening. It was probably the 6.5 magnitude quake in the Andreanof Islands in the Aleutian chain. 29 years and 364 days to go....