Lake Tahoe Quakes & Tsunamis
At a recent lecture sponsored by the
Squaw Valley Institute, Dr. Schweikert,
Professor of Geology at the University of Nevada, Reno, discussed the geological
structure and evolution of the Tahoe Basin. Of the clearly identified earthquake
faults running approximately north-south through the region, two major faults
pass through the lake and one major fault is located west of the lake.
It is now believed that McKinney Bay, on the west shore, was probably formed
by a giant land collapse and may have generated a tidal wave in the lake as high
as 90 feet, that sloshed back and forth from shore to shore for as long as 12
hours.
Although significant earthquakes are a near certainty sometime in the future,
the chances of this happening sometime in our lifetimes is remote. No need to
hurry out and purchase earthquake insurance!
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Lake Tahoe's Volcanic Origins
Although it is commonly believed that Lake Tahoe is of volcanic origin, the
Lake Tahoe Basin was actually formed by faulting—fractures in the earth’s crust
allowing blocks of land to rise and sink. This occurred over several million
years as the Sierra Nevada mountains were rising from a shallow sea. Two
principal steep faults evolved, the eastern margin created the Carson Range
while the Sierra Nevada mountains rose on the western side. From the “up thrown”
fault blocks the highest peaks in the Lake Tahoe Basin originated. Freel Peak
(10,891) , Monument Peak (10,067) the present Heavenly Valley Ski Area, Pyramid
Peak (9,983) in Desolation Wilderness, and Mt. Tallac (9,735) which has a fault
running at its base.
A lake formed near the southern and lowest part of the basin, fed by snow, rain,
and draining creeks and rivers. The lake level increased in depth until it found
an outlet, then near the present town of Truckee. Several active volcanoes
poured lava into the basin, eventually damming the outlet. The waters rose
again, several hundred feet higher than the present level. Finally, a new outlet
was cut, just east of one volcano, Mt. Pluto, the present location of Northstar
Ski Area. Cave Rock on the east shore of Lake Tahoe is the eroded remains of
another volcano that once poured lava into the basin. Its “cave" is wave cut, a
relic of the ancestral and much bigger Lake Tahoe.
During the Ice Age, glaciers scoured the surrounding landscape to the shape what we
see today. These rivers of ice followed pre-existing V-shaped stream canyons,
carving them as they moved downward to smooth U-shaped valleys. Emerald Bay,
Cascade Lake, Fallen Leaf Lake and the Echo Lakes now fill some of these
U-shaped valleys. Moraines, glacial debris left behind, blocked the outlet
again, changing it to the present Truckee River outlet at Tahoe City.
How large is Lake Tahoe?
Lake Tahoe is about 22 miles long and l2 miles wide with 72 miles of shoreline.
The surface area covers 191 square miles. Lake Tahoe is the third deepest lake
in North America and the tenth deepest in the world. Its greatest measured depth
is 1,645 feet and averages 1,000 feet. (In North America, Crater Lake in Oregon
at 1,930 feet and the Great Slave Lake in Canada at 2,010 feet are deeper.) The
floor of the basin is near the 4,580 foot elevation, lower than the surface of
the Carson Valley to the east! Lake Tahoe’s average surface elevation is 6,225
feet above sea level, making it the highest lake of its size in the United
States. Its exact elevation, controlled by a dam in Tahoe City, depends on how
much water flows in from the mountains and how much is let out into the Truckee
River.
Unlike most bodies of water in North America, Lake Tahoe’s water does not
eventually flow into the ocean. The Truckee River, its only outlet, flows east
through Reno and into Pyramid Lake in Nevada.
How cold is the water?
The water temperature near the surface generally cools to 40 F to 50 F (4-1/2 C
to 10 C during February and March, and warms to 65 F to 70 F (18 C to 21 C)
August and September. Below 600-700 foot depths, the water temperature remains a
constant 39 F (40 C).
How much water is in Lake Tahoe?
The water in Lake Tahoe could cover a flat area the size of California by 14
inches. This is also enough to supply everyone in the United States with 50
gallons of water per day for 5 years. And believe it or not, the amount of water
that evaporates from the surface of Lake Tahoe every year could supply a city
the size of Los Angeles for 5 years.
Why does the lake stay so clear?
The lake is so clear that objects can be seen up to depths of 120 feet. One
reason is that 40% of the precipitation falling into the Lake Tahoe Basin, lands
directly on the lake. The remaining precipitation drains through the decomposed
granitic soils found in marshes and meadows, creating a good filtering system
for water. These soils are relatively sterile, therefore water filtered through
them enter the lake relatively “pure”. Another contributing factor is the
exportation of all sewage from the Lake Tahoe Basin. Although Lake Tahoe is
going through a natural aging process (succession), filling up with sediments
like any other lake, additional amounts are washing into the lake as slopes are
cleared for construction . Each sediment particle carries nutrients which
stimulate algae growth that will eventually cloud the famous clarity of the
lake. Development of marshes and stream zones, such as the Tahoe Keys, prevents
filtration of incoming water from the mountains and allows more sedimentation to
occur. However, the National Forest lands of the Lake Tahoe Basin, covering more
than two thirds of the basin's watershed, play an important role in assuring
that the beauty of the Lake and the high quality of its water resources are
safeguarded.
| Features |
Metric unit |
English unit |
Maximum depth
(second deepest in the U.S.) |
501 m |
1,645 ft |
| Average depth |
305 m |
1,000 ft |
Maximum diameter
(north-south) |
57 km |
22 mi |
Minimum diameter
(east-west) |
31 km |
12 mi |
| Surface area |
495 km2 |
191 mi2 |
Average surface elevation
(above sea level) |
1,897 m |
6,225 ft |
| Highest peak (Freel Peak) |
3,320 m |
10,891 ft |
Information presented through this site is public domain and derived from
data from the U.S. Geological
Survey. Gossamer Computer Services, LLC is not responsible for the accuracy
of this data.
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