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Yosemite Falls Facts and Geology


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Yosemite Falls Picture Yosemite Falls Heights
Fall Feet Meters Comparison
Upper Fall 1,430 435 Sears Tower, Chicago, Illinois
Middle Cascades 675 205  
Lower Fall 320 98 Length of a soccer field
Total 2,425 740 Sears Tower plus Eiffel Tower, Paris, France

Rank:

Terminology Trivia:

The term falls is best used for waterfalls with multiple drops: Yosemite Falls, Sentinel Falls, Snow Creek Falls, etc. However, the term fall is more properly used when there is only a single drop: Upper Yosemite Fall, Lower Yosemite Fall, Vernal Fall, Bridalveil Fall, etc.

Flow and Volume:

Yosemite Creek has no gauging station for accurate flow measurements. Hydrologists have estimated an average spring flow of 300 cubic feet per second (cfs). There's approximately 8 gallons per cubic foot of water

The Yosemite Falls by Carleton E. Watkins, circa 1865-1866 from The Yosemite Book (1869)
The Yosemite Falls by Carleton E. Watkins, circa 1865-1866 from The Yosemite Book (1869).
which converts to 2,400 gallons/second or 9,000 liters/second.

Principally snow melt feeds Yosemite Creek and Falls. A good proportion of this watershed is bare granite with limited soil and few lakes for water storage which would prolong a greater water flow into late summer and autumn. So it roars in spring and whimpers later in the season.

In contrast, the watershed of Bridalveil Fall maintains a greater flow later into the season although its watershed is approximately only 60% the size of Yosemite Creek's watershed. There are several reasons for this apparent anomaly:

Watershed Area:

Computed as area above brink of Upper Fall.
Source: Jan VanWagtendonk, Research Scientist, using GIS (Geographical Information System), March, 1991.

Brief Geology Story for Yosemite Falls:

Waterfall Heights:

The reason the tributary streams to the Merced River in Yosemite Valley have their great height above the valley floor (hanging valleys) is due to differential erosion. That is, the valley's rivers and glacierscut down into the rocks more quickly where the valley now lie, than did other tributary streams and glaciers. Tributary drainages were left behind at higher elevations. The valley was cut more deeply and quickly because:

  1. The rivers had more water and the glaciers had more ice, because of the greater size of the upstream watershed, thus giving them more erosive power.
  2. These rivers and glaciers had more speed since they flowed down the western Sierran slope, which also provided them more erosive power to cut downward. Tributary streams flowing in from the north or south are relatively less steep since they flowacross the western slope.
  3. The valley's rivers and glaciers were cutting down into granites containing major, east-west trending straight cracks (i.e. joints). These joints run in the same general direction (east-west) as the westerly flowing rivers and glaciers. These joints gave an advantage to the rivers and glaciers for more rapid and extensive erosion. In contrast, the tributary streams cut across these east-west joint systems thus gaining little advantage from them for eroding downward. (Note: These east-west joints are atypical in the Sierra where the master joints trend north-south as the range does. Geologists debate the reason for this.)

Vertical Cliffs and Waterfall Alcoves:

Nearly all the sheer cliffs form where vertical joint systems allow rocks toflakeoff thus exposing relatively-clean, nearly-vertical surfaces. Rocks continue to flake off and the cliffs have receded significant distances since glacial times. The extra water (and winter ice) provided by tributary streams have greatly accelerated cliff recession where waterfalls pour over. All major falls in the valley have created their own recessed alcoves in a way that glaciers could never have carved such alcoves. Both Yosemite's Upper and Lower Falls sit in such recessed alcoves.

Why does Yosemite Falls have 3 levels or drops?

This is again due to joint systems (groups of linear cracks). This time the joints are running horizontally. Two horizontal joint systems interrupt the vertical joint systems. One horizontal joint system is near the base of the upper fall and the other near the brink of the lower fall. Therefore, vertical weaknesses (forming cliffs) meet horizontal weaknesses (forming benches). These two horizontal joint systems are clearly visible running both left and right away from the falls area a quarter mile or more. They are highlighted by the increased amount of vegetation that is encouraged by more ledges, cracks and soil at those locations.

Further Information

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