Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Professor Ben Crosby and graduate student Kyra Bornong from the Department of Geosciences at Idaho State University.
The topographic texture of the earth’s surface tells a story. From afar, you can see ridges and valleys shaped over thousands of years, sculpted by rivers and glaciers. Zooming in on an individual hill or part of a river bottom, subtle bumps and breaks in the surface of the terrain 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 have interpreted the Yellowstone 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 a target with very high precision. When a LiDAR system is mounted on an aircraft, 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 allowed biologists to visualize the inner workings of cells, LiDAR offers geoscientists access to the subtle and often obscured textures of the earth’s surface.
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In the fall of 2020, a small plane flew over 436 overlapping bands of LiDAR data over Yellowstone National Park, systematically traversing the area like a lawnmower. Pulsating over the plane’s belly, a downward-pointing laser swept from side to side, accurately measuring the elevation of the bare land below. After 16 months of processing, the data was made public. More than 290 billion individual measurements resolve the topography of the park to a resolution of just under one measurement per square foot and capable of detecting elevation differences of only a few centimeters. This pretty much lets you solve 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 reveals the presence of unmapped features of the landscape, but also allows the size and character of those features to be measured. For example, in the late 1960s and early 1970s, USGS geologists Richmond, Pierce, and Waldrop spent nearly a decade hand-mapping the surficial geology of Yellowstone, recognizing the signature of glaciers, patterns of river and lake systems, and the origins of many cryptic landforms. They laid the groundwork for future analysis, but were limited by the tools available to make their observations.
In their studies, geologists mapped hundreds of landslide deposits across the park, such as Silver Gate near Mammoth Hot Springs. In LiDAR, however, high-resolution topography reveals thousands of landslides of varying sizes. Young faults can also be seen crisscrossing the park, leaving linear steps in the topography. LiDAR reveals many locations where previously mapped faults have no surface expression (a false positive?) and other locations where no faults are mapped, but a clear break in the topography suggests one ( a false negative?). The new data provide an opportunity to revisit and revise our interpretation of the park’s surficial geology, adding more detail to what is already known.
Moreover, these data allow new avenues of investigation that arise from the creative exploration of LiDAR. Can lakeshore variations reveal past tsunamis? Can groups of landslides indicate extreme weather events? Can the distribution of waterfalls explain rates of tectonic activity?
Beyond revelations about the more distant past, the 2020 park-wide dataset provides a baseline against which to compare past and future LiDAR acquisitions. Change detection is possible using many local datasets collected between 2007 and present. Much more data will be acquired in the future. Rivers migrate, landslides creep in and the ground deforms. What will these changes reveal? It’s too early to tell exactly what insights future scientists will gain from LiDAR data, but the new work is sure to deepen our understanding, curiosity and excitement about this dynamic landscape.