Antony R. Orme

Shifting paradigms in geomorphology: the fate of research ideas in an educational context

The acceptance of new ideas into the mainstream of geomorphological education is illustrated from the development of theories dealing with Earth history, glaciation, uniform flow, mass movement, continental mobility, cyclic erosion, and drainage networks. The lag between the conception of new ideas and their incorporation into mainstream texts has varied from negligible to more than 200 years. On one hand, despite its then untestable assumptions, the Davisian cycle of erosion gained rapid favor as the dominant paradigm of the early 20th century before it was found wanting. In contrast, concepts of uniform flow and slope stability, confirmed in the 18th century, waited almost 200 years for incorporation into geomorphology texts sensu stricto, although they had long been available in books on hydraulics and soil mechanics. Continental mobilism had a wild ride, culminating in the eventual acceptance of the plate-tectonics paradigm in the later 20th century. Explanations for the fate of these and other ideas are varied. New ideas are often opposed by establishment conservatism, language barriers, the perceived surrealism of new concepts, and simple ignorance. In contrast, new ideas may be accepted, sooner or later, by virtue of simplicity, forceful and well-connected leadership, or the death of opponents. Although mitigated by the information revolution of recent decades, these forces still persist and influence the extension of new ideas into a larger arena.

Field Mapping and Computer Simulation of Braided-Stream Networks

Braided stream channels, described and discussed by many writers, still pose problems of origin, geometry, and persistence through time. Recent advances in the classification of deltaic channel networks (of which braids are a subset) and computer simulation of braided networks provide guides to further field and simulation research. We selected small but complete braided units that could be mapped sufficiently quickly to record the minor islands and channels, as well as to measure relative discharge in the channels. Some islands are less than 0.5 m in length, and minor channels may be as narrow as 20 cm, with flowing water less than 1 cm in depth. Topological analysis showed good agreement with expected proportions of the four possible kinds of links generated by combinations of bifurcations (forks) and junctions. A simulation model developed here, based on the number of channels in equally spaced cross sections through the braid, yields output in fair topological agreement with short braided segments of measured real-world input. Enclosure-length distributions in nature and simulation output differ markedly, however, especially in the number of very short enclosures produced by simulation. Our general conclusion is that neither aerial photographs nor published maps are wholly satisfactory for detailed braided stream research. Rapid field mapping is essential for defining the initial stages of braid generation, inasmuch as the smallest components, especially those less than 1 m long, appear to change shortly after new bifurcations occur.

Pleistocene pluvial lakes of the American West: a short history of research

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.

Multidecadal-Scale Beach Changes in the Zuma Littoral Cell, California

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 Niño 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.

Late Quaternary tectonism along the Pacific coast of the Californias: a contrast in style

Abstract Marine terraces and associated features are examined along 1500 km of coast at the seaward margin of that part of the North American plate that has been captured by the Pacific plate. This coast embraces parts of three morphotectonic provinces, each with its own distinctive tectonic style, namely the southern Coast Ranges, western Transverse Ranges, and northern Peninsular Ranges. Based primarily on the 125 ka shoreline, four magnitudes of late Quaternary deformation are recognized: (1) high uplift rates exceeding 1.0 m per 1000 years; (2) moderate uplift rates between 1.0 and 0.1 m per 1000 years; (3) low uplift rates less than 0.1 m per 1000 years; and (4) variable net subsidence. The highest rates of uplift and subsidence are associated with the intense fold-thrust tectonics of the western Transverse Ranges nearest the Big Bend in the San Andreas fault, and diminish in magnitude to east and west. Moderate uplift rates occur in both the southern Coast Ranges and the northern Peninsular Ranges adjacent to the western Transverse Ranges, commonly associated with block uplift and subsidence between high-angle reverse faults within a broader strike-slip scenario. This suggests that compression and transpression are significant features of these areas and that the continued rotation and relative westward motion of the western Transverse Ranges, within the broader context of shear distributed across the San Andreas fault system, continue to have an impact on regions immediately to the north and south. Uplift diminishes with distance from the Transverse Ranges and is low for Baja California south of Punta Banda. The style of late Quaternary deformation is similar to that defined by earlier Quaternary marine limits, but intensity varies, most notably in the western Transverse Ranges.

RELICT BARRIER BEACHES AS PALEOENVIRONMENTAL INDICATORS IN THE CALIFORNIA DESERT

Relict barrier beaches occur around the margins of many former pluvial lakes in the California desert. In common with modern barrier beaches along ocean coasts, these relict barriers possess geomet...

THE UNUSUAL STORMS OF FEBRUARY 1992 IN SOUTHERN CALIFORNIA

During February 1992, a series of relatively warm storms passed eastward across southern California, yielding intense precipitation that triggered widespread mass movement, flooding, property damage, and loss of life. These storms were triggered by an intense low pressure system (976 mb) off northern California which deepened as its eastward progress was initially blocked by a high pressure ridge (1040 mb) across western North America. Between February 10 and 13, large areas of Ventura and Los Angeles counties experienced cumulative precipitation of 200–400 mm with intensities reaching 40–50 mm hr-1. Mass movement, mainly as soil slips that transformed downslope into debris flows, occurred where cumulative precipitation exceeded 300 mm and when sustained intensities exceeded 25 mm hr-1. Stream response was rapid, particularly in urban areas where impermeable surfaces and storm drains fed concrete stream channels. The canalized upper Los Angeles River and Arroyo Simi exceeded all previous discharges for ov...

THE NATURE AND RATE OF ALLUVIAL FAN AGGRADATION IN A HUMID TEMPERATE ENVIRONMENT, NORTHWEST WASHINGTON

Comparatively little is known about net aggradation on alluvial fans, despite fan construction wherever sediment-delivery rates from uplands exceed sediment-removal rates from receiving basins. In January 1983, 20 alluvial fans in the forested Cascade foothills, northwest Washington, experienced net aggradation in response to debris torrents and stream floods triggered by intense warm rains falling on antecedent snow. Five trenches were excavated to 5 m depth on the Mills Creek fan to place the 1983 event in temporal perspective. The deposits reflect normal streamflow, hyperconcentrated streamflow and debris torrent (flow) conditions. One trench revealed residues of 7 events since 1720 BP. Net rates of Holocene aggradation, based on sediments overlying late Pleistocene fluvioglacial deposits, average 0.42 m ka-1. Net rates for later Holocene time range from 2.17 m ka-1 since 1720 BP to 2.36 m ka-1 since 430 BP. These recent rates exceed the local value for the entire Holocene and rates for humid temperate...

Editorial—Physical Geography as an Expression of Change

The practice of physical geography frequently involves studies of change— spatial change as expressed by climate and vegetation patterns, and geomorphic processes and resultant landforms, which vary from one region to another; and temporal change as natural and human processes shape the landscape through time. Apart from the geographer’s traditional interest in spatial patterns and their explanation, the temporal aspects of change have attracted much scientific interest in recent decades, notably in, but not limited to, issues of climate and its many consequences. It could be argued that the many contributions of geographers to the understanding of environmental change and its implications have not been recognized to the extent that they merit, or that such studies are frequently published in journals beyond geography. In this editorial we invite scholars to publish their studies of environmental change in Physical Geography, a journal founded to further the status of the discipline and to ensure that geographers and others have an opportunity to present their research in a geographical outlet and in a timely manner. The journal, now published six times annually, guarantees publication, within two months of final acceptance, of both lengthy research papers and shorter notes and commentaries. Physical geography is many things to many people. A study of Earth’s natural environment: yes! A study of interrelationships between people and environment: certainly! And a study of these relationships through time and space: undoubtedly! But it is more than that: physical geographers seek to understand these and other relationships so as to predict future events, so that in turn we can plan and manage our Earth, its resources and challenges, more effectively for the common good. Physical change occurs in many forms. It may be sudden, vaguely predictable, irreversible and tragic, as witness the Sichuan earthquake in China in 2008. It may be swift but predictable, for example in the impacts of Cyclone Nargis on the Irrawaddy delta in 2008, of Hurricane Katrina along the Gulf coast in 2005, of episodic floods along the Mississippi River, and of recurrent fires in California. The human tragedies associated with these events could have been mitigated by better preparedness, which implies understanding the natural systems involved, planning appropriate land-use scenarios, and managing natural and human resources more effectively. And some changes are much slower, usually predictable, often

Climate Change in Eurasia: Perspectives over Space and Time

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, >105 years), intermediate (Earths orbital relations, 104-105 years), and shorter timeframes (<104 years), emphasizing that climates change more or less continuously in response to many forcing factors (solar output, Earths 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.