Landscapes on the Edge New Horizons for Research on Earth's Surface (2010) / Chapter Skim
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2 Grand Challenges in Earth Surface Processes
2 Grand Challenges in Earth Surface Processes
Pages 35-108
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From page 35... ...
Both scientific curiosity and societal demand drive us to read this fragmentary and often puzzling archive in an attempt to understand how the surface environment in which we exist has evolved through time and therefore how it may change As used in this report, the term "Earth surface scientists" refers to scientists from disciplines concerned with the form, 1 composition, properties, function, and evolution of Earth's surface, including biogeochemistry, ecology, environmental science, geochemistry, geography, geology, geomorphology, glaciology, hydrology, oceanography, sedimentology, soil science, and stratigraphy. Increasingly, scientists from disciplines such as atmospheric science, engineering, geophysics, and social science are participating in research on Earth surface processes as well.
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From page 36... ...
in the future. Our growing ability to quantify processes specific to the near-surface environment also lets us reconstruct Earth's past in increasing detail including aspects of its geochemistry, biotic processes, topography, and particle and solute fluxes.
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Landscapes on other worlds also provide a chance to test and expand our understanding of the Earth's surface processes by applying them to materials and basic surface conditions (e.g., gravity, atmospheric pressure) very different from the ones with which we are familiar.
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. These images are used to characterize hydrocarbon reservoirs, but as records of geomorphic evolution, their potential value for understanding surface dynamics is enormous and has hardly been tapped.
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These topographic maps (field of view 8 x 12 kilometers, relief of approximately 600 meters, with 4 times vertical exaggeration) represent a time series of Pliocene (circa 3.5 million years ago)
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From page 40... ...
linking studies of the surface and subsurface. Quantitative Reconstruction Interpretation of landscape records by Earth surface scientists to this point has been mostly qualitative.
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In 2008, NSF supported an international workshop on High-Resolution Topographic Data and Earth Surface Processes to explore how high-resolution topographic data can advance understanding of Earth surface processes (Merritts et al., 2009)
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From page 42... ...
. Physical landscape patterns are often closely associated with biotic ones, ranging from the variation in forest type with upland elevation to riparian ecosystems tied to stream channels to the exquisite control of marsh vegetation by small changes in land elevation and wetting frequency.
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From page 43... ...
Microscopic imaging has also revealed patterns of mineral dissolution at micron scales that are similar to those developed on the scale of landscapes. Measurement of molecular biological signatures has revealed the details of spatial patterns, recognized for decades, in the distribution of biota as a function of depth and position in soils and sediments (see also Section 2.4)
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From page 44... ...
The striping results when biogeochemical processes cause electrons to be transferred to metal oxides containing iron and manganese. The bars represent downward depth in the soil profile.
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Grand Challenges in Earth Surface Processes FIGURE 2.7 The unmistakable human footprint dominates many landscapes. Even someone unfamiliar with central-pivot irrigation systems would have no trouble identifying this pattern as unnatural.
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, the State of Utah Automated Geographic Reference Center (Point of the Mountain, Utah) , and the National Center for Airborne Laser Mapping (remaining three sites, all in California)
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From page 47... ...
to study connectivity, distance-decay functions, shape analysis, edge roughness, and association between patterns show great promise. The need also exists to build stronger linkages between spatial analysis and GIS in the study of Earth surface processes.
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From page 48... ...
Approaches to the origin of landscape patterns span the full range of methods: from classical perturbation and normal-mode analyses to a variety of numerical models including generic evolution equations, coupled systems of partial differential equations, and cellular (for example, coupled map lattice) models.
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How Can We Use Landscape Patterns to Improve Prediction? We are currently faced with the problem of forecasting the response of the Earth surface system to changes that include climate, land use, and sea level.
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. Rates and patterns of deformation in active convergent mountain belts are strongly influenced by the breakdown of rocks and their 0
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This recent insight fosters an entirely new set of research questions that can bring together climate scientists, geophysicists, structural geologists, and Earth surface scientists in an effort to
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Recent findings show that (up to some limit) the faster the physical erosion rates, the faster are the chemical erosion rates.
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and (b) show the results of numerical models aimed at understanding the tectonic response of mountain belts to unidirectional moisture flux.
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Interdisciplinary studies of Earth surface processes provide a geographically and temporally extensive perspective on these problems, which currently are being tackled by local engineering strategies alone. This perspective provides a critical context in which to more fully examine, understand, and address those problems.
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Other linkages between Earth surface processes and global climate that require study involve the sequestration of carbon in the sediments of foreland basins and deltas, the potential for reestablishing carbon storage in soils in the vast cratonic regions that are managed by humans for agriculture and forestry, and the potential for decreases in the carbon reservoir in boreal regions if warming of the soils combined with melt-driven hydrologic and geomorphic disruption causes drainage and oxidation, and methane release. The linkages among surface processes, tectonics, climate, and landscapes operate at geologic time scales (tens of thousands to millions of years)
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From page 56... ...
quantification of the role of climate in surface processes; (2) influence of mountain building and surface processes on climate; (3)
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. Influence of Mountain Building and Surface Processes on Climate Surface processes influence local and global climate in numerous but poorly understood ways through their influence on topography, land cover (ecosystems, albedo)
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Degradation of dryland ecosystems could further reinforce climatic drying and increase dust aerosols globally. Sedimentation and Mountain Building Sedimentation on the flanks of actively deforming mountain ranges significantly influences the rate and pattern of active faulting and erosion rates.
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From page 59... ...
. Three-dimensional imaging of subsurface horizons allows extraction of a time sequence of high-resolution paleo-land surfaces -- a direct record of landscape evolution and a resource that has hardly been tapped to date (see also Section 2.1)
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From page 60... ...
These models can also be used to generate time series of expected patterns of rock uplift and subsidence associated with mantle convection. An exciting frontier of research lies in the coupling of surface process models to mantle convection models to explore potential feedback mechanisms: Can climate, through the agencies of physical and chemical denudation, sediment transport, and deposition influence convection in the mantle?
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From page 61... ...
The breakdown of bedrock -- a major factor in Earth surface processes -- is among the least understood of the important geological processes. The transformation of rock into small and large particles is driven by stresses associated with tectonics, chemical reactions, topography, salt and ice growth, mineral swelling, biotic activity, and thermal fluctuations.
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From page 62... ...
Soil, Earth, and life scientists of all backgrounds are crossing disciplinary boundaries to develop a more integrated picture of Earth's surface down to and including altered bedrock. This new aspect of research on Earth surface processes emphasizes the biogeochemical cycles of all the elements, at all depths, at human-impacted and pristine localities, over all relevant time scales.
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From page 63... ...
The prediction of biogeochemical evolution of water from its arrival as precipitation striking the canopy of vegetation through its reaction with soil and rock to its discharge via rivers to the sea is one of the great challenges in Earth surface processes (see also Chapter 1)
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As part of this latter initiative, data from the CZOs are being compared to data from seed sites within the Critical Zone Exploration Network (CZEN) as well as to the six satellite sites associated with the Pennsylvania CZO to investigate how variations in temperature and precipitation affect regolith formation Aspects of this challenge have been addressed -- though as yet incompletely.
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Network and the emerging National Ecological Observatory Network (NEON) in recognition that questions in Earth science related to the Critical Zone are often best addressed at sites chosen to study specific Earth surface processes.
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The transformation of rock to erodible debris and the shedding of mass through dissolution by subsurface flow influence many processes. Advances in monitoring technologies, geochemical analyses and models, shallow subsurface geophysics, geobiology, nanogeoscience, and rock mechanics will help move the field of Earth surface processes from correlation to explanation and from mapping to prediction.
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. Photographs A through D derive from the Critical Zone Exploration Network site on Guadeloupe.
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A simplified set of mathematical expressions for mass conservation applicable to landscape evolution modeling spotlights the critical need for laws in Earth surface processes. Landscape evolution involves the coupled evolution of two layers (Figure 2.15)
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is derived from airborne laser swath mapping from http://www. opentopography.org, and the Mars image (bottom; NASA/JPL/MSSS)
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From page 70... ...
In the Earth sciences, this research challenge is similar to the need to develop friction laws for faults or temperature- and pressuredependent viscosity models for mantle convection and glacier flow. The large knowledge gap in Earth surface processes is particularly challenging because it requires dealing with complex materials (for example, soil, organic matter, and bedrock)
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Ideally, such parameters would allow us to conduct scaled experiments in the laboratory or to apply transport laws in new settings, such as Mars or Titan. Significant progress has been made recently in developing and applying geomorphic transport laws for soil transport and river incision into bedrock.
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-(J) show spatial variation of hillslope gradient for current and modeled surfaces.
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The founding of the NSF-supported CSDMS (Section 2.3) will encourage the development of sediment transport law theory and its incorporation into landscape evolution models.
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, which are dedicated in part to observing and modeling the evolution of soil and weathered bedrock, will advance significantly our understanding of weathering and landscape evolution. Furthermore, advances in various geophysical tools are enabling us to monitor from space and explore the subsurface in entirely new ways (Box 2.6)
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Geological Survey. qualitatively, even introductory textbooks recognize specific roles that rock properties, climate conditions, and biotic activity play in Earth surface processes and landscape evolution.
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Remote-sensing techniques have proven useful for imaging numerous characteristics relevant to Earth surface processes. Examples include high-resolution imaging of topography, topographic and ice surface change over time, and vegetation; imaging surface velocities of glaciers and mass movements; multispectral imaging of Earth's entire surface and atmosphere every one to two days; and measurement of spatial and temporal variations in rainfall.
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From page 77... ...
documenting fracture density in bedrock, quantifying its influences on hydrology, weathering processes, and denudation; (4) near-real-time monitoring of mass transport across landscapes to improve geomorphic transport laws and geochemical models; (5)
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. Despite our awareness of the role of life in Earth surface processes, we often have only a qualitative appreciation of this connection.
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At present, however, we do not know if microbes affect the shapes of hillslopes or the form of rivers, nor can we quantify how biotic activity influences ecosystem services. We do know that plants and animals such as trees, worms, gophers, and insects strongly influence surface processes and consequently the form and composition of the surface and ecosystem functioning.
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Connections to human activity are also involved. Some have proposed that land use has reduced the crust and vegetation cover of arid lands, leading to more dust erosion, and some of that sediment is deposited in mountain glaciers (as in the Rocky Mountains)
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From page 81... ...
This pattern in turn may direct both chemical and physical erosion rates and, on mountains, affect the spatial pattern of unloading. The pattern of erosional unloading directs the evolution of mountain systems, and by these connections, biota may influence the shape, height, symmetry, and surface chemical composition of mountain ranges.
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From page 82... ...
at SMM. A major new traveling exhibit initiative, HO: Water = Life, developed by SMM and the American Museum of Natural History in New York, along with three STCs, is also helping the public learn about Earth surface processes (http://www.amnh.org/exhibitions/water/)
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From page 83... ...
Although the coupling to Earth surface processes and landscape form, composition, and evolution is not explicitly a goal of NEON, the data gathered will provide a wealth of information for such endeavors. An important opportunity for critical interdisciplinary advances may be missed, however, if biologists focus on NEON sites, Earth scientists focus on CZOs, and hydrologists develop their own observatories.
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From page 84... ...
If riparian and floodplain vegetation is thinned by drought, the floodplain may become erodible by overbank flows, the bank strength may be reduced, and a multithread, less sinuous channel may develop with frequent avulsions, a steeper gradient, higher sediment transport rate, and a higher rate of channel and floodplain change. Such a transition is often labeled "channel instability," but it represents an enduring change in the probability distributions of channel forms and operations, under an altered set of processes, driven ultimately by a change in climate and vegetation in this example.
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. The goals and challenges of research in Earth surface processes include identifying thresholds of change, understanding the environmental processes most
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From page 86... ...
Such correlations have improved in the past 20 years with the availability of digital spatial information for attributes such as topography, geology, vegetation, rainfall, soil depth, and other factors. High-resolution topographic data obtained from airborne laser mapping greatly increase our ability to identify and delineate landslides and to predict their future occurrence.
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Poor knowledge of the spatial pattern of subsurface conditions that control failure also limits our predictive capabilities. Basic research is still needed in this area.
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From page 88... ...
As discussed in Section 2.1, studies of Earth surface response to past changes foreshadow potential future change and clarify the evolutionary trends that produced today's landscapes. Documenting the occurrence and impact of rapid or abrupt climate change events on landscapes is particularly challenging in that it requires high-resolution paleoclimate reconstructions to complement stratigraphic records, as well as documentation of Earth surface response encoded in the physical, chemical, and biotic properties of current landscapes.
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The figure below shows the δ18O ("delta oxygen 18" or the change in 18O concentration) versus depth and age in the Greenland Ice Sheet Project Two (GISP2)
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From page 90... ...
; clarifying past spatial-temporal patterns of mountain glacier fluctuation in relationship to regional climate and ocean-atmospheric circulation; continued development and testing of numerical mountain glacier models and their effects on mountain landscapes over repeated glacial-interglacial cycles; characterizing the role of climate variability on glacier variations; and predicting the distribution, size, and nature of glaciers in the future. Thawing Permafrost At high latitudes and in high-altitude mountainous environments the regolith and underlying bedrock are permanently frozen except for a seasonally thawed "active layer" near the surface.
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From page 91... ...
Coastal areas worldwide are experiencing eustatic sea-level rise that is exacerbated in many areas by subsidence of already low-lying land surfaces. The current situation is alarming because of the number of people living in lowlands within 150 kilometers of the coast; this number has been projected to increase from 3.6 billion in 1995 to 6.4 billion, or 75 percent of the world's population, by 2025.5 Existing estimates of land-sea elevation changes have been made without considering how the effects of subsidence of coastal land areas, altered sediment transport and deposition, or changes in the biosphere may interact with eustatic sea-level rise, which itself varies http://www.aaas.org/international/ehn/fisheries/hinrichs.htm.
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From page 92... ...
A major challenge facing Earth surface process science is to couple biological and ecological processes with physical processes to produce predictive models of coastal landscapes that consider the biological effects on flow and sediment transport and to understand how coastal ecosystems are altered as function of morphology, flow, and sediment transport. Without such coupling it will be impossible to approximate the behavior of these systems.
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Chemicals have entered water and soil through industrial and agricultural practices. Human activity has also been linked to our warming climate over the past several decades, and this warming, in turn, affects Earth's surface processes.
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landscapes that are increasingly altered by humans? This question is among the most pressing challenges of our time, and its scientific component falls squarely within the purview of Earth surface scientists.
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Long-Term Legacy of Human Activity The dominance of humans in shaping some modern Earth surface environments is clear (Figure 1.3)
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. Deciphering what is truly "natural" on an Earth that is not static presents challenging scientific, sociocultural, and policy questions for Earth surface scientists (see also Section 2.9)
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Bottom: The incised meandering streams characteristic of the mid-Atlantic region of the eastern United States were once small anabranching channels that existed within extensive vegetated wetlands; photo shows Western Run at the upstream end of a mill pond. SOURCES: Top and middle used with permission from Anne Chin, University of Oregon.
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From page 98... ...
will improve our ability to address the long-term human impacts on landscapes over the various time scales involved; however, significant challenges remain in data analysis and interpretation. A need exists for increased collaboration between Earth surface scientists and geospatial scientists with expertise in the application of existing and emerging geospatial and remote sensing technologies.
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From page 99... ...
Enormous gaps in knowledge remain, however, especially with respect to understanding the impact-feedback loops within geomorphic systems. Social processes influence both the original human impact and the potential responses and feedbacks within landscape systems -- in other words, human systems influence whether crops are grown on particular soils or how a city is developed, and human systems need to manage and adapt to the
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From page 100... ...
Thus, a primary need in understanding the coupled system is the exchange of analytical perspectives between Earth surface scientists and social scientists, including cognitivebehavioral scientists, economists, political scientists, sociologists, and human geographers. Anthropogenic Earth surface changes also need to be quantified in terms of how they, in turn, affect humans directly or indirectly.
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From page 101... ...
indicate the increased sediment yield caused by deforestation (soil erosion) and other human activity.
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From page 102... ...
Furthermore, the long-term cost of a project will be minimized and the likelihood of its sustainability will be maximized if the original design lies within the stable range of landscape fluctuation and if it respects long-term trends in landscape evolution. To this activity, research in Earth surface processes brings knowledge of how major environmental drivers (such as water regime or sediment supply)
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From page 103... ...
Research in Earth surface processes also focuses on the transport processes that redistribute sediment and chemicals, and interact with biotic processes such as seed dispersal, plant survival, and colonization of aquatic substrates by woody plants, algae, and macrophytes. Attempts to modify the sediment and carbon storage in marshlands and soils require new field studies of the accumulation of organic sediments.
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Many coastal wetlands have very low topographic gradients (see figure below) , so that differences of only several centimeters in salt marsh elevation strongly influence vegetation patterns and ecological and biogeochemical processes.
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, which is about 15 centimeters lower than current sea level. Current tidal ranges are shown at right.
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. Thus, landscape restoration provides an opportunity both for learning and for service by the Earth surface processes research community.
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Grand Challenges in Earth Surface Processes Aging infrastructure, combined with shifting technological practices and environmental values, has con tributed to environmental restoration efforts that include dam removal and stream restoration. Here, the 15-meter-high Marmot Dam on the Sandy River is destroyed in July 2007.
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From page 108... ...
The models may initially be crude and may require sequential elaboration and refinement. Learning how to develop such assessment tools in a politically sensitive, useful way requires that natural scientists studying Earth's surface processes collaborate with social scientists who study all of the other processes that affect the surface, as well as with practitioners in industry, engineers, and planners.
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