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February 14, 2022

High-resolution topographic data reveal new faults, landslides, hydrothermal systems, and volcanic features never documented before.  Able to see through vegetation, lidar maps the bare earth, unveiling the impact of past events and current processes that shape Yellowstone National Park.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Dr. Ben Crosby, Professor, and Kyra Bornong, graduate student, with the Department of Geosciences at Idaho State University.

Photo and lidar image of Silver Gate landslide, Yellowstone National Park
Top image is a view of the Silver Gate landslide complex, near Mammoth Hot Springs, from Bunsen Peak. Bottom shows roughly the same view using lidar data, colored to show elevation highs and lows and shaded by slope. Landslide scarps, roads, trails, and Glen Creek (lower left), all obscured by trees in the photograph, are much more visible in the lidar. (Photo by Michael Poland, lidar data from USGS 3DEP over slope map visualized in ArcGIS Pro.)

The topographic texture of the earth’s surface tells a story.  From afar, we see ridges and valleys, shaped over thousands of years, sculpted by rivers and glaciers.  Zooming into an individual hillside or a stretch of river bottom, subtle bumps and breaks in the land’s surface reveal the imprint of past events, such as floods or landslides.  The scale at which geologists observe landscapes influences the stories they tell about them.  

Previous generations of scientists interpreted Yellowstone’s landscape using aerial photos or through fieldwork; both techniques are complicated by the presence of dense vegetation.  An unprecedented, high-resolution lidar topographic dataset released in February 2022 changes all that.  Lidar stands for “Light Detection and Ranging” and is a method that uses a laser to determine distances between a source and target with very high precision.  When a lidar system is mounted on an airplane, it allows for high-resolution mapping of topography and can even effectively “see” through vegetation.  In the same way that the invention of the microscope enabled biologists to visualize the inner workings of cells, lidar offers geoscientists access to the subtle and often obscured textures of the earth’s surface.     

In the fall of 2020, a small plane flew 436 overlapping swaths of lidar data over Yellowstone National Park, systematically traversing the area like a lawnmower. Pulsing out the belly of the plane, a downturned laser swept side-to-side, precisely measuring the elevation of the bare earth below.  After 16 months of processing, the data were released to the public.  Over 290 billion individual measurements resolve the park’s topography at a resolution of slightly less than one measurement every square foot and capable of detecting elevation differences of just a few inches.  This just-about enables you to resolve individual bison grazing in Lamar Valley or measure the height of Old Faithful’s sinter cone!

For geologists and geomorphologists who study the shape of landscapes, lidar data not only reveal the presence of unmapped features of the landscape, but also allow measurement of the size and character of these features. For example, in the late 1960s and early 1970s, USGS geologists Richmond, Pierce, and Waldrop spent almost a decade mapping, by hand, the surficial geology of Yellowstone, recognizing the signature of glaciers, patterns in river and lake systems, and the origins of many cryptic landforms. They laid the foundation for future analysis but were limited by the tools available to make their observations.  

Photo and lidar image of Highway 191 landslide, near Yellowstone National Park
Top shows aerial photo of a section of US Highway 191 north of West Yellowstone in Montana. Bottom shows lidar imagery that reveals the road traversing a landslide deposit. High elevations are brown and white, and green is lower elevation. Shading indicates steeper slopes. A highly trained eye might be able to identify the landslide from the aerial photo, but it is more obvious in the lidar. Without vegetation, the boundaries and internal features of the landslide are clear. One can readily interpret its movement type and age relative to nearby features, like the highway built over it. Though subtle, an unmapped west-northwest trending, down-to-the-south fault is observed on both sides of the highway and crosses the south side of the landslide, revealing that slip occurred on the fault after the landslide formed.  (Photo from ESRI aerial imagery, lidar from USGS 3DEP over slope map visualized in ArcGIS Pro.)

In their studies, the geologists mapped hundreds of landslide deposits across the park, like Silver Gate, near Mammoth Hot Springs.  In the lidar, however, the high-resolution topography reveals thousands of landslides of varying sizes.  We can also see young faults crisscrossing the park, leaving linear steps in the topography.  The lidar reveals numerous locations where previously mapped faults have no surface expression (a false positive?) and other locations where no fault is mapped yet a clear break in topography suggests one (a false negative?).  The new data offer an opportunity to revisit and revise our interpretation of the park’s surface geology, adding more detail to what is already known.  

Further, these data enable new lines of investigation that arise from creative exploration of the lidar.  Can variations in lake shorelines reveal past tsunamis?  Can clusters of landslides indicate extreme weather events?  Can the distribution of waterfalls explain the rates of tectonic activity? 

Beyond revelations about the more distant past, the 2020 park-wide dataset offers a baseline with which to compare past and future lidar acquisitions. Change detection is possible using numerous local datasets collected between 2007 and the present.  Plenty of additional data will be acquired in the future.  Rivers migrate, landslides creep, and the ground deforms.  What will these changes reveal?   It is too early to tell exactly what insights future scientists will extract from the lidar data, but it is certain that the new work will deepen our understanding, curiosity, and excitement for this dynamic landscape.

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