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Climatic change and tectonics are two of the most current and intensively studied topics in geomorphology (and paleontology) today. In this volume, the first of a two volume set, the response of landscapes to climatic change is discussed in light of the author's research over the past decade. Professor Bull first presents conceptual models for changing landscapes, then tests and develops concepts in a topical approach, using as his base his extensive experience in the Middle East, western North America, and New Zealand. The basic topics of climate and paleoclimatology, vegetation, soils genesis, and geochronology are discussed in each chapter as essential background and to assess the responses of geomorphic processes to climatic change. Descriptions of present climates are compared with paleoclimatic inferences. Geomorphic thresholds, feedback mechanisms, and response times to perturbations are common themes in the book, which is written primarily for graduate students and researchers.
There is little doubt that climate is an important parameter affecting the shape of the Earth's surface. However absolute observance to the principles of climatic geomorphology leads us away from the study of processes because the analyses passes directly from climate to landscape form. An alternative approach is to examine the effects of climate change on the nature of the processes operating in the near surface environment. Utilizing this methodology, the climate-process relations take on greater significance, and lead to an understanding of the response(s) of geomorphic systems to shifts in climatic regime. Given that geomorphic systems respond to changes in climate regime, it should also be true that delineation of the changes in the types, rates, and magnitudes of geomorphic processes will provide insights into the timing and nature of past shifts in climate, particularly effective moisture. It is this approach that has been utilized herein. Specifically, geomorphic responses in eolian, lacustrine, and fluvial systems that have resulted in erosional and depositional events have been documented for several sites in Nevada (Figure 1), and used to infer the timing and character of climatic change in the Basin and Range Physiographic Province. The results and conclusions of the specific studies are provided.
Geomorphic change along the lower Clackamas River is occurring at a millennial scale due to climate change; a decadal scale as a result River Mill Dam operation; and at an annual scale since 1996 due to a meander cutoff. Channel response to these three mechanisms is incision. Holocene strath terraces, inset into Pleistocene terraces, are broadly synchronous with other terraces in the Pacific Northwest, suggesting a regional aggradational event at the Pleistocene/Holocene boundary. A maximum incision rate of 4.3 mm/year occurs where the river emerges from the Western Cascade Mountains and decreases to 1.4 mm/year near the river mouth. Tectonic uplift, bedrock erodibility, rapid base-level change downstream, or a systematic decrease in Holocene sediment flux may be contributing to the extremely rapid incision rates observed. The River Island mining site experienced a meander cutoff during flooding in 1996, resulting in channel length reduction of 1,100 meters as the river began flowing through a series of gravel pits. Within two days of the peak flow, 3.5 hectares of land and 105,500 m3 of gravel were eroded from the river bank just above the cutoff location. Reach slope increased from 0.0022 to approximately 0.0035 in the cutoff reach. The knick point from the meander cutoff migrated 2,290 meters upstream between 1996 and 2003, resulting in increased bed load transport, incision of 1 to 2 meters, and rapid water table lowering. Ninety-six percent of the total migration distance occurred during the first winter following meander cutoff. Hydrologic changes below River Mill Dam, completed in 1911, are minimal but a set of dam-induced geomorphic changes, resulting from sediment trapping behind the dam, have occurred. Degradation for 3 km below the dam is reflected by regularly spaced bedrock pools with an average spacing of 250 m, or approximately 3.6 channel widths. Measurable downstream effects include: 1) surface grain-size increase; 2) side channel area reduction; 3) gravel bar erosion and bedrock exposure; 4) lowering of water surface elevations; and 5) channel narrowing. Between 1908 and 2000, water surface elevation dropped an average of 0.8 m for 17 km below the dam, presumably due to bed degradation.
This book, first published in 1982, is a collection of articles aimed at advancing the field of geomorphology. It starts from the position that a meaningful grasp of landscape evolution would depend upon an understanding of the present spatial distribution of processes and process rates; comparison of spatial versus temporal change; and careful appraisal of the character and composition of the stratigraphic record. Each article uses a data set to address between threshold variability in either a spatial or temporal context, and often both.
The tropics provide the key to understanding much biological and Earth science. This is particularly true for the study of landforms, which in higher latitudes suffer great seasonal contrasts in process intensity and type, and which often in the past underwent the dramatic changes of glaciation and periglaciation. Yet studies in the tropics have shown that the legacy of past climate changes is much more dramatic than was formerly believed. This book, first published in 1985, brings together the variety of evidence about such environmental changes, over a variety of timescales, and sets it against the current knowledge of the nature of geomorphic processes in the tropics.
This book presents chapters, written by leading coastal scientists, which collectively depict the current understanding of the processes that shape barrier islands and barrier spits, with an emphasis on the response of these landforms to changing conditions. A majority of the world’s population lives along the coast at the dynamic intersection between terrestrial and marine ecosystems and landscapes. As narrow, low-lying landforms, barriers are especially vulnerable to changes in sea level, storminess, the geographic distribution of grass species, and the rate of sand supply—some barriers will undergo rapid changes in state (e.g., from landward migrating to disintegrating), on human time scales. Attempts by humans to prevent change can hasten the loss of these landforms, threatening their continued existence as well as the recreational, financial and ecosystem service benefits they provide. Understanding the processes and interactions that drive landscape response to climate change and human actions is essential to adaptation. As managers and governments struggle to plan for the future along low-lying coasts worldwide, and scientists conduct research that provides useful guidance, this volume offers a much-needed compilation for these groups, as well as a window into the science of barrier dynamics for anyone who is generally interested in the impacts of a changing world on coastal environments.
A statement from the world's leading geomorphologists on the state of, and potential changes to, the environment.
Climate Forcing of Geological Hazards provides a valuable new insight into how climate change is able to influence, modulate and trigger geological and geomorphological phenomena, such as earthquakes, tsunamis, volcanic eruptions and landslides; ultimately increasing the risk of natural hazards in a warmer world. Taken together, the chapters build a panorama of a field of research that is only now becoming recognized as important in the context of the likely impacts and implications of anthropogenic climate change. The observations, analyses and interpretations presented in the volume reinforce the idea that a changing climate does not simply involve the atmosphere and hydrosphere, but also elicits potentially hazardous responses from the solid Earth, or geosphere. Climate Forcing of Geological Hazards is targeted particularly at academics, graduate students and professionals with an interest in environmental change and natural hazards. As such, we are hopeful that it will encourage further investigation of those mechanisms by which contemporary climate change may drive potentially hazardous geological and geomorphological activity, and of the future ramifications for society and economy.
Our views and understanding of variations in climate, geomorphological processes and the interrelationships that exist between climatic changes and land surface changes, both now and in the past, have developed greatly over the last decade. This book aims to encapsulate some of these recent advances and focuses on the integration of research that has been conducted by geomorphologists and climatologists on linking climate and land surface changes. This book is divided into two main parts: Section A incorporates research that has concentrated on short-term variations in climate, whilst Section B looks at some of the work on long-term climate variability. The volume concludes with a summary chapter that brings together the various ideas that have been presented in this work and other recent research in this general field. This text will be of interest to upper level students of geomorphology, Quaternary studies, climatology, earth sciences, and environmental studies. It will also be of use to researchers in these fields.