Larry Mayer

Distribution of calcium carbonate in desert soils: A model

A model that describes the distribution of calcium carbonate in desert soils as a function of dust flux, time, climate, and other soil-forming factors shows which factors most strongly influence the accumulation of carbonate and can be used to evaluate carbonate-based soil age estimates or paleoclimatic reconstructions. Models for late Holocene soils have produced carbonate distributions that are very similar to those of well-dated soils in New Mexico and southern California. These results suggest that (1) present climate is a fair representation of late Holocene climate, (2) carbonate dust flux can be approximated by its Holocene rate, and (3) changes in climate and/or dust flux at the end of the Pleistocene effected profound and complex changes in soil carbonate distributions. Both higher carbonate dust flux and greater effective precipitation are required during the latest Pleistocene-early Holocene to explain carbonate distributions in latest Pleistocene soils. 21 refs., 4 figs., 1 tab.

Dating Quaternary fault scarps formed in alluvium using morphologic parameters

Abstract Ages of fault scarps, as well as those other types of transport-limited slopes, can be estimated by comparing their morphology with the morphology of scarps of known age. Age estimates are derived by fitting the scarp profiles to synthetic profiles generated using a diffusion equation or, alternatively, by classification using a linear discriminant function. The usefulness of morphology-derived age estimates depends on the relative importance of non-age-related morphologic variation. Data from more than 200 scarp profiles demonstrate that morphologic variation not related to scarp age can introduce significant uncertainties into morphology-derived age estimates.

Subsidence analysis of the Cordilleran miogeocline: Implications for timing of late Proterozoic rifting and amount of extension

Tectonic subsidence of the Cordilleran miogeocline in the western United States during late Proterozoic through early Paleozoic time is best explained by rifting and subsequent thermal contraction of the lithosphere. The tectonic component of subsidence can be calculated by removing the isostatic effects of sediment and water loading. The resultant subsidence curves indicate that rifting began about 600 m.y. ago and that extension of the lithosphere during rifting was in excess of a factor of 1.3.

Active tectonics of the Loreto area, Baja California Sur, Mexico

Abstract Quaternary faulting and coastal uplift characterize the rifted margin of Baja California near Loreto. The process by which strain between the North American and Pacific Plates became partitioned across the Baja Peninsula and the Gulf of California is partially recorded in the tectonics of the Loreto region. The Loreto fault, which consists of a north–south trending northern segment and a northwest–southeast southern segment, records part of this process, as do other faults offshore. During the Pliocene, the southern Loreto fault was actively providing accommodation space for rapid sedimentation in the Loreto basin. Basin subsidence, which abruptly slowed at the end of the Pliocene, was replaced by uplift, which occurred throughout the Quaternary. The Quaternary history of the northern Loreto fault is recorded in fault scarps cutting Quaternary deposits. Fault studies indicate that cumulative normal slip on the northern Loreto fault over the Quaternary was only about 30 m. Latest Pleistocene deposits are offset by about 5 m. Uplifted marine terraces, which may record either isostatic uplift of the coastal region or faulting events offshore, suggest rates of coastal uplift between 0.08 m/ka to 0.16 m/ka for the last 120 ka. These results strongly suggest that since the end of the Pliocene, strain was transferred from the Loreto fault to other faults, probably offshore. Strain between the Pacific and North American plates may, therefore, largely occur in the Gulf of California rather than onshore, in the Loreto region. Despite the low Quaternary strain rates recorded, the offshore faults and the Loreto fault may both represent significant seismic hazards albeit with long recurrence intervals.

Some comments on equilibrium concepts and geomorphic systems

Abstract Equilibrium is commonly used to describe geomorphic systems that can adjust to changes by reaching a steady state. As a conceptual framework, equilibrium emphasizes the relation between present form and process. Systems analysis is a conceptual framework that can be used to quantify and relate material or energy flows that comprise a geomorphic system. Despite the apparent similarity between the language of systems analysis and the descriptive examples of geomorphic equilibrium, these two conceptual frameworks are divergent in many respects. From the vantage point of a systems approach in geomorphology, many types of equilibrium purported to describe geomorphic systems, such as dynamic equilibrium and graded equilibrium, are seen to be very different from one another and in turn very different from the kinds of equilibrium resulting from systems analysis. There are several differences between concepts of equilibrium that serve to illuminate the workings of natural systems in a way that were undefined within each framework. Additionally, several important characteristics of geomorphic systems are analytically invisible using equilibrium concepts, such as spatial self-organization, scale invariance and inherent instability. Time, used quite intuitively in all non-systems definitions of equilibrium, is an important source of insight to the behavior of geomorphic systems. In systems analysis, time is defined by the process under consideration and is not defined a priori as it is with equilibrium concepts. Whereas time consists of a single duration for equilibrium concepts, it must consist of a duration and a smaller interval over which the process is realized for the systems approach. Iterative processes whose affects can be different depending on their sequence, introduce a degree of complexity into the analysis of geomorphic systems that, although long recognized, has been unmanageable because of a predisposition to the use of average rates.

Fractal characteristics of desert storm sequences and implications for geomorphic studies

Abstract Daily precipitation sequences from desert climate stations located in southern California and Nevada exhibit fractal characteristics at time bins less than 100 days and non-fractal characteristics at time bins greater than 100 days. The fractal behavior of these data is described as Cantor dust with fractal dimensions ranging from 0.37 for Bishop, California, down to 0.26 for the Eagle Mountain, California. Due to its nature as a clustered event sequence, computer modelers hoping to simulate geomorphic processes responding to precipitation events such as soil leaching, paleoclimate, lake levels and other processes linked to hydrologic budgets, must use caution in devising time increments for their models. Significant water budget changes are possible without changing long-term precipitation averages, but rather, by changing the precipitation delivery schedule over a period of time. The Cantor dust aptly quantifies these and other aspects of a precipitation sequence and can be used to more precisely characterize a climatic type. Because many geomorphic processes dependent on precipitation are a function of frequency, magnitude and antecedent conditions, the fractal characteristics of the precipitation sequence play an important role in understanding the limits of forward modeling.

Geomorphology–A Systematic Analysis of Late Cenozoic Landforms, 3rd Edition

Geomorphology is the study of how landscapes form. This deceptively simple description encompasses a branch of geoscience that is teeming with fundamental questions of how landscapes develop similar or different morphologies, and whether their developments can be explained historically or modeled theoretically. Geomorphology also involves the surface processes that inexorably convert rock into sediment. Because the study of either landforms or landsculpting is linked to active processes commonly occurring on human timescales, it might be fair to classify geomorphologists as the existentialists of geology.

Time-thickness bar diagrams: Simultaneous display of lithostratigraphic thickness and chronostratigraphic range

Time-thickness bar diagrams present stratigraphic information in a clear and concise manner and are useful for basin analysis. Examples of these diagrams are presented for two basin types—a transtensional basin and a miogeocline.

Effect of storm clustering on water balance estimates and its implications for climate impact assessment

Daily and monthly-based water balance computations are made for areas with climates ranging from humid (Coshocton, Ohio) through Mediterranean (Watsonville, California) and semi-arid (Dodge City, Kansas) to arid conditions (Tucson, Arizona). Monthly procedures lead to an underestimate of observed mean annual runoff by 14% in Coshocton, 59% in Tucson, and an overestimate by 9% in Watsonville. Daily balance calculations increase model accuracy. The improvement in runoff estimates by using the daily method is most significant for arid climates. Daily-monthly departures are greater in the semi-arid and arid areas than in the humid and Mediterranean areas. In terms of mean annual runoff, the difference between monthly estimates and daily estimates is 42.5% in arid Tucson, 58.2% in semi-arid Dodge City, but only 8.9% in humid Coshocton and 5.6% in Mediterranean Watsonville. The daily-monthly departures in soil moisture estimates are generally less than 10% in the humid and Mediterranean climates, but well above 50% in most months in the arid and semi-arid climates. Regression analysis indicates the daily-monthly difference in moisture surplus estimates correlates well with the amount of storm clustering within a month. Monthly computations depart increasingly from daily computations as storm clustering increases. The hydrological impacts of changes in storm clustering are studied by forcing the water balance model with daily precipitation sequences based on hypothetical storm scenarios. Total annual moisture surplus tends to increase with increased storm clustering. In the arid and semi-arid climates, the differences between the most and least clustering scenarios equal 35% up to 60% of surplus water generated by normal storms. They are about 20% in the cases of the humid and Mediterranean climates. These results suggest future potential changes in climatic variability such as storm delivery patterns can have significant impacts on water resource availability.

WBANDZ: a C program to calibrate the hydrologic model and calculate monthly water balance and Palmer's Z -index

Abstract Derived from modified Palmers water-balance model, program WBANDZ simulates continuous monthly time series for major water-budget variables and Palmers Z -index (the monthly moisture anomaly index) based on monthly precipitation and temperature data, and also calibrates the water-balance model by comparing observed and predicted streamflow. The calibration procedure produces optimal estimation of model parameter values which include available water-holding capacities of two soil layers and the coefficient accounting for the lag between moisture surplus and runoff from a watershed. Water-balance calculation results including monthly time series of the Z -index and major state variables in the water-balance model such as streamflow, soil moisture, moisture surplus and deficit, etc. as well as long-term average monthly water budget are output as formatted text files to be used in further analysis. The ability of the program to simulate streamflow is demonstrated by the results on two small watersheds in Ohio and California as the predicted monthly streamflow has a high similarity to the observed data, which is reflected both in the patterns of time-series plots of observed and simulated streamflow and in the correlation coefficients (⩾0.9) and slopes (⩾0.92) of the regression lines derived from the plots of predicted streamflow data versus observed ones.