Yosemite Science
As Yosemite National Park celebrates its 125th anniversary, and the National Park Service celebrates its centennial, the U.S. Geological Survey looks back on the integral role its science has played in the long-term health, management, and understanding of the park and its natural resources.
As Yosemite National Park celebrates its 125th anniversary, and the National Park Service celebrates its centennial, the U.S. Geological Survey looks back on the integral role its science has played in the long-term health, management, and understanding of the park and its natural resources.
Historical Topographic and Geologic Mapping
John Muir reported on the existing glaciers of Yosemite as early as 1871, and by 1883, USGS geologists Israel C. Russell, Grove Karl Gilbert, and topographer Willard D. Johnson were formally mapping the glaciers on the highest peaks in Yosemite National Park.
The USGS published its first topographic map of Yosemite in 1897. Compare that early map to the most recent topo map of El Capitan in Yosemite.
The first written geologic observations of Yosemite came from the William Henry Brewer party of 1864. Although it was led by the California Geological Survey, Clarence King was a member of the party and went on to be the first director of the USGS in 1879. Henry W. Turner of the USGS began mapping Yosemite geology in 1897, and was among the first to recognize the differing types of granitic rocks, naming the particular rock of El Capitan, the “El Capitan Granite.”
Turner’s work became the foundation for Frank C. Calkins’ geologic mapping a few years later. Calkins did his geologic field work from 1913 to 1916, but didn’t publish a map during his lifetime. Calkins’ map, Bedrock Geology of the Yosemite Valley Area was eventually published posthumously by his USGS colleagues in 1985, and included a descriptive text. Calkins’ map remains the definitive geologic map of Yosemite Valley.
At the same time Calkins was studying Yosemite’s bedrock, François Matthes was studying the glacial geology of Yosemite. Calkins’ summary of part of Yosemite’s bedrock geology was published in the appendix of Matthes' classic volume, Geologic History of the Yosemite Valley. The pioneering study by Françios Matthes, was published in 1930 as USGS Professional Paper 160.
One of the significant findings to come out of the Matthes volume was the confirmation of the role glaciers played in the shaping of Yosemite Valley. Although proposed much earlier by others, including John Muir, Matthes finally settled the debate of whether glaciers carved the Yosemite Valley we see today.
USGS geologist N. King Huber led the effort in 1985 to publish Calkin’s unfinished map, and in the accompanying text, he describes the origin of Yosemite’s famous “granite” monoliths.
“The rocks that now form the walls and domes of the Yosemite Valley area, part of the lofty Sierra Nevada, originated from molten material (magma) buried miles below the Earth's surface. Cooling and crystallization of this deep-seated magma required millions of years. The resulting rock, composed of interlocking crystals of several kinds of minerals, is called a plutonic rock, named for Pluto, the Roman god of the underworld. Formation of the plutonic rocks of the Sierra occurred over a long timespan, as magma episodically rose from the Earth's interior, intruding older host rocks, and eventually crystallizing to create one of many individual bodies of rock called plutons. Many of these plutons are today exposed at the Earth's surface due to erosion of the once overlying older rocks.”
Long involved with teaching Yosemite geology to park interpretive staff, students, and visitors alike, in 1987, Huber published a non-technical book, USGS Bulletin 1595, The Geologic Story of Yosemite Valley, a “comprehensive geologic view of the natural processes that have created – and are still creating Yosemite.” Later, as a geologist emeritus, Huber published a collection of essays from his years working in the park, as Geological Ramblings in Yosemite.
Rockfall and Debris-flow Hazards
Rockfalls and landslides are natural part of the processes that shape the steep valley walls and rock domes of Yosemite. Most go unnoticed by visitors, but when rockfalls happen in places popular with visitors, the results can be catastrophic. In past years, there have been instances of deaths and injuries in the Park when visitors were hit by rocks falling from the Yosemite Valley walls.
Rockfalls were noticed and written about by visitors and geologists in the late 19th century, but only when a number of significant rockfalls affected lives and Park infrastructure in the 1980s and 1990s, did USGS become involved in formal Yosemite rockfall studies. Pioneered by USGS geologist Gerry Wieczorek, his early ground-breaking reports on rockfall hazards and rockfall potential in Yosemite are the foundation for today’s rockfall studies.
To understand the rockfall process, and to prevent additional deaths or injuries, USGS collaborated with NPS in a landmark study assessing the areas in the Park most at-risk for rockfalls. As a result of the rockfall hazard and risk study that outlined the most hazardous areas, the Park Service removed and repurposed infrastructure located throughout Yosemite Valley including some rental cabins from Curry Village in 2013. When a rock fell on February 11, 2014 and landed within the footprint of one of the cabins that was removed, it demonstrated the merit of the scientific hazard and risk assessment and the prudent removal of buildings by NPS from hazardous areas, and probably saved lives or at least prevented serious injury.
Current USGS research on rockfalls in Yosemite Valley continues, using state-of-the-art lidar and radar technology, as well as motion sensors to track rock movements, as precursors to rockfalls. The U.S. Geological Survey has worked with the National Park Service for three decades, performing timely, relevant rock fall research in and for Yosemite National Park. These efforts include rockfall hazard response and investigation, investigation of triggering mechanisms, compilation of rockfall inventories, and performing rock fall hazard and risk assessments. Taken as a whole, these efforts and body of research has dramatically reduced risks from rock fall in Yosemite.
In addition to investigating the rockfalls in Yosemite, USGS scientists have conducted post-wildfire debris flow assessments in the Park. These debris flows are a particular type of landslide hazard that can occur when heavy rains follow recent wildfires.
USGS maintains long-term forest monitoring plots in Yosemite as part of a larger network of plots that includes Sequoia National Park to the south. In total, the plot network has annually tracked the fates of nearly 30,000 individual trees, including sugar pine, white fir, incense cedar, black oak, ponderosa pine, and red fir, for up to 33 years. USGS researchers use data from the plots to provide the basic information forest managers need to make wise decisions about managing forests in the face of an array of global changes. Discoveries from the plots sometimes lead to expanded studies spanning continents or the globe. For example, USGS researchers noticed that tree death rates had been increasing through time in the forest plots, leading to the broader discovery that tree death rates had doubled across the western United States over the last few decades, a likely consequence of warming. Researchers also noticed that tree mass growth rates increased continuously with tree size in the plots, leading to a global study that overturned the common assumption that tree mass growth eventually declines with size.
Threatened and Endangered Amphibians
USGS biological research in Yosemite National Park is focused on a wide range of sensitive species, ecological process, and land use topics. Sensitive species that are studied include the federally threatened Yosemite toad (Anaxyrus canorus), and the endangered mountain yellow-legged frog (Rana muscosa). Biologists and hydrologists with the USGS monitor other amphibians in Yosemite and other Sierra Nevada sites, including the assessment of pesticides accumulated in Pacific chorus frogs (Pseudacris regilla) and in the environment.
USGS maintains a Yosemite field station where biologists provide credible, timely, and relevant science products to land managers and the broader scientific community. In addition to studies of imperiled amphibians, field station studies include the Sierra Nevada bighorn sheep (Ovis canadensis sierrae) and a host of other alpine mammals. USGS ecological processes studies in Yosemite National Park include those associated with fire regimes, plant invasions, meadow ecosystems, and climate change. These scientific studies inform land-management decisions in Yosemite and elsewhere. Working with other federal agencies, USGS scientists provide a scientific foundation for effective fire management, evaluating the potential environmental effects of pack stock (horses, mules, and/or burros) on Sierra Nevada meadow ecosystems, and the short- and long-term effects of wildfire management on carbon storage in forest ecosystems. USGS also conducts vegetation inventory mapping and rare-plant surveys on behalf of the National park Service.
Happy Isles Streamgage
One hundred years ago, USGS established a streamgage on the Merced River on the Yosemite Valley floor. The Happy Isles streamgage is one of more than 7,000 gages operated and maintained by the USGS in collaboration with other agencies across the country. Here at Happy Isles, Merced River streamflow has been monitored since 1916. This gaging station is part of the National Streamflow Information Program network of the USGS. The historic streamgage station was replaced by a newer station across the Merced River at Happy Isles in 2010.
Streamgage sites provide continuous scientific data such as water level (stage) and flow rate, chemistry, and temperature in the Nation’s rivers. This critical information is used for many purposes, from flood forecasting to recreational planning. Water agencies rely on this information to assess the availability and quality of water supplies. It also helps us understand how streams are affected by human activities and by climate change.
Measurements from Happy Isles and other USGS streamgaging stations are used by the National Weather Service to issue flood warnings and water-supply forecasts. In addition to flood forecasting, the streamgage data are used for water allocations and reservoir releases. With the information gages provide, along with newer weather forecasting techniques, reservoir releases in California are being adjusted to save water during the drought.
The Happy Isles streamgage is known as a “benchmark” streamgage, because no human development exists upstream of the gage. Benchmark streamgages provide a baseline for understanding human impacts on rivers and streams.
Water plays a central role in global climate-change research, and hydrologic processes are leading indicators because they are easily measured and respond quickly to environmental change. USGS streamflow measurements, especially those from benchmark gages, provide an invaluable foundation for studying the effects of climate change because of their accuracy and long duration. Studying seasonal streamflow changes may help us understand and respond to likely future Sierra Nevada climatic patterns of less snow and more rain in the winter, a shift that could affect everything from California’s water supplies, to ecosystem health, to flood risks.
The U.S. Geological Survey has had a long and fruitful relationship with the National Park Service, meeting their needs for science, and we hope it continues for another 100 years. Congratulations to NPS on the occasion of their Centennial Celebration.
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