Great Basin National Park

Great Basin National Park

Geology

Rivers and Streams

Ten permanent streams originate in Great Basin National Park between 6,200 and 11,000 ft. (1,890 and 3,353 m) elevation and are fed by numerous springs along their courses. The streams are first and second order headwater streams with an average length of 8 km (5 mi) within the park.

Great Basin's Streams
Six streams (Strawberry, Mill, Lehman, Baker, Snake, and South Fork Big Wash) flow eastward into Snake Valley and the Bonneville Basin. The other four streams (Shingle, Pine, Ridge, and Williams) flow westward into Spring Valley and were originally fishless. Outside park boundaries the majority of these streams are used for irrigation; some water evaporates or percolates into the alluvium before reaching the valley bottom. None of the water flows outside of the Great Basin hydrologic basin.

Stream Life
The variety of habitat types in Snake Range streams supports a diverse spectrum of aquatic insects and invertebrates. Over 100 species of aquatic insects live in the streams. Mayflies, caddisflies, stoneflies, as well as scuds, leeches, and snails are all prominent food sources for resident fish. Bonneville cutthroat trout and three other native fish species are found in park streams, along with some nonnative species.

Seasonal Flow
The amount of water in the creeks varies widely. Baker Creek may only have 1.5 cubic feet per second (cfs) flowing in the winter, but during spring runoff it can exceed 200 cfs. In order to measure the streamflow, Baker and Lehman Creeks have been instrumented with United States Geological Survey (USGS) stream gauges for over 13 years.

Research
Stream gauges were installed by the USGS in 2002 for two years on Strawberry, Snake, South Fork Big Wash, Shingle, Decathon, and Williams Creeks as part of a study to determine the susceptibility of park water resources to groundwater pumping in adjacent valleys (Elliott et al 2006). Gauges are currently being monitored on Lehman Creek by the USGS; and Baker, Rowland, and Snake at the park boundary by park staff. Some of the data can be accessed at: http://waterdata.usgs.gov/nv/nwis.

A number of studies are underway on the streams in the park. These include annual monitoring of fish populations, a baseline water quality inventory, maintaining and operating stream gauges, and periodically monitoring of macroinvertebrates, physical habitat, and riparian vegetation.

Faults

Nevada is one of the most seismically active states in the country, ranking third after California and Alaska. To blame are the state's many faults, found at the base of almost every mountain range. The basin and range topography of the Great Basin is caused by movement along these faults. As these mountain ranges continue to grow through fault-block activity, earthquakes continue to occur. 

What is a Fault?
A fault is simply a fracture in the earth's crust. Movement along faults displace the rock layers on either side. The mountains in much of the Great Basin are large blocks of rock that have been uplifted and tilted by normal activity along fault lines. The basins between the mountains, on the opposite sides of the faults, have slipped downward, and have been filled in and leveled by erosion of the mountains above. Geologists refer to these landforms as "fault-block mountains." 

Earthquake Activity
Most earthquake activity occurs along the eastern Sierra Nevada mountains, on the Nevada's western border. The most powerful earthquake recorded in the state was a 7.6 magnitude quake that occured near Winnemucca in 1915.

While earthquakes don't occur at any regular interval, historically the frequency of an earthquake of magnitude 6 or higher has been one every 10 years, and for magnitude 7 or higher, one every 27 years.

Cave / Karst Systems

Great Basin National Park contains over 40 known caves, filled with unique features.  Some caves contain unique formations such as folia, bulbous stalactites, anthrodites, and shields. Some caves contain features that suggest that deep-seated, hydrothermal waters influenced the caves’ development. The park has high-elevation vertical shafts and horizontal solution caves that have formed along fracture planes. 

Please Note: The only caves in the park open to the public are Lehman Caves, and eight permitted wild caves. All other caves remain closed to protect their fragile ecosystems.

Cave Systems
Four distinctive groups of caves exist in the park. These groups are Lehman Hill Caves, Baker Creek Caves, Snake Creek Caves, and Alpine Caves. Many of the caves within these groups may have formed together either hydrologically and/or structurally.

Lehman Hill Caves
Lehman Caves, Little Muddy Cave, Lehman Annex Cave, and Root Cave make up the Lehman Hill Cave System. The cave passages’ proximity and similar passage orientation supports that these caves may have formed from a single evolving drainage network.

Lehman Annex Cave is the highest in elevation at 7,300 ft. Because of its high elevation, it is thought to have been the first cave to form. Lehman Cave and Root Cave occur at around 7,000 ft.  These two caves probably formed around the same period of time. Little Muddy Cave is at an elevation of 6,800 ft. This cave was discovered because of its spring-like appearance. It may have served as a spring for the system at some point in time. A nearby active spring may be today’s representative of the watercourse that formed Lehman Hill Cave System. The spring is buried in glacial alluvium and shows no external signs of being connected with a karst system.

Baker Creek Caves
In 1958, Arthur Lange investigated the caves of the Baker Creek area for the Western Speleological Institute and concluded that there was once only one system that was cut through the Baker Creek area (Bridgemon 1964). Ice, Crevasse, and Wheelers Deep Caves have been physically connected through cave exploration. Model, Systems Key, and Dynamite Caves have been shown to be connected to Ice-Crevasse-Wheeler Deep hydrologically.

Snake Creek Caves
The Snake Creek cave system includes Snake Creek Cave, Indian Burial Cave, and Fox Skull Cave. 

Snake Creek Cave is the most popular wild cave in Great Basin National Park. The cave is known for its spectacular aragonite anthrodite and frostwork formations. Signatures from Morrison and Roland in 1886 show a long history of the cave’s visitation. The Snake Creek Cave entrance is at an elevation of 6700 ft, and the cave is approximately 1700 ft long.  

Alpine Caves
Alpine caves are caves that occur at high elevation, typically above 9,000ft.  Most of the park's alpine caves can also be considered fracture caves since all initially formed along fracture planes.

High Pit is the highest solution cave found in the park and perhaps the entire state, at an elevation of 11,200 ft. The interesting features of this cave are its high elevation location and the nèvè (compacted, old snow) in its interior. The bottom of High Pit is plugged with snow.  

Long Cold Cave is located at an elevation of about 10,000 ft. The cave is the deepest cave in the park (perhaps in Nevada) at a depth of 480 ft.

Lehman Caves Geology

Water working slowly over the ages is the sculptor of Lehman Caves. The beginning of Lehman Caves can be traced back to approximately 600 million years ago, in the early Cambrian period. Much of what is now Nevada and western Utah was covered by a warm, shallow, inland sea. During this time, many thick layers of sediment accumulated on the sea bottom. Some of the layers were composed of silt, some were sand, and still others were made up of a limy substance that originated from decomposed bodies of minute shell creatures.

One of these limy layers was to become the marble in which Lehman Caves formed. This limy layer was compacted greatly by the weight of latter sediments deposited upon it. Under this pressure, the limy layer slowly turned to limestone rock. Later, as pressure and heat increased, the limestone turned to a low-grade marble. Later, great forces under the earth's crust caused the layers of rock to buckle. This mountain range (the buckle) rose gradually until its peaks were thousands of feet above the valley floor. The rock layers cracked and fractured from the stresses of the uplift. In the future, the pattern of these fractures would help determine the floor plan of the cave.

Acidic ground water came from melting snow and rain. Pure water could not dissolve marble. This water absorbed carbon dioxide from the air and decaying vegetation in the soil, which generated carbonic acid. This weak acid dissolved out cavities in the marble bedrock. Eventually, the water level dropped, leaving air-filled passageways ready for the next stage of cave development.

Seeping water continues to enter the cave at a slow rate. The weak acid dissolves some of the bedrock above the cave and redeposits the mineral (calcite) on the floors, ceilings, and walls of Lehman Caves. Many of the beautiful formations in Lehman Caves are still growing, and are very fragile.

Mountains

The "Great Basin" that Great Basin National Park is named after extends from the Sierra Nevada Range in California to the Wasatch Range in Utah, and from southern Oregon to southern Nevada. This is an area where no water drains to an ocean, but drains inward. As big as it is, the Great Basin is only part of an even larger region called the Basin and Range province that extends down into Mexico. The landscape around Great Basin National Park is a good example of what is found throughout the Basin and Range province - long mountain ranges separated by equally long, flat valleys.

Great Basin National Park encompasses most of the South Snake Range. The bulk of the rocks exposed in this range are formed of sediments like sand, mud and limey ooze (silt and clay particles mixed with calcium carbonate) that were laid down on the bottom of a shallow sea during the late Precambrian and Cambrian (around 560 million years ago).

 

The rocks in the park were further changed during a mountain-building event that occurred around 200 million years ago during the Mesozoic Era. This event, the Sevier Orogeny, pushed layers of rock on top of each other, doubling the thickness of the crust. The layers at the bottom of the stack were metamorphosed slightly - sandstone changed gradually into quartzite, limestone to low-grade marble. Magma rose from deep within the Earth and pushed its way up into these layers. It did not come to the surface, however. Staying underground, it cooled to become granite. Where this hot magma was intruded, the surrounding rock was metamorphosed slightly more.

After all of this activity, the region still did not resemble the present landscape. The modern basins and ranges began to appear only within the last 30 million years or so, during the Cenozoic Era, when the Earth's crust in this area began to stretch in an east-west direction. Bedrock nearest the surface reacted to the crustal stretching by breaking into immense blocks several miles wide, tens of miles long, and thousands of feet thick. Many of these blocks fractured and the pieces tilted and spread out like a row of odd-sized books sliding out of place on a shelf. The remnants of these broken blocks lie beneath the sediment in the basins. Other blocks remained relatively intact and now form the mountain ranges. Because stretching is in an east-west direction, these ranges line up in a north-south direction. The South Snake Range was to see even more change. The younger unmetamorphosed layers of rock on top of the range slid off of the older metamorphosed rocks in a southeasterly direction, on a very low-angle fault line called a decollement. This event makes the South Snake Range a metamorphic core complex. The end of the Cenozoic Era witnessed more granitic intrusions into the park, as well as colder climates that further shaped the landscape.

Alpine glaciers, or cirque glaciers, were present here in the park in several locations along its spine during the Ice Ages. These glaciers carved the peaks to form the cirques like the one underneath Wheeler Peak. Other glacial remnants include terminal and lateral moraines, rocky ridges created at the ice's edge as it pushed its way down the mountain slopes. However, these glaciers did not extend down to the floors of the valleys. Water was collecting in the basins, forming lakes of tremendous size. Lake Bonneville was one of the largest, growing to about the size of today's Lake Michigan. The lakes began to disappear as the last ice age came to a close, but left behind small remnants like the Great Salt Lake and Sevier Lake.

Sevier Lake today is a playa lake, one that collects water in colder and wetter seasons, but dries up in warmer seasons. The evaporating water leaves behind vast stretches of salt flats. Erosion strips down the mountains, and carries sediments down to the valleys creating alluvial fans. These spread out from the canyons down to the valley floors and along with playa lakes, are classic geologic features of basin and range topography. Eventually the sediments are carried to the floor of the valleys, where they have accumulated in layers thousands of feet thick.

The crust beneath the Basin and Range is still stretching today. Faults are active, mountains are pushing upwards, and basins are widening and filling with debris washed down from the high country. This landscape, which appears so everlasting, is actually in the midst of a geologic revolution, played out over millions of years. As the crust continues to stretch, the North American Plate will eventually be divided into two pieces, and a new ocean will form in between them. A future visit to Great Basin National Park might entail an underwater excursion in scuba gear.


Glaciers / Glacial Features

Great Basin National Park is home to the only glacier in Nevada, and one of the southernmost glaciers in the United States. The Wheeler Peak Glacier sits at the base of Wheeler Peak, in a protected cirque around 11,500 feet in elevation. The glacier measures 300 feet long and 400 feet wide. Exact depth is unknown.

What Is a Glacier?

A glacier is a body of ice that lasts from year to year and that flows under its own weight. Glacial ice is made of crushed and recrystallized snowflakes. If the yearly snowfall is greater than yearly melting and evaporation, a glacier will grow. If melting is greater than snowfall, a glacier will shrink.  A crevice that appears each summer near the head of the glacier indicates that the ice is moving.

There are two types of glaciers. Contintental ice sheets cover large areas with ice. Alpine glaciers, like the Wheeler Peak Glacier, are smaller, and found in mountainous terrian. 


A Different Climate

The glacier is a remnant from the past, telling of a much different climate in a region that is now a desert.  The Pleistocene (approx 3 million to 10,000 years ago) was a time of advancing glaciers alternating with warm, dry inter-glacial periods. Continental ice sheets lay to the north of the Great Basin region. Alpine glaciers sculpted some of the mountain ranges within the Great Basin, such as the South Snake Range in Great Basin National Park.

During the last glacial period, glaciers moved down to as low as 9,200 feet.  The climate was an average 8 degrees (F) cooler than today. But climate changes that began with the Holocene period (10,000 years ago) rapidly warmed the region, melting the continental glaciers to the north, and the individual alpine glaciers within the region. The Wheeler Peak Glacier is the last alpine glacier to survive. With continued warming predicted, it is likely the glacier will disappear in as little as 20 years.


Ice Field or Rock Glacier?
The small glacier below Wheeler Peak has been incorrectly called an ice field. According to definition, an ice field is a vast body of ice, the union of several alpine glaciers.  Ice fields are found today in Alaska and British Columbia.

It has correctly been referred to as a rock glacier, however. A rock glacier is a lobe of angular boulders and cobbles that resembles an alpine glacier in outline and in its slow downslope movement. They are found in mountain ranges throughout the world. Inside a rock glacier, ice fills the spaces between the blocks. By freezing, thawing, and sagging, the ice works with gravity to provide the force that moves the rock glacier. 

Viewed from the cliffs above, arc shaped ridges are visible on the surface of the Wheeler Peak Glacier. These ridges are curved because the blocks near the midline of the rock glacier are creeping faster than those on either side.


Visiting the Glacier

The Wheeler Peak Glacier can be seen from several locations in the park.

The Wheeler Peak Overlook on the Wheeler Peak Scenic Drive is the only vantage point from the road. The glacier is seen at the bottom of the sheer rock face of Wheeler Peak.

The Bristlecone/Glacier Trail (4.6 miles roundtrip) will take you to the foot of the glacier. The trailhead for this hike is located at the end of the Wheeler Peak Scenic Drive. The trail begins at an elevation of 9,800 feet and climbs another 1,100 feet. Use caution around the toe of the glacier, as the boulders may not be stable, and small rockslides are common from the cliffs above.

 

Comments

I suppose the glacier below Wheeler Peak is not an ice field but instead is a rock glacier. Still, I had no clue that there are so many glaciers present in America today.