AGU was founded in 1919, making this coming year its 100th anniversary. In honor of this milestone, we’d like to take some time to reflect on the work of the great minds that have laid the foundations for geoscience as we know it today. Science is an iterative discipline, and each discovery is built on the solid work of those who’ve come before.
Grove Karl Gilbert was an explorer, a geographer, and a geologist whose 75-year-long life spanned an age of heroic geology. It is no wonder that his contributions are broadly celebrated. The number of problems he tackled over 50 years was great, and the style with which he approached each problem has been continuously emulated in the century since his passing. As a leader, he helped to launch the U.S. Geological Survey (USGS) and was its chief geologist under the renowned explorer and second USGS director John Wesley Powell.
Gilbert was a founding member of the National Geographic Society. He was twice the president of the Geological Society of America. Today, we vie for a snippet of his coattails, naming awards and fellowships in his honor.
Driven Explorer and Gentle ColleagueGilbert had a knack for harnessing the geography of the land in the cause of something greater: extraction of knowledge about the processes at work.In the field, Gilbert thrived. He drew, measured, and (in fervent discussion with his fellow field researchers) devised explanations for the spectacular landscapes that they beheld across the American West. The West was filled with world-class natural experiments to exploit. From the dry lake bed of the Bonneville basin to the few laccolithic mountains that interrupt the stair-step topography of the Colorado Plateau, Gilbert had a knack for harnessing the geography of the land in the cause of something greater: extraction of knowledge about the processes at work.
He also had a knack for conducting himself in his work and his life in ways that remain a model for geoscientists even to this day. William Morris Davis [Davis, 1927] spends as much of the foreword in his biography of Gilbert alerting the reader to the qualities of the man as he does summarizing why his science will survive. Gilbert was honest and honorable. He developed deep and abiding friendships. He was evenhanded. He did not seek leadership but rather accepted it when it came his way. The closing words of that foreword bear repeating: “His career covers a remarkable epoch in American science, and it is a great credit to American science that it should have given high rank to a man of his gentle personality” (p. 1).
First ExposureThe very aridity of the West that posed challenges to its settlement was a boon to the geologist; beyond the hundredth meridian running through the middle of the Great Plains, the vistas were long, and the rocks were ready to be read.Gilbert’s first exposure to the American West came through participation in the Wheeler Survey, one of the four great surveys of the American West (headed by George Wheeler, Clarence King, Ferdinand Vandeveer Hayden, and Powell [see Goetzmann, 1966; Pyne, 1980]). In a marathon summer of 1871, Gilbert saw more than 1,500 kilometers of what we now call the Basin and Range Province, covering parts of what are now the states of California, Nevada, Utah, and Arizona. The very aridity of the West that posed challenges to its settlement was a boon to the geologist; beyond the hundredth meridian running through the middle of the Great Plains, the vistas were long, and the rocks were ready to be read, without the vegetative cloak of the east and of the old world [Stegner, 1954].
Gilbert and his fellow scientists and topographers worked in small teams from spring to autumn, exploiting the newly completed transcontinental railroad. His colleague Clarence Edward Dutton described the comradery shared by the special team of Dutton, an outstanding explorer and geologist in his own right [Anderson, 2017], Powell, and Gilbert as “a bond of affection and mutual confidence which made the study in a peculiar sense a labor of love.” Among these remarkable explorers, “this geological wonderland was the never-ending theme of discussion,” Dutton recalled, “and ideas were interchanged, amplified, and developed by mutual criticism and suggestion” [Anderson, 2017, pp. 41–42].
A Career in Two PartsThe arc of Gilbert’s career may be broken into two segments. In the first, he was tied closely to Powell, the head of USGS from 1881 to 1894. It is in these years that Gilbert crafted his monumental works on the Henry Mountains and Lake Bonneville [Gilbert, 1890]. Powell’s [1878] Report on the Lands of the Arid Region, on which both Gilbert and Dutton played key roles, argued that rational settlement of the West must occur around its water. This effort to guide western development scientifically ultimately failed against political pressures, and Powell was forced from office [see Stegner, 1954].On the 1899 Harriman Expedition to Alaska, Gilbert rubbed shoulders with the best botanists, zoologists, geologists, artists, photographers, and writers of the age.
In the second part of his career, following the death of his wife after a long illness, Gilbert was rejuvenated by participation in the 1899 Harriman Expedition to Alaska, aboard Edward Harriman’s steamship SS Elder [Goetzmann and Sloan, 1982]. There, Gilbert rubbed shoulders with the best botanists, zoologists, geologists, artists, photographers, and writers of the age. The expedition spent months plying Alaska’s coasts, landing parties ashore to study wildlife, geology, and the landscape. Explorations of Glacier Bay and College Fjord inspired Gilbert’s contribution, titled Glaciers and Glaciation [Gilbert, 1899], to the five-volume set published at the end of the voyage. Upon return, Gilbert began splitting his time between Washington, D. C., and California, where he continued his study of glacially carved landscapes in the Sierras. He was also positioned to evaluate the aftermath of the 1906 San Francisco earthquake [Gilbert et al., 1907] and to address the environmental impact of hydraulically mined gold-bearing gravels of the eastern Sierras.
The GKG LegacyGilbert’s work has stood the test of time. In every class I teach, I trot out his 1909 piece on the convexity of hilltops [Gilbert, 1909], the simplest, most elegant explanation of why a steady-state hilltop ought to be smooth, like an inverted parabola. His work stands the test of time because it exposes the fundamental, immutable physics of the problem and because it is honest. He always pointed out not only the strengths but the weaknesses of his arguments [Baker, 2015].
The Henry Mountains
Fig. 1. This south-looking view of the Henry Mountains from the rim of South Caineville Plateau, Utah, highlights their splendid isolation. In the foreground, the sandstones and shales of the Mesozoic section are flat lying, carved into the steplike forms that characterize the Colorado Plateau. This pattern is interrupted by Tertiary igneous intrusions that have warped the Mesozoic section to create the isolated blisters of the Henry Mountains that Gilbert targets in his 1877 monograph (see Figure 2). Credit: R. S. Anderson
In his 1877 Henry Mountains report, his first big assignment under Powell, Gilbert extolls the virtues of that range of half a dozen isolated peaks embedded in the layered Mesozoic rocks of the Colorado Plateau [Gilbert, 1877] (Figures 1 and 2). Gilbert could clearly see both how the intrusion of magma has bowed the strata and how erosion has sculpted the rock to reveal these igneous roots. In chapter 5, titled “Landscape Sculpture,” Gilbert essentially defines modern geomorphology by describing first the processes of erosion and then what governs their efficiency. Rock must first be weathered to be freed from neighboring rock. Emancipated particles are then transported down slopes by running water and into channels. There, they are further transported by deeper flowing water. In the streams, the finer particles are transported in suspension, and the coarser particles are transported as bed load. As they bounce and bash downstream, the particles both erode the bed and are themselves further broken down. This conveyor belt system of hillslopes feeding channels is precisely how we now view landscapes, and the processes Gilbert enumerated are those we still study.
Fig. 2. Frontispiece of the Report on the Geology of the Henry Mountains. Its caption reads, “Half-stereogram of Mount Ellsworth, drawn to illustrate the form of the displacement and the progress of erosion. The base of the figure represents the sea-level. The remote half shows the result of uplift alone; the near half, the result of uplift and erosion or the actual condition.” This description serves to advertise the main themes of the work but also suggests the artful care with which this and many of the reports at the time were produced. Credit: U.S. Geological Survey, Department of the Interior/USGS Lake Bonneville 
Fig. 3. Plate 50 of the Bonneville report (see p. 374). The lake occupied a 250-km swath of the eastern half of the Great Basin. The complexity of the map pattern reflects the fact that many ranges of the Basin and Range Province became islands in the lake (denoted as north–south elongated white patches with surrounding lines depicting the presence of water). Titled “theoretic curves of the post-Bonneville deformation,” the smooth lines with numbers on the map, illustrate Gilbert’s interpolation and extrapolation of the measured elevations of the Bonneville shoreline (the highest in the basin) that he had mapped around each of the islands. Elevations are given in feet above sea level. A few of the measured elevations are noted. Contours of these shoreline elevations, given at 50-foot (~15-meter) intervals, reveal that the middle of the basin had rebounded by 150 feet (~50 meters) more than the edges of the basin in response to the removal of the lake load. Credit: U.S. Geological Survey, Department of the Interior/USGS
Gilbert’s work on Lake Bonneville revealed that our planet’s interior behaves as if it were a fluid, deforming as long-wavelength loads of water, rock, and ice are moved about on the surface [Gilbert, 1890]. In the eastern Great Basin, the wetter, cooler climate of the last glacial cycle allowed Lake Bonneville’s waters to reach their highest levels and enabled the development of extensive beaches and deltas more than 100 meters above the ancient lake’s modern remnant, the Great Salt Lake. But what made this particular natural experiment both unique and more useful was that the 250-kilometer-wide lake occupied a terrain that had been rifted apart to produce the Basin and Range Province. Each range poked out of the lake as an island, each island ringed with the same identifiable sequence of ancient shorelines. Gilbert rode his horse along these shorelines, documenting their elevation with a barometer. The resulting map (Figure 3) revealed that those shorelines that bound mountain ranges in the middle of the basin were significantly higher than those around the edges. Gilbert suggested that this rock uplift resulted from rebound of the basin due to the removal of the water load as the lake first catastrophically dropped 100 meters in a flood (now known as the Bonneville flood; see Abril-Hernández et al. [2018]) and then more slowly lost volume in a warming climate to evaporation to become the present Great Salt Lake. This demanded a fluidlike behavior of the planet’s interior; mantle was first pushed away from the load as the lake grew and then flowed back under the basin as most of the lake vanished. These and other shorelines around other lakes around the planet still serve as some of the best probes of the viscosity structure of the mantle [e.g., Bills et al., 1994].
Sediment Transport and Hydraulic MiningGilbert’s 1914 U.S. Geological Survey Professional Paper titled “The Transportation of Débris by Running Water” laid the foundation for all future sediment transport studies.Gilbert also focused on the consequence of large-scale human disturbance of a river system. Hydraulic mining on the Yuba River tributaries lasted from 1855 to 1884 before a court order shut down the practice. The millions of tons of sediment washed from the hillslopes by high-powered hoses were transported to the rivers, where their slow downstream motion then caused aggradation of floodplains. The continued motion of this slug of sediment, what we would now call “legacy sediment” [e.g., James et al., 2017, pp. 4, 10, 11, 16], constituted a huge, although unintended, experiment. On the one hand, Gilbert sought to exploit the experiment for insight about how a landscape responds to a major perturbation, and on the other hand, he wished to illuminate, for the public, the results of poor mining and land use practices. Gilbert built flumes on the grounds of the University of California, Berkeley, campus and ran an extensive matrix of experiments to explore the roles of grain size and water discharge. At the age of 71, his exposition of these experiments in his U.S. Geological Survey Professional Paper titled “The Transportation of Débris by Running Water” [Gilbert, 1914] laid the foundation for all future sediment transport studies.
He then turned to his treatise on hydraulic mining, published just a year before his death at age 75 [Gilbert, 1917]. This paper stands out as a forerunner of environmental impact statements and as a work ultimately motivated by the desire to discover the complexity of the natural world and how human modification of one element of it may propagate through the system.
All of these works have served as the foundations for research in a variety of Earth science subdisciplines. From beaches to waterfalls, from glacial striae to deformed lake basins, Gilbert focused on the processes responsible for landscapes and their evolution at all scales. His persistent message about the linkages in landscapes pushed the community toward a whole-Earth perspective that is all the more important on this rapidly changing planet.
The Century AfterOne hundred years have passed since Grove Karl Gilbert’s final days. AGU has recently announced that in 2019, the scientific society will celebrate the Centennial of its founding in 1919, the year after Gilbert’s passing, with extensive coverage on Eos.org and elsewhere of the past century’s advances and transformations in Earth and space science.
We may have new tools, but Gilbert clearly organized how the elements of the landscape link and compactly laid out the physics and chemistry of many problems on which we still labor.Among the stories will surely be that of geoscientists learning to use cosmogenic nuclides as clocks in the landscape, making precision dating of landforms and measurements of rates of geological processes possible that were undreamed of in Gilbert’s day. AGU’s upcoming retrospective will also note the advent of light detection and ranging (lidar) sensors and photogrammetry, as well as digital elevation models that are built from lidar data and have replaced Gilbert’s stunning sketches of the land [see Hunt, 1988].
Although scientific instruments and institutions have changed dramatically since Gilbert’s time, we are, in many ways, still pursuing questions for which he helped create the foundations of our understanding in his pioneering work, for example, the question of what controls the rates of surface processes. We may have new tools, but Gilbert clearly organized how the elements of the landscape link and compactly laid out the physics and chemistry of many problems on which we still labor.
At this time of unprecedented disregard for science, truth, and civility in public discourse, the record of Gilbert’s life and work remains a touchstone for modern geoscientists. We should do science as Gilbert did. And we should behave as scientists and as citizens of the planet as Gilbert did.
AcknowledgmentsI appreciate careful reading of an earlier version of this article by S. P. Anderson and Rachel Glade and of the present version by Andrew Wilcox and an anonymous reviewer.
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