Geomorphology, the study of landforms and the processes that shape them, emerged in its modern form in the mid-twentieth century and continues to change. Its practice, however, derives from the convergence of discrete foundations in the Earth, water and applied sciences over the past 400 years, underpinned by advances in analysis and technology. The Earth-science foundation was built as early geologists sought to explain landforms as expressions of underlying rocks or as surrogates for vanished stratigraphies. This approach, more speculative than definitive, rarely explained the processes at work. The water and applied sciences were more discerning but only slowly came to be integrated into morphodynamic explanations. All three foundations, initially vague on time and space, emerged during the Scientific Revolution of the seventeenth century and were refined during the agrarian and industrial revolutions of the eighteenth and nineteenth centuries, before converging into modern practice during the electronic age of the twentieth century.

A prominent physical geographer offers a brief primer on climate change in general and then brings spatial and temporal perspectives to bear in an assessment of the past, present, and future changes of climate over Eurasia. More specifically, he addresses climate change and feedbacks for Eurasia over longer (tectonic forcing, >10(5) years), intermediate (Earth's orbital relations, 10(4)-10(5) years), and shorter timeframes (<10(4) years), emphasizing that climates change more or less continuously in response to many forcing factors (solar output, Earth's eccentric orbit, rotational tilt, precession, and interactive atmosphere-ocean-land systems, including human impacts). Although these factors operate at different rates and timescales, they may coincide at times to promote rapid change. The nesting of the current, three-decade pattern of warming within longer centennial- and millennial-scale cycles of warming and cooling since the Holocene Optimum (itself a warm interglacial stage within warm and cold cycles in the late Cenozoic over the last 50 million years) shows that the recent rapid warming since 1980 is not unique in Earth history, although it does warrant concern and raises questions of global significance. Journal of Economic Literature.

Owens Lake has existed for most of the past 800,000 yr, but the sequence of interconnected lakes and streams of which it was often part, the Owens River cascade, last flourished during late Pleistocene time. A fluctuating, increasingly saline, terminal lake survived into the late Holocene until upstream water diversions to the Los Angeles Aqueduct began in 1913. Shoreline fragments and beach stratigraphy indicate that the lake reached its highest late Pleistocene level around 23.5 ka, during the Last Glacial Maximum, when it was fed by meltwaters from Sierra Nevada glaciers and spilled southward to Searles Lake and beyond. The lake then fell to relatively low levels after 16.5 ka before experiencing terminal Pleistocene oscillations related to hydroclimatic forcing, which involved changing regional precipitation regimes rather than major inputs from Sierra Nevada glaciers. Two major transgressions occurred. The first culminated around 14.3 ka and was probably related to a cooler, wetter regional climate. The second culminated around 12.8 ka and was linked to the earlier wetter phase of the Younger Dryas cold event. However, the high late Pleistocene shoreline is deformed, and the highest beach ranges in elevation from 1140 m to 1167 m above sea level. If the terminal Pleistocene lake overflowed, as suggested here, then its outlet has also been raised since 12.8 ka. This deformation appears to have involved uplift of the Coso Range magmatic complex relative to subsidence and faulting within the Owens Lake graben between the Sierra Nevada and Inyo Mountains frontal faults. Such deformation confounds simple hydroclimatic explanations of lake behavior and must be incorporated into models that seek to interpret the changing form and geochemistry of Owens Lake and the frequency of its spillage southward to Searles Lake.

Lakes in one form or another have characterized the western Mojave Desert since at least Miocene time. The most recent of these, Lake Thompson, developed in the late Pleistocene, when it covered as much as 950 km2 and rose to at least 710 m above sea level. During Holocene time, the lake desiccated, and is now represented by Rogers, Rosamond, and Buckhorn dry lakes, which may flood up to 200 km2 during unusually wet phases. The spatial dimensions of the former lake are defined by modest geomorphic and lithostratigraphic units, mostly exposed lake beds and beach ridges interbedded with and later mantled by fluvial and eolian deposits. The lake's temporal devolution is revealed by four cores, and ages are constrained by accelerator mass spectrometry 14C dating of organic sediment. These cores show a deep perennial lake from before 36 ka to at least 34 ka, a shallow but variable perennial lake from before 26 ka to 21 ka, followed by lowering and at least partial exposure of the lake floor to deflation and alluviation. A shallow perennial lake returned during the terminal Pleistocene, from around 16.2 ka to at least 12.6 ka, forming distinctive beach ridges beyond the margins of the present dry lakes, and it may have reappeared in the early Holocene. During subsequent Holocene desiccation, lake segmentation occurred as waves and currents generated lower sequences of beach ridges around contracting lakes. These ridges became mantled with eolian sand, but, as fluvial sediment inputs diminished with increasing aridity, these dunes were degraded, and their roots survive today as indurated yardangs.

Abstract Scientific investigations of Pleistocene pluvial lakes in the American West occurred in five phases. The pioneer phase prior to 1870 saw former lakes identified by missionary priests, fur trappers, military expeditions and railroad surveyors. The classic phase, between 1870 and 1920, linked initially with independent surveys and, after 1879, with the United States Geological Survey and with irrigation and mining ventures, saw most lakes identified and described by such worthies as Gilbert, Russell, Gale, Waring and Thompson. A consolidation phase from 1920 to 1955 provided synthesis and new data but, in the absence of age controls, saw much speculation about temporal links between pluvial lakes, glacial stages, and climate forcing. The initial dating phase between 1955 and 1980 saw radiocarbon dating applied to late Pleistocene lakes and their Holocene relics and successors. The integrative phase since 1980, supported by enhanced field, remote sensing, laboratory and dating techniques, has seen an array of issues involving pluvial lakes linked to changes in regional ecology and global climate. In the above sequence, progress from one phase to the next reflected changes in the intellectual climate and advances in scientific methods. Today, we reflect on the episodic but cumulative increase in knowledge about late Pleistocene pluvial lakes, especially for Lake Bonneville, Lake Lahontan and the eastern California lake cascade. The record of earlier Pleistocene lakes, in some cases successors to Miocene and Pliocene lakes, is less certain because of deformation and erosion or burial. Continuing challenges involve evaluation of the Pleistocene lake record as a whole in the context of late Cenozoic tectonic and climate change, and of contemporary environmental and water-resource issues.

Sediment records from two lakes in the east-central Sierra Nevada, California, provide evidence of cooling and hydrological shifts during the Younger Dryas stade (YD; similar to 12,900-11,500 cal yr BP). A chironomid transfer function suggests that lake-water temperatures were depressed by 2 degrees C to 4 degrees C relative to maximum temperatures during the preceding Bolling-Allerod interstade (BA; similar to 14,500-12,900 cal yr BP). Diatom and stable isotope records suggest dry conditions during the latter part of the BA interstade and development of relatively moist conditions during the initiation of the YID stade, with a reversion to drier conditions later in the YD. These paleohydrological inferences correlate with similar timed changes detected in the adjacent Great Basin. Vegetation response during the YD stade includes the development of more open and xeric vegetation toward the end of the YD. The new records support linkages between the North Atlantic, the North Pacific, and widespread YD cooling in western North America, but they also suggest complex hydrological influences. Shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the YD stade in the Sierra Nevada and the discordance in some paleohydrological and glacial records of the YD stade from the western United States. (C) 2008 University of Washington. All rights reserved.

"Physical Geography in a Rapidly Changing World: An Editorial." Physical Geography, 28(1), p. iii

Clarence Edward Dutton (1841-1912) was one of several scientists who laid the foundations for modern geology from their work in North America during the late nineteenth century. Dutton was a career soldier who fought in the American Civil War and remained with the US Army Ordnance Corps to his retirement in 1901. Despite military obligations, Dutton developed a profound interest in geology and, on secondment first to the Powell Survey and later to the fledgling US Geological Survey, made important contributions to volcanic geology, seismology and physical geology. His lifelong fascination with volcanism led to improved understanding of the volcanic geology of the American West, Hawaii, and Central America. This work linked naturally with the emerging science of seismology, as reflected in his study of the 1886 earthquake in Charleston, South Carolina, and he is often credited with introducing the 'new seismology' to American scientific audiences. Awareness of volcanic and seismic hazards in turn led him to caution against a proposed sea-level canal across the Nicaraguan isthmus. His contributions to physical geology are most evident in several reports on the American West, notably the Report on the Geology of the High Plateaus of Utah (1880), the Tertiary History of the Grand Canon District (1882), and Mount Taylor and the Zuni Plateau (1885). These reports, presented in colourful prose, reveal both the author's scientific acumen and his aesthetic appreciation of nature.Whereas most of Dutton's work must now be placed in its historical context, in his recognition of isostasy, a term he coined in 1882 to reflect the debate then raging concerning Earth's crustal behaviour, his ideas were remarkably prescient. Dutton's interest in isostasy derived in part from his studies of volcanic geology, seismology, and crustal behaviour, and in part from his fieldwork in the American West. Initially, however, it was Dutton's description of the great denudation of the Colorado Plateau, rather than any isostatic implications, that influenced geomorphology during the earlier twentienth century, dominated as it was by Davis' cycle of erosion. The subsequent demise of Davisian geomorphology, and the ensuing quest for alternative models, led to a reawakening of interest in isostasy as a concept basic to the explanation of Earth's surface features. Somewhat belatedly, Dutton's concept of isostasy is once again at the centre of debate regarding denudation and crustal behaviour. Wherever these debates focus, they confront a problem fundamental to geology, geodesy and geophysics, namely the extent to which the Earth's present relief reflects a quest for balance between the subsurface forces generating uplift, subsidence and mass transfers at depth, and the climate-induced processes responsible for denudation and mass transfers of rock waste across the surface. Dutton's probing of isostasy predated modern debate in geomorphology by more than a century.

Tectonism is the science of Earth movements and the rocks and structures involved therein. These movements build the structural framework that supports the stage on which surface processes, plants, animals and, most recently, people pursue their various roles under an atmospheric canopy. An appreciation of this tectonic framework is thus a desirable starting point for understanding the physical geography of South America, from its roots in the distant past through the many and varied changes that have shaped the landscapes visible today. Tectonic science recognizes that Earth’s lithosphere comprises rocks of varying density that mobilize as relatively rigid plates, some continental in origin, some oceanic, and some, like the South American plate, amalgams of both continental and oceanic rocks. These plates shift in response to deep-seated forces, such as convection in the upper mantle, and crustal forces involving push and pull mechanics between plates. Crustal motions, augmented by magmatism, erosion, and deposition, in turn generate complex three-dimensional patterns. Although plate architecture has changed over geologic time, Earth’s lithosphere is presently organized into seven major plates, including the South American plate, and numerous smaller plates and slivers. The crustal mobility implicit in plate tectonics often focuses more attention on plate margins than on plate interiors. In this respect, it is usual to distinguish between passive margins, where plates are rifting and diverging, and active margins, where plates are either converging or shearing laterally alongside one another. At passive or divergent margins, such as the present eastern margin of the South American plate, severe crustal deformation is rare but crustal flexuring (epeirogeny), faulting, and volcanism occur as plates shift away from spreading centers, such as the Mid-Atlantic Ridge, where new crust is forming. Despite this lack of severe postrift deformation, however, passive margins commonly involve the separation of highly deformed rocks and structures that were involved in the earlier assembly of continental plates, as shown by similar structural legacies in the facing continental margins of eastern South America and western Africa. At active convergent margins, mountain building (orogeny) commonly results from subduction of oceanic plates, collision of continental plates, or accretion of displaced terranes.

The Cycle of Erosion formulated by the American geographer William Morris Davis in the 1880s remained the dominant paradigm in geomorphology well into the 20th century, before it waned in response to improved understanding of Earth's crustal and surface behavior. The Davisian model sought to explain landforms in terms of structure, process, and stage. Following initial rapid tectonic uplift, landforms were presumed to evolve on a quiescent crust through stages of youth, maturity, and old age, to culminate in a peneplain. A new cycle would be initiated by landform rejuvenation in response to a changing base level of erosion. This model was a reflection of its time, of the cycle mania of the 19th century, which in turn was founded on Hutton's limitless "succession of worlds" and dissatisfaction with earlier notions of landscape origins constrained by limited Earth time. Davis's model was derived from ideas regarding orogenic cycles favored by Dana and Le Conte, and of prolonged subaerial denudation toward base-level observed by Powell and Dutton. The model's supremacy was challenged from time to time, notably by the Pencks (father and son) and by alternative cyclic denudation models that invoked pediplanation and etchplanation rather than peneplanation. The relevance of the Davisian model declined after 1940 in response to a growing awareness of Earth's crustal mobility, changing climates and geomorphic processes, and refined dating of geologic time. The subsequent quantitative revolution in geomorphology, with its emphasis on measurement of form and process aided by rapidly improving technologies, and based in part on lingering antecedents, sounded the death knell for the Davisian model but also triggered something of a theoretical hiatus. In recent years, resurrection of the concept of isostasy, defined by Dutton but ignored by Davis, has led to the formulation of a more realistic but more complex model, briefly introduced here, in which landforms may be viewed as responses to more-or-less continuous interaction between tectonic activity, subaerial denudation, and isostatic adjustment.

Earth’s physical landscapes are framed initially by tectonism, reshaped by climate, garnished by plants and animals, and modified by human activity. Tectonism constructs the physical framework of the continents and ocean floors. Climate, the synthesis of weather, generates the surface processes that reshape this framework through erosion and sedimentation, and also provides the conditions necessary to support life. In various guises, tectonism and climate have played these roles from early in Earth history, although 90% of Earth time had passed before the continents began to acquire vascular plants and land animals. However, because Earth’s crust is ponderously mobile and climate depends ultimately on the variable receipt of solar radiation, tectonic and climatic forcing vary across time and space. Consequently, continents come to acquire distinctive suites of landscapes that reflect changing locational, tectonic, climatic, and biotic influences over time. South America exemplifies this concept—a continent whose distinctive qualities owe much to the roles played by tectonism and climate over time, including their impacts on landforms and biota. Tectonism and climate are interactive forces. By determining the distribution and shape of land masses and ocean basins, tectonism influences the relative importance of continentality and oceanicity to climate. Over time, tectonism also influences climate change by promoting uplift favorable to prolonged cooling and perhaps glaciation, by opening and closing seaways to ocean circulation, and by influencing atmospheric composition by the generation and consumption of crustal rocks. Though more subtle, climate may in turn affect tectonism by redistributing continental mass through erosion and deposition, thereby generating isostatic adjustments to crustal loading and unloading. Tectonism also influences plant and animal distributions directly, for example by providing linkages or barriers to migration, while climate and biota are intimately linked in the biome concept and the feedback effect of biomes on climatic processes. This chapter examines the interactive roles of tectonism and climate in changing the South American landscape over the 200 million years that have passed since the initial breakup of Pangea. It then discusses the implications of these changes for geomorphology and biogeography, and concludes with a brief evaluation of the pace of landscape change.

This paper describes multidecadal-scale beach changes in the 27-km long Zuma littoral cell, southern California, over 75 years (1928-2002) and suggests explanations based on ocean-climate forcing and other factors. Over this period, beaches within the cell, between Point Mugu and Point Dume, have experienced little human interference compared with other beaches in the region. The methods involve selection of eight target beaches and measurement of changes in beach width from vertical aerial photographs obtained at irregular intervals between 1928 and 2002, supported by archival studies, repeat field surveys and statistical analysis. The photogrammetric data show considerable seasonal and annual changes in width within and between beaches, but also significant trends at longer time-scales. In temporal terms, beach behavior throughout the cell is characterized by short-term episodes of erosion related to seasonal storms and recurrent El Nino events, and longer-term changes that appear to operate in a cyclic manner over decades. The latter we correlate with the Pacific Decadal Oscillation (PDO), as reflected in greater or lesser storminess related to sea surface temperatures across the northeast Pacific Ocean. For most beaches, net erosion coincides in varying degrees with PDO warm phases from 1925 to 1946, and again from 1977 to 2002, whereas net accretion coincides with the PDO cool phase from the 1947 to 1976. The beach-sediment regime is complicated by lag effects, sediment delivered by local streams as storms move onshore, and by reduced seacliff erosion following coastal highway construction. These findings have important implications for coastal management at decadal time-scales.

The opening and closure of the seasonal Malibu river mouth in southern California was investigated over the 1997-98 water year by relating repeat morphological surveys to hydrodynamic variables. The study began with a closed barrier-lagoon system in October 1997, followed by adjustments to artificial breaching and modest floods over the next three months. In February 1998, the barrier was swept away by massive floods and replaced by an open estuary dominated briefly by fully turbulent jets and then by friction-dominant conditions with middle ground bars. Gradual closure from March to July 1998 was effected by (1) onshore migration of offshore bars, eventually forming an emergent barrier, and (2) longshore migration of the narrowing outlet until scaled by bar accretion and littoral drift. Onshore bar migration occurred at initial rates of > 2 m d(-1) that decreased exponentially to < 0.5 m d(-1). Longshore outlet migration increased from similar to 1 m d(-1) to similar to 3 in d(-1). These closure processes reflected the increasing dominance of waves and wave-related currents over diminishing stream discharge and tidal flux. Middle ground bars stranded by winter floods influenced the nature and rate of barrier formation. A new barrier-lagoon system was complete by early August but later breached in response to rising lagoon levels. Seven stages in a spectrum of seasonal river-mouth morphodynamics have broad implications for coastal geomorphology, ecology, and management.