A Workshop on Desert Processes, September 24-28, 1984; report on the conference

U.S. GEOLOGICAL SURVEY CIRCULAR 989

Department of the Interior

Introduction •..•....•.....•...•.................•......................... 1 Outline of the workshop ......•...............•......•.................. 1 Acknowledgments ........•.••.....•...........•.......•.....•......... 2 Objectives and recommendations of the Desert Workshop .....•.•.•...••.......• 2 Part 1: Summary of discussions ....•.............•..............•....... 2 Part II: Recommendations for collaborative research ...••.................. 5 Contributions from workshop participants Part 1: Monitoring of Processes in Arid Environments ..•.•......•••......... 6

Part II: Relevance to Paleoclimatic Studies ..•....••••...••••.•..••...... 15

References cited ........••••••.••..••••••••••.••••.•••..••••••.••.•.••.. 19 Participants in Desert Processes Workshop ••••••.••..••...•••••....••..•.••.. 20

Figure 1.

General statement, by Juergen Reinhardt. .•..•.••...•••.•••••.•••.••.. 15 Magnitude of changes in past climates, by G.I. Smith •••........•...•...• 16 Investigating climate change, by Stephen G. Wells ....•......•.......... 16 Remarks on desert research and data sources, by Theodore Oberlander •.•..••..•••••••.•..........•.••..••..•... 17 General comments, by Erhard Schulz •............•....•.....•......•.. 18 Interpretation of arid landscapes: Some general ideas for future research, by John C. Dohrenwend ••••...............•......•. 18 Human factors in arid lands, by Howard Wilshire •....•.••....••...•..•.. 19

Map of western North America showing regional context

Mosaic of Landsat images showing features of Great Basin

Oblique high-altitude aerial view of parts of desert

Photographs showing two key localities that illustrate

Location map of USGS Geomet station sites in

Photographs showing instrumentation at Gold Spring

Techniques and standards for measurements at Geomet Page

of Arizona deserts •.••.••••.•••••••.•••••••••..•..••••...•••. 2

Desert in northeastern Arizona •.••.•....•....••••••••••.•••••. 3

covered by field trip •.•.•••...•••••••••.•••••••••••••••••.•.• 4

topics discussed in workshop •••.••.•...•...•..•...•••...•••••• 5

Arizona deserts ••••••..•.•.••.••..••....•••••••.•••••.•••..• 7

Geomet station .•••••.•••..•.......•...•.••••...•••.••••••.• 8

III During the last decade, desert research has seen renewed emphasis as a result of satellite data. improved physical access, military considerations, and economic desertification and resources. Geologists within the U.S. Geological Survey (USGS) have long been involved in desert geology of the Earth (and of Mars since before the first Mars Orbiter Mission, Mariner 9, in 1971). USGS investigators pioneered the use of Landsat remotely sensed data distribution and morphology of large-scale sand dunes in desert regions (Breed and others, 1979; Breed and Grow, 1979) and have recently been using Space Shuttle Imaging Radar (SIR) to de fine newly discovered paleodrainages in the Eastern Sahara of northern Africa (McCauley and others, 1982, 1986). present. At geometeorological conditions in different types of deserts in Arizona, using data relayed by satellite from solar-powered "Geomet" stations (McCauley and others, 1984). automated data-collection platforms coupled with an array of sensors that measure boundary-layer atmospheric and geologic conditions at frequent intervals, around the clock. Such data are essential to studies of surface geologic processes in deserts, particularly wind erosion, and of the land forms that develop in response to these processes.

The Geomet data are also of interest to the U.S. Army, which must operate in various types of deserts and therefore needs information related to natural hindrances to cross-country movement, selection of aircraft landing sites, cover and concealment, camouflage, dust generation, and location of usable water. The U.S. Army Engineer Topographic Laboratories, Center for Remote Sensing (ETL-CRS), has evaluated a variety of remote sensors and image-analysis techniques in subhumid regions, and a part of its research program is directed toward applying these

u.s. Army Engineer Topographic Laboratories,

Fort Belvoir, Virginia 22060. concerns overuse of ground-water

to study the regional

These stations consist of

By John F. McCauley and Jack N. Rinker

is monitoring techniques to the Army's need for information on desert terrain. The complementary research needs of the USGS and ETL-CRS resulted in a workshop held in Flagstaff, Ariz., on September 24-28, 1984, to bring together some of the leading workers in desert processes to exchange information on current programs, to establish general limits of knowledge, to identify areas of research and their priorities, and to discuss the application of results to civil and military problems.

Outline of the Workshop

The plan was to convene a small but focused workshop that would include participants with a broad range of field experience in deserts, to review the overall state of knowledge of desert regions (primarily in the United States) and to attempt to define research directions, tools, and strategies that might be employed in future work. Some of the participants were concerned with experimental methods to determine the physical and chemical bases of present-day surface processes; others used the results of these processes-various types of landforms, sedimentary deposits, and surface coatings-as evidence for interpreting past environments and predicting future conditions. The purpose of the workshop was not to provide an outlet for presentation and publication of formal papers, but rather to provide a forum for lively The individual discussion about selected topics. presentations were informal briefings designed to bring others up to date on current work and opinions.

The workshop was divided into three parts: (1) informal presentations of the highlights of past and current research by the participants as a basis for discussion, (2) aerial and ground field trips to key localities in the Great Basin Desert northeast of Flagstaff (fig. 1) to illustrate the general character and state of knowledge of surface processes and resulting landforms in these arid parts of the southwestern United States, and (3) reassembly of the participants in Flagstaff for two days to discuss processes in the American arid lands in the light of each person's experience.

During the opening sessions, participants presented their thoughts as a means of self-FIGURE 2.--Mosaic of Landsat images showing features of Great Basin Desert in northeastern Arizona.

particle counter that records numbers of suspended dust particles larger than 5.0 1-lffi in diameter; the sand trap includes a tipping-bucket mechanism that measures amounts of windblown sand collected per unit of time. measure the dust and sand flux passing the station and to transmit this information simultaneously with the recorded wind speed and direction. The actual sediment flux that occurs under monitored meteorological conditions can then be compared to the potential sediment-moving capacity of wind predicted by theory. theoretical and actual capacity of the measured winds at each site may then be attributed to variables such as the characteristics of the surface materials, topography, rainfall patterns, and type of vegetation cover.

After field testing of the prototype flux sensors, the other stations will be similarly equipped. instruments directly measure some elements of sediment transport during the real-time wind erosion process. workshop for additional field measurements and for improvements in the Geomet instrument array. The current approach is to obtain detailed data for use in theoretical transport equations, and to develop such equations to calculate the potential for wind erosion of various natural desert surfaces. Beyond this effort, however, research in eolian processes requires a capability to observe and measure the actual removal and redistribution of sediment by wind. Two problems are apparent in pursuing this capability, as pointed out by D. MacKinnon. First, measurement of sediment particles as passive elements in a dynamic process is extremely difficult, especially in an uncontrolled, abrasive field environment. Second, only short-term funding has been available for new instruments that will require long-term development. presently limited to mostly indirect measurements and to theoretical models as representations of the actual process. We should keep in mind that future advances in geophysical studies of wind erosion will require direct measurements of the actual process, and we should pursue the means to accomplish them.

Key Factors in Arid-Land Monitoring Efforts

U.S. Dept. of Agriculture Wind Erosion Lab ora tory

It has been said that our knowledge of something is limited by the extent to which we can measure it and its properties and (or) its influence on something else. requires constant vigilance to ensure that the numbers being stored represent the truth. Ideally, measurements at the USGS Geomet sites should be These sensors are automated to

Suggestions were made in the

Manhattan, Kans.

Any measurement system sufficient to allow calculation of energy, water, and momentum balances.

received at the Earth's surface is distributed according to the function

where R.n is net radiation, L is latent heat of evaporation, Et is evapotranspiration (the amount of water evaporated from soil and transpired by· plants), S is energy utilized in heating soil, A is heat utilized in heating the air, and M is energy stored by plants through photosynthesis. (This last value is comparatively small and commonly neglected.)

2. Water balance.--Water balance is determined

by partitioning precipitation P as follows:

where Et is evapotranspiration, R is surface runoff, D is water entering the ground water through deep percolation, and 6.S is change in water storage in the profile.

3. horizontal momentum to the surface can be estimated from measurements of friction velocities:

where -r is surface shear stress, p is air density, and u* is friction velocity. The friction velocity can be determined from measurements of wind speed in the boundary layer and use of the log-profile law:

z where U is mean wind speed at height z, k is the von Ka1man constant (0.4), d is wind speed displacement height, and z9 is the roughness parameter. The terms z0 and d are characterized by the surface configuration and can be determined from wind-speed-profile measurements. The term 4l is a correction for adiabatic influence and is a function of the Richardson number, R·. The term 4l in equation 4 is usually negligible w~en the wind speed is high enough to cause wind erosion and is commonly neglected. The Richardson number, an indicator of thermal stability, can be expressed by:

where g is acceleration temperature, and

temperature and wind-speed gradients, respectively. Energy balance.--The net solar energy

Momentum balance.--Vertical transfer of

u*

ez - el

zz - zl

of gravity, e is potential

u*

w

(actual soil moisture) 0.5 w (potential moisture at 15 b pressure)

and is measured in newtons/m2.

6. Vegetative cover. Equivalent to R of WEL, part of Lc of Gillette.
7. Sediment transport.
8. Ridge roughness (K). Can be ignored, as it is an insignificant influence on erosion of desert surfaces. B.

monitoring? record is 5 years, which is only a snapshot. For comparison, the longest period of record for geophysical monitoring in the United States is that for co at Mauna Loa, Hawaii, a period of about 30 years. A reasonable minimum would be 10 years, but the lifetime of project funding is usually much less, and a problem of data storage usually develops.

G.I. Smith, U.S. Geological Survey,

Several geologic processes depend on the chemical activity of water in soils. This factor differs from moisture content because even after all liquid water has been lost, water in vapor form continues to react with minerals, although in some instances at lower effective concentrations. The effective concentration of water (a~o) is defined as the ratio of the activity in a particular solution to the activity of pure water, under the same conditions of temperature and pressure. chemical activity of any water in vapor form is the ratio of the partial pressure of the water vapor in question (pH that is in equilibrium with pure water, under the same conditions of temperature and pressure (p* ~0) These ratios are numerically related, by definition, humidity" (RH):

Therefore, when both liquid water coexist in a soil, if at equilibrium,

and if the water is pure,

and RH = 100 percent.

A device to measure the activity of water in soil gases in the field has been devised by Fred Trembour (USGS, Denver). It is most useful for long-term (about 1-year) measurement of (1) relative humidity, or aH a succession of horizons in a soil or rock. The values measured are the integrated effective chemical activity and temperature, as they pertain What time scale is optimum for The minimum acceptable period of

PH 0 --::-*--- X 1 00 PH 0

PH 0 Menlo Park, Calif.

, and (2) temperature at to an ongoing chemical reaction, for the period of measurement. these variables, and gaining a knowledge of them by other means is difficult or expensive or both. The sensors are two plastic vials, calibrated in the laboratory for rate of water loss as a function of temperature. The vials are partly filled with water and buried at the same horizon in the soil. One is exposed to the soil atmosphere, and the other is encased in a desiccant. The "exposed" vial loses water in proportion to the combined effects of temperature and the relative humidity of the soil gases; the other vial, in a relative humidity of 0 percent, loses water solely as a function of temperature. weighed each year.

The author and I. Friedman have been testing these devices in the southeastern California desert. We have data for 1 year (4/83 to 4/84), and the method appears to be producing reasonable results. However, more testing and better methods of annually placing and removing the sensors are needed.

U.S. Army Engineer Topographic Laboratories, Center for Remote Sensing,

Research of the Center for Remote Sensing (CRS) is directed toward the development and evaluation of remote-sensing techniques for obtaining general terrain information and for detecting specific items, materials, or conditions. Information is needed in subhumid regions for such factors as probable locations of usable water, surficial characteristics affecting cross-country movement and aircraft landing sites, potential for dust generation, and soil-mantle depth and characteristics. Involved in these research efforts are analyses of image-pattern elements and the correlation measurements. relations have been established among landforms, soil texture, and vegetation, between landforms and types of materials, and between vegetation and depth of soil mantle, but many more relations remain to be evaluated for their practicality and universality.

We recognize a critical need for fieldwork on eolian processes in desert regions. Such work should include long-range measurements of wind-velocity profiles, of surface characteristics (including vegetation), of soil-mantle characteristics, and of characteristics of the airborne sediment load. The USGS Geomet sites are a first step in this direction, and more sites should be set up. Instrumentation at each site should be expanded both laterally and vertically. Because this undertaking will be large, All chemical weathering involves

The vials must be removed and

Fort Belvoir, Va.

of spectral and radiometric Over the years, many useful and because the information is needed by several agencies, it should be a joint effort as far as possible m terms of money, equipment, and personnel. Although the USGS Geomet stations and the ETL-CRS instrumented test sites were established for different purposes and are in different climatic zones, they collect similar types of information. toward the radiation environment and an evaluation of the factors that influence it. Consequently, our site at Fort Belvoir is instrumented so that we can measure different backgrounds and targets for soil moisture and temperature profiles, wind speed and direction, dew point, soil heat flux, incoming and outgoing radiation, 14~m wavelength band). used at the CRS site is appended.) measurements are the minimum that we need to understand characteristics of surfaces and their corresponding radiation variations. Note that these same factors- -soil moisture, thermal conductivity (heat flux), and temperature--also establish the susceptibility of a given soil to wind movement. Because the USGS is interested characteristics of the airborne sediment load in relation to measurements and instrumentation needs overlap those of ETL-CRS. measurement measurement of soil moisture, heat flux, radiation exchange, and the infrared radiation brightness of surfaces. The predictive models that we are developing are limited to moist temperate regions. We need to extend such models into arid regions, and the Geomet sites can provide the needed measurements. With more instruments, they can enlarge their data base to support other modeling efforts (NASA/Goddard, Optimetrics/ Air Force, and the U.S. Army Engineer Waterway Experiment Station or USAWES).

To better depositional processes in unconsolidated materials and to develop realistic models, measurement of the texture of the airborne sediment load in relation to wind velocity and soil-mantle characteristics is critical, and this effort must be increased. As no suitable device for measuring characteristics of the airborne sediment load over long periods of time is yet developed, this phase will in itself be experimental. Because vegetation acts as a barrier or filter to the wind stream at the surface and thus greatly alters air-flow characteristics, it should be examined in greater detail with reference to spacing, species, envelope shape, internal structure, and porosity.

Of necessity, the Gold Spring Geomet site had to be fenced to protect it from grazing cattle. This fencing has noticeably changed the vegetation, at least its density: the enclosed area now supports more vegetation than does the area outside, and is and

of Our CRS research is directed

The exceptions are their sediment

understand (A list of the instruments

and probably no conditions. The Gold Spring station has, in itself, induced arrangement. We should be able to find a better type of tower that we all could use, one that is stable, portable, easily erected and taken down and one that offers a minimum of wind resistance. Those measurements, and modeling should, as a group, visit each agency's instrumented sites and the proposed Jornada site and prepare a joint recommendation for an increase in instrumentation.

Instrumentation at the ETL-CRS Test Site,

(distances are above, below, or at ground surface, as appropriate)

Air temperature, Tower 1: 10, 50, 120 em, 2, 3 m Air temperature, Tower 2: 10, 50, 120 em, 2, 3, 4, 6, 8, 10, 12 m Soil temperature, Plots 1-4: 1, 4, 10, 20, 40, 80, 160 em Soil heat flux, Plots 1, 2: 4, 12 em Soil moisture, Plots 1-4: 4, 12 em Precipitation, tipping bucket method Dew point temperature Wind speed, Towers 1, 3: 120 em Wind speed, Tower 2: 15 m Wind direction, Tower 2: 15 m Incoming short-wave radiation (Swi): 0.28-2.8llm Incoming long-wave radiation (Lwi): 3-50llm Net short-wave radiation, Plots 1-3: 0.28-2.8llm Brightness or apparent blackbody temperature Surface features: Plots 1,4, cut grass, Plot 3, uncut grass, Plot 2, bare soil, Plot 5, gravel M114 armored reconnaissance vehicle

Characterization of Vegetation and other

U.S. Army Engineer Topographic Laboratories Center for Remote Sensing, Fort Belvoir, Va.

Vegetation stabilizes the soil surface and, by altering the flow of air and water, affects deposition and erosion of surface particles. At all sites of sensor systems or monitoring nets, two types of maps should be prepared, one showing distribution of plant communities and geomorphic features, and the other showing distribution (in percent) of bare, inorganic surface and of each of the three vegetation types listed below.

The total vegetative cover is divided into its physiognomic (life-form) parts, for each of which the cover, height, and seasonality should be described. simplistically as:

longer representative of local

The vegetation can be described and needs a "cleaner"

Fort Belvoir, Va. have been merely modified and enlarged by wind erosion. Chemical weathering is active even in an arid environment, particularly in porous, fractured rocks. Although desert varnish and other coatings and crusts may effectively seal the rock surfaces, fractures allow moisture to enter the rocks. Formation of salt crystals, and the freeze-thaw mechanisms that accompany great variations in diurnal temperatures, may strongly affect landform development in arid lands. Subsurface weathering above the water table has been suggested as the primary cause of many landforms in fractured sandstone and granitic rocks in presently arid or semiarid regions; such fractures not only may have controlled the development of these landforms in past, more humid, temperate environments, but they may also control development in today's arid environments. In porous, highly fractured rocks, the variations in fracture spacing, fracture type, and grain size may control the shapes of resultant landforms, whereas the amount of moisture available may merely affect the rate of their development.

Laboratory of Climatology/Department of Geography, Arizona State University,

The establishment of the USGS Geomet network is an important beginning in understanding desert processes interface. Climatic investigations in three areas can enhance the current effort: (1) increased measurement affecting air movement near the surface and transport of particles; (2) development of full heat-balance relations, including all aspects of the radiation balance; and (3) relation of the Geomet station observations to the regional climatic net work and synoptic climatology.

The first issue has been addressed by J.F. McCauley E.L. Skidmore in this report. The second question is considered by Skidmore and J.N. Rinker, but I would like to elaborate upon it. The chain of events that produces desert landscapes relies on important links to the atmosphere, especially heat balance and water balance. These factors, in turn, significantly affect weathering processes, rates and timing of eolian erosion and transport, and the nature of the vegetation cover (expressed in surface roughness).

The full set of heat-balance components should be known in order to allocate meteorological cause and effect. long-wave depending on such factors as surface material, soil moisture, and snow cover. These differences feed back through the weathering system and the and

Tempe, Ariz.

For example, short-wave and the

D.A.

fluxes react differently earth-atmosphere

Gillette, and production of movable sediment grains. We need not, however, monitor all heat-balance components (or the elements from which they are determined) on a continual basis. The time and cost prohibitions are serious. In any event, sampling by season and weather type can provide a satisfactory link to process. Such sampling can be accomplished with 48-hour runs of a portable instrument array that can be brought to each Geomet site as appropriate. These measurements are an example of how cooperative efforts with other organizations (such as universities and the Office of the State Climatologist) could expand the instrument and personnel base.

Heat-balance discriminate transfers by sensible heat, latent moisture flux, conduction toward or away from the surface, and radiation. A basic measurement array should include two levels of temperature, vapor, and wind speed; incoming and outgoing short-wave radiation; incoming all-wave radiation; net all-wave radiation; two levels of ground temperature; temperature of precipitation under snow-cover conditions; and soil moisture. If possible, infrared thermometers should also be available to measure ground, cloud, and sky temperatures. Important goals of this effort should be to obtain meaningful comparative data and to explain the interplay of land-surface properties with physical climatology in the several desert types under study.

One of the major gaps in climatological research is the determination of scale linkages between micro-, meso-, and macro-climatic events and phenomena. provide an excellent opportunity to attempt to relate sets of highly localized data to ongoing longer term, synoptic weather patterns. relations require analysis not only of daily Geomet station weather but of surface and 500-mb weather charts and of satellite weather imagery.

We are just beginning to realize many of the potentials for remote sensing as finer resolution imagery is being developed. We still need to make meaningful ground-truth imagery. Both the interface physical climatology and synoptic assessments discussed above provide excellent means to this end.

U.S. Geological Survey, Reston, Va.

Recognizing that local climate is a complex interplay of many factors both physical and biological, we must increase our efforts to understand local climates and their perturbations. Integration of data from Geomet stations over various time periods should enable us to understand investigations

The Geomet desert stations

of the better the differences in scales of change-- oscillations, fluctuations, or discontinuities--that may be recorded in the sedimentary record of desert environments. The uniqueness of every desert and of virtually every spot in the desert requires that our data sets be horizontally integrated, but without degrading their quality. Data have been collected in an integrated manner in a variety of other sedimentary environments. For example, along shorelines, long-term tidal gauge records indicate that the eustatic sea level is rising, yet local marine regression is being produced (at least in the short term) by deltas and barrier islands that are prograding due to a local surplus of sediment. Similarly, local perturbations in surface or groundwater flow or changes in wind pattern can produce local changes in aridity that are out of phase with worldwide or even regional trends.

Magnitude of Changes in Past Climates

G.I. Smith U.S. Geological Survey, Menlo Park, Calif.

Abundant evidence exists for major changes in past climates in all parts of the world. In arid regions, now identified by their low precipitation relative to evaporation and evapotranspiration, evidence of less aridity in the past is abundant, but evidence of greater aridity appears to be less commonly recorded.

Studies of the magnitude of past climate change in now-arid regions must first identify the elements of climate (such as precipitation, temperature, wind, humidity, storm tracks, and seasonality) that are of most interest. Most paleoclimate indica tors ("proxy data") are indirect of several elements of climate. indicators Interpretive difficulties arise from this ambiguity when reconstructing past climates themselves. However, many measurements of the proxy data--of stream-flow increases, erosion intervals, lake expansion or shrinkage, periods of aridity and eolian activity--are records of geologic processes, and for purposes of reconstructing variations in nearsurface geologic processes caused by climate changes, they are direct measurements.

Both the intensity and magnitude of past climatic cycles also set the stage for the character of the landscape that preceded the present. Knowledge of this starting point is necessary to reconstruct correctly the processes that led to the present landscape, as some of its characteristics may have been inherited from the earlier forms.

My own interests lie in the fundamental causes of major climatic change. Much evidence indicates that high-latitude, glacial-interglacial cycles are forced, in part, by the global orbital perturbations that become most additive on cycle lengths of about 20,000, 40,000, and 100,000 years. Some evidence exists, however, that although these cycles are represented by variations in the lowlatitude sea-surface temperatures and Caco content, and by mid-latitude continental pluvial changes, the pluvial cycles of largest magnitude found in the record are forced by a 400,000-year orbital eccentricity. Much more work needs to be done to test the latter hypothesis.

University of New Mexico, Albuquerque, New Mex.

Climatic changes involve changes in the solarenergy regime of a given region that affect (1) water hydrology, (2) air movement, and (3) heat energy (temperature). The adjustments of these variables to climatic change are recorded in the geology of the earth's surface. A problem facing those who attempt to interpret climatic changes from the geologic record is to determine the sensitivity of a particular geomorphic system to climatic change, and therefore how well it records climatic change. As indicated in this workshop, our present understanding of how the atmosphere and the earth's surface interact in modern times is poor; therefore, attempts to reconstruct past interactions are at least as poor.

Because the earth's surface is the boundary where the biosphere, atmosphere, and hydrosphere interact with geologic processes, the surface geologic record reflects many factors in addition to climate. accurately, these other variables must be studied, too. As pointed out by Schumm and Lichty (1965), the variables can be classified as independent and dependent:

Time (geochronology)

Geology (lithology, structure) Climate Tectonic relief

Evaluations of interactions (past and present) between climate and the earth's surface require that processes be analyzed over time scales that are appropriate to the methodology and degree of accuracy available. climatic change on geologic processes could be evaluated for the following time periods, using the following methods:

1. Historic (less than 200 years ago): by long-term monitoring using Geomet stations, photoarchive analysis, and satellite imaging.

In order to evaluate climatic effects

For example, the impact of Dependent

Vegetation Total sediment yield Total discharge Morphology and other landform characteristics

2. Holocene (200 to 10,000 years ago): by carbon-14 and cultural-artifact dating to develop a time framework and identify moderate climatic fluctuations.
3. Pleistocene (more than 10,000 years ago): by K-Ar, desert varnish, and other absolute dating methods to develop a time framework and identify large-scale fluctuations in climate.

The problem then is, how comparable are the time scales for analog models? historic and Holocene periods may have more validity than comparing data for historic and Pleistocene periods. The use of modern geologicclimatic relations as analogs for past or future conditions must involve a clear understanding that what we see in the present landscape also reflects past processes and events. Attempts to compare one geographic area with another by relying entirely upon remote-sensing methods are difficult and often unsatisfactory, in that the history of one area may differ significantly from another. An area's history cannot be filtered from any analog model.

The study of climatic change for a given time scale and region should involve the following aspects: timing of climatic change; (2) the sensitivity of earth's surface systems to climatic change; (3) the sequence of responses by earth's surface processes; and atmospheric, biologic, and hydrologic processes during Geomorphologists understand and quantify the interdependence of modern systems, but these studies have not been truly interdisciplinary. workshop, future studies should be interdisciplinary.

Remarks on Desert Research and Data Sources

University of California, Berkeley, Calif.

Research on desert processes could have two alternative goals: (1) to characterize and quantify the environments, as at the USGS Geomet stations, or (2) to explain the visible · details of desert landscapes, which record past as well as present influences, and which may, in fact, be the result of oscillations between processes of different types or intensities. The necessity for the first type of study is too obvious to require further emphasis. Obvious examples of the second type are exposed granitic pediments that formed by slope retreat under semiarid conditions, followed by regolith stripping triggered by loss of vegetative protection due to increased aridity. Much more compressed in time is the phenomenon of cyclic arroyo cutting and filling, which may be either regional or local in scale, depending upon the nature of the triggering mechanism. The point is that process measurement (1) the causes, types, magnitude, and

currently Comparing data for

As indica ted in this

change.

desert at a specific time (the first goal) may or may not explain all the visible features of desert landscapes, which is a separate problem.

Of course, we can learn the specifics of processes operating in the desert environment by collecting data on what is happening today. But not necessarily only in deserts! effect of process oscillations we also need data from areas both more arid and less arid, to provide the full range of climatic possibilities that may have been relevant to desert landscapes throughout the period of their development. studies in progress now or in the future in nondesert settings may be pertinent to desert landscapes. Many studies have been made of pediments in the southwestern United States, where they are one of the most conspicuous of all desert landforms, but the studies are inconclusive. The problem is that nearly all of them are studies of moribund pediments, some stagnant for millions of years. The "live" ones, still expanding by vigorous slope retreat, and still unstudied, as far as I am aware, are not to be found under desert shrubs, but in wellvegetated locations such as the Sierra Prieta, west of Prescott, Ariz. (Willhoit-Skull Valley area), under chaparral scrub and grass. To understand pediment formation we need information on processes affecting such places.

Perhaps some sort of data bank or clearing house should be set up for measurements of environmental processes, with attention to the exact characterization of both the climatic context and the procedures followed in data collection. For our own purposes we might be interested in data from subhumid to hyperarid regions, but coverage of all, climates, including cold and wet ones, would make such a fund of information useful to a wider audience. publicize such a data bank. forms in the northern Great Basin (presently arid) give more than just hints that they were once subject Likewise, the effects of hurricane precipitation in a humid, deforested environment might shed light on the effects of torrential downpours in a desert setting, where a geomorphologist is rarely on the scene during the crucial hours (which are often at night).

A specific example illustrating the value of such a data bank is the work of one of our graduate students in the Forestry Department. He has just completed a superb dissertation on talus processes in the Venezuelan Andes. It contains many original conclusions based on voluminous data collected under very trying conditions. information will be dribbled out in publications over the years, but interested persons should know about this work now, and have access to it as a unit. We need a more organized system for learning about such research that is pertinent both to present deserts and to features formed during less arid interludes in desert regions.

Perhaps the USGS could organize and

to cryergic To understand the

(periglacial)

processes.

Perhaps the indica tors of climate and climatic change, collaborative studies between earth, hydrologic, and atmospheric scientists are required. The validity of geologic indicators of climatic change must first be judged in terms of how well they reflect changes in surficial processes and, in turn, how well process changes reflect changes in meteorologic and hydrologic variables. Also, process changes induced by climatic change must be differentiated from those induced by nonclimatic factors; the two types can easily be con fused in the geologic record.

U.S. Geological Survey, Menlo Park, Calif.

investigations of present and past climate variability and its causes and products, we should give attention to the present condition of our arid lands and their limits in providing for everincreasing human demands. We should examine the rates of human consumption of land and water; the primary and secondary effects of massive changes in runoff patterns and in composition of air and water; the changes in local climate; the spread of diseases endemic in arid soils, and the loss and replacement of native plant and animal species resulting from urbanization, agriculture, mining, energy production, silviculture, road building, recreation, military activities, and waste disposal. Such studies are not necessarily on the cutting edge of earth science, and generally do not require expensive or sophisticated monitoring devices. Yet, even very short term responses to human-induced changes in natural states of equilibrium can yield important information on the character and rates of geomorphic processes; thus they can support investigations of past events for which the geologic record is incomplete. Specific subjects for study are:

1. Past disturbances in a large variety of climatelandform-soil-vegetative assess processes of natural recovery and indirect consequences that may affect the human environment, and to provide a basis for planning future uses to minimize adverse effects. Study areas should include abandoned urban sites (mining towns and, if feasible, archeological sites); agricultural land; military and recreational sites; logged lands and those deforested for range conversion; overgrazed rangelands; and waste-disposal sites.

The effectiveness of rehabilitation and reclamation efforts. include mined sites (such as Black Mesa, northeast of Flagstaff, Arizona), utility corridors, rangeland, and farmland. Human Factors in Arid Lands

addition to supporting scientific

3. Urban effects on runoff, composition of air and
4. Rates whereby the products of historic natural

water, and local climate.

events, such as debris flows, floods, and fire, are modified.

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