A Workshop on Desert Processes, 

September 24-28, 1984-

Report on the Conference 

A Workshop on Desert Processes, 

September 24-28, 1984-

Report on the Conference 

By John F. McCauley and Jack N. Rinker 

U.S. GEOLOGICAL SURVEY CIRCULAR 989 

1 9 8 7 
Department of the Interior 

DONALD PAUL HODEL, Secretary 

U.S. Geological Survey 

Dallas L. Peck, Director 

Library of Congress Cataloging-in-Publication Data 

Workshop on Desert Processes (1984 : Flagstaff, Ariz.) 

A Workshop on Desert Processes, September 24-28, 1984--

Report on the Conference. 

U.S. Geological Survey Circular 989. 

Includes bibliography. 

Supt. of Docs. No.: I 19.4/2:989. 

1. Deserts--Congresses. 2. Arid regions--Remote 

sensing--Congresses. 3. Paleoclimatology--Congresses. 

I. McCauley, John F. II. Rinker, J.N. III. Title. 

IV. Series. 

GB11.W73 1984 551.4 86-600394 

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 
CONTENTS 

Page 

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 

Monitoring desert winds, by J.F. McCauley, C.S. Breed, 

P.J. Helm, G.H. Billingsley, and D.J. MacKinnon ...•...•••.•...••••.•• 6 

Key factors in arid-land monitoring efforts, by E.L. Skidmore .....•.....•. 9 

Recommendations for measurements and expanded instrumentation 

at the USGS Geomet sites, by Dale Gillette •...........•............ 10 

Soil-moisture measurement, by G.I. Smith ...•.••........•.....•.•..... 12 

Instrumented field sites, by Jack N. Rinker .....•...................•.. 12 

Characterization of vegetation and other nonerodible elements, 

by Melvin Satterwhite ......•••••...•.•.•••.........•.........•.• 13 

Military aspects of desert processes, by Ponder Henley ..•..•..•••....... 14 

Influence of chemical weathering, by Judy Ehlen .••••••••.••..••••••••• 14 

Heat-balance investigations, by Melvin Marcus ..•......•......•........ 15 

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

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 

References cited ........••••••.••..••••••••••.••••.•••..••••••.••.•.••.. 19 

Participants in Desert Processes Workshop ••••••.••..••...•••••....••..•.••.. 20 

ILLUSTRATIONS 

Figure 1. Map of western North America showing regional context 

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

2. Mosaic of Landsat images showing features of Great Basin 

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

3. Oblique high-altitude aerial view of parts of desert 

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

4. Photographs showing two key localities that illustrate 

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

5. Location map of USGS Geomet station sites in 

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

6. Photographs showing instrumentation at Gold Spring 

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

TABLE 

Table 1. Techniques and standards for measurements at Geomet 

sites ••.••.••..•••....••••.•••..•.••..••.•....•....•••••••• 11 

III 

A Workshop on Desert Processes, 

September 24-28, 1984-

Report on the Conference 

By John F. McCauley and Jack N. Rinker 1 

INTRODUCTION 

During the last decade, desert research has 

seen renewed emphasis as a result of satellite data. 

improved physical access, military considerations, 

and economic concerns such as regional 

desertification and overuse of ground-water 

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 to study the regional 

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). 

At present. the USGS is monitoring 

geometeorological conditions in different types of 

deserts in Arizona, using data relayed by satellite 

from solar-powered "Geomet" stations (McCauley 

and others, 1984). These stations consist of 

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 

1u.s. Army Engineer Topographic Laboratories, 

Fort Belvoir, Virginia 22060. 

1 

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 

discussion about selected topics. The individual 

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-
~Mojave 

Q Sonoran Desert :. 

[!:TI Chihuahuan Desert 

FIGURE 1.--Regional context of Arizona deserts 

and area of field trip (outlined) in Great Basin 

Desert (from Sheridan, 1981). 

introduction to the group, followed by discussion. 

Two days were then devoted to the field trips. 

consisting of a flyover of the Little Colorado River 

Valley, Moenkopi Plateau, Monument Valley. and 

parts of the Colorado River (figs. 2, 3). followed by 

ground traverses on the Moenkopi Pia teau and along 

the east side of the Little Colorado River Valley 

(fig. 4). The field trips provided a reconnaissance of 

the great variety of land forms that have developed 

from the interplay of desert processes operating on 

different types of surface materials under past and 

present climatic conditions in northeastern 

Arizona. The trips served as an introduction to 

discussion of desert processes--unsolved problems. 

current methods of study. and promising directions 

for new research. 

Topical discussions related to methods of data 

collection and interpretation followed the field 

trips; these sessions emphasized desert geomorphic 

processes in general, analogs in other parts of the 

world, vegetation, catastrophic events (droughts, 

windstorms, dust storms, floods), seasonal events, 

and climate change. The final day's summary 

session was a round-table discussion of problems and 

directions of future desert research, priorities. 

methods, strategies_, new tools, and the need for 

additional observation stations. Key questions 

addressed during these discussions, with 

recommendations for cooperative efforts. are 

incorporated in the following section of this 

document to provide guidelines for future research. 

2 

Acknowledgments 

The workshop was a cooperative effort of the 

USGS and ETL-CRS. We would particularly like to 

thank the following people. William J. Breed, 

Flagstaff, coordinated all workshop activities, 

prepared a guidebook to the localities visited, and 

led the ground portions of the field trip with Carol 

S. Breed, George H. Billingsley, and Paula Helm, 

USGS. Phyllis Corl, ETL-CRS, coordinated the 

advance planning at ETL-CRS for the workshop, and 

assisted in the preparation of aerial photo mosaics 

that were provided to each participant to illustrate 

the field areas. 

OBJECTIVES AND RECOMMENDATIONS OF THE 

DESERT WORKSHOP 

Part 1: Summary of Discussions 

The two goals of the workshop were (1) to 

determine the practical limits of knowledge and 

understanding of surface geometeorological 

processes in deserts, and (2) to provide a basis for 

encouraging discussion between scientists of 

different disciplines. These goals were met. During 

the conference, several key questions were 

addressed; these questions, and the consensus of the 

participants, were as follows: 

1. Have we an acknowledged understanding of cause 

and effect and kinetics regarding landform 

development and surface characterization in 

relation to desert processes (eolian. fluvial. 

mass-wasting, weathering)? 

Consensus: No. The interactions among 

materials, vegetation, wind, water, weathering. 

and mass wasting that produce various types of 

landforms and surface characteristics are not 

well understood, particularly in regard to the 

rates of these processes. More research is 

needed. both to understand better the presentday causes and effects and to interpret more 

precisely the geologic record. More emphasis 

should be placed on study of the boundary layer. 

which is where surface geologic processes 

develop and modify landscapes. Measurements 

of weathering and erosion rates should be 

increased. new techniques for measurement 

should be developed, and research on individual 

components of surface processes should be 

encouraged. 

2. Are more field observations and experimental 

measurements needed, or are existing models 

adeguate? 

Consensus: Field observations and theoretical 

modeling studies are needed at all levels of 

endeavor. and long-range experiments should be 
FIGURE 2.--Mosaic of Landsat images showing features of Great Basin Desert in northeastern Arizona. 

3 
started that will continue beyond our lifetimes 

to serve as a data base for future generations. 

The models discussed in this workshop refer to 

wind erosion and associated factors. Although 

the best available, these models are more 

suggestive than absolute and are restricted in 

scope. Additional field measurements and 

observations are needed that can best be 

supplied by cooperative interagency efforts. 

3. Are measurements needed such as those collected 

at the USGS Geomet stations? If so, are they 

adequate, or should they be expanded? 

Consensus: The measurements are needed. not 

only to improve basic understanding of eolian 

processes. but also to help in the development 

and testing of mathematical models. Existing 

instrumentation nets should be expanded. and 

FIGURE 3.--0blique high-altitude aerial view of parts of desert covered by field trip. View northeast 

across valley of Little Colorado River to Monument Valley on Arizona-Utah border (fig. 2). Two-day 

field trip included air and ground visits to key localities (fig. 4). 

4 
actual surface conditions should be better 

defined. For example, systematic measurements 

should be made over long periods at selected 

localities around each Geomet site to determine 

rates of weathering and erosion of the mapped 

bedrock and surficial units. Wind profiles should 

be constructed in downwind and crosswind 

directions, and related to the calculated erosion 

potential of measured winds, to help 

characterize the susceptibility of various 

surfaces to erosion. The vegetative elements of 

each site should be mapped to provide, as a 

minimum, estimates of cover (in percent) of four 

elements: (1) algae, lichen, and mosses, (2) 

herbaceous plants (grasses and herbs), (3) shrubs, 

and (4) trees; height and seasonal components 

should be addressed, as well as vegetative 

structure. 

4. If the Geomet types of measurement are to be 

expanded, what are the minimum and ideal 

requirements with respect to instrumentation. 

site arrangement, and site locations? 

Consensus: Minimum and ideal requirements 

were agreed upon and are reported in this 

document by Gillette and Skidmore. The 

instrumentation, starting at the Gold Spring site, 

should be increased both laterally and vertically 

and probably should include sensors for solar 

radiation. At the Gold Spring site , the USGS is 

trying to measure the sediment load of the air in 

relation to wind speed and direction. Although 

experimental, such measurements are critical to 

any understanding of erosional processes. These 

efforts should be expanded, and other sedimentmeasuring devices developed and tested. 

The USGS Geomet sites in Arizona's arid lands 

(figs. 5, 6) and the ETL-CRS instrumented test site 

in Virginia are the only places known to us where 

continuous, around-the-clock measurements are 

being collected of radiometric, meteorological, 

vegetation, and soil variables, and where 

temperature and moisture profiles are produced. 

Instrumentation and data collection at the two sites 

are similar, except that sediment flux is measured 

only at the Geomet station #1 (Gold Spring), and 

radiometric measurements in the two infrared 

imaging bands are made only at the ETL-CRS site. 

The models developed and tested by CRS for 

predicting time-varying thermal signatures and 

target-to-background thermal contrast are for a 

relatively moist, temperate region (eastern 

Virginia). At least one subhumid site should be fully 

instrumented so that its data can be compared with 

the CRS measurements and used to extend the 

predictive model to desert areas. The proposed 

Jornada collaborative site near White Sands, N. 

Mex., would be excellent for this purpose. 

5 

FIGU]:{E 4.--Among the localities that stimulated 

most discussion were (top) the Geomet site near 

Gold Spring on the Moenkopi Plateau, where 

sensors on two stations were being cross 

calibrated and prototype flux sensors tested, and 

(bottom) Red Rock Cliffs eroded in Moenave 

Formation of Triassic age in valley of the Little 

Colorado River (figs. 2, 3). 

Part II: Recommendations for Collaborative 

Research 

Several research tasks that would bene fit 

from cooperative efforts were identified and agreed 

to, pending availability of resources and permission 

from parent agencies. These were: 

1. The USGS and ETL-CRS will collaborate on 

collection of data at the Geomet sites (see 

McCauley and others, this volume). To provide 

the more complete surface descriptors needed 

for the models, ETL-CRS will map vegetation 

at the Geomet sites. Work was to start in 

fiscal 1985 at the Gold Spring site and continue 
as travel funds permit. 

2. The USGS and the State Climatology Laboratory, 

Arizona State University (Marcus, this volume), 

will exchange data for research use on an 

informal basis. 

3. The USGS and ETL-CRS will collaborate on site 

layout, expansion, and instrumentation of the 

Gold Spring Geomet site. E.L. Skidmore, U.S. 

Department of Agriculture (USDA) Wind 

Erosion Laboratory, and D.A. Gillette, National 

Oceanic and Atmospheric Administration 

(NOAA) will provide expertise and may loan 

equipment for sampling airborne dust. (See 

Skidmore, this volume, and Gillette, this 

volume.) ETL-CRS will provide soil heat-flux 

sensors and help evaluate soil-moisture 

measuring techniques. 

4. D.A. Gillette (NOAA) and ETL-CRS will collaborate on correlating ground measurements with 

pattern indicators on aerial photographs, to 

develop a procedure for estimating dust 

potential by image analysis. 

5. The USGS and ETL-CRS, in cooperation with 

USDA, Las Cruces, N. Mex., will collaborate on 

developing a Geomet station in an area 

representative of the Chihuahuan Desert in 

New Mexico (fig. 1). CRS will install 

instrumentation analogous to the ETL-CRS 

instrumented test site at Fort Belvoir, Va., and 

will assist in mapping the vegetation. The 

Jornada Experimental Range of the 

Agricultural Research Service, USDA, was 

proposed by E.L. Skidmore (USDA) and 

accepted as a candidate for collaborative 

efforts. The range is in a protected area on 

public land west of White Sands National 

Monument, New Mexico. It is the site of 

ongoing wind-erosion research by USDA 

personnel, who have acquired data there for 50 

years. The Jornada area is contiguous with an 

area mapped in detail by the the Desert Project 

of the U.S. Soil Conservation Service (Gile and 

others, 1981). It has been the site for studies 

of spectral reflectance indexes derived from 

Landsat data for use in monitoring changes in 

vegetation type and distribution (Musick, 

1984). Beginning in 1986, the Jornada area will 

be intensively monitored for surface changes 

due to eolian processes, using Landsat and 

other remotely sensed data, as part of NASA's 

Interdisciplinary Research Program in Earth 

Science (C.S. Breed, H.B. Musick and others, 

USGS, Flagstaff). 

6. ETL-CRS will provide all workshop participants 

with a list of references on chemical 

weathering in granites, and will provide future 

updates. 

7. A strong interest was expressed in the activities 

of the Army Research Office (ARO), and some 

research proposals from the workshop 

participants are likely to be submitted to that 

agency in the future. 

6 

CONTRIBUTIONS FROM WORKSHOP 

PARTICIPANTS 

Part 1: Monitoring of Processes in 

Arid F.nvironments 

Monitoring Desert Winds 

J.F. McCauley, C.S. Breed, P.J. Helm, 

G.H. Billingsley, and D.J. MacKinnon 

U.S. Geological Survey, Flagstaff, Ariz. 

Studies of geologic processes that affect 

desert surfaces have been severely handicapped by a 

lack of detailed data on meteorological 

characteristics, particularly on the intensity and 

periodicity of peak-gust wind speeds. The need of a 

quantitative data base for assessing rates of wind 

erosion became apparent during studies of arid 

regions on Earth that are considered analogous to 

certain surfaces on Mars. As a result of this need, 

in 1979 the USGS initiated a long-term study of the 

geologic role of wind relative to other processes, 

adapting the techniques of remote monitoring 

pioneered in studies of water resources to studies of 

desert processes. Detailed field measurements of 

geometeorological conditions are currently being 

obtained in several different desert environments of 

Arizona (fig. 5). The goa 1 is to establish and 

compare rates of change of natural desert surfaces 

by eolian processes under given geometeorological 

conditions, and thus to provide some of the longterm basic data needed to assess the effectiveness 

of wind as a geologic agent. 

Measurements of wind speeds (including peak 

gusts), wind directions, air temperature, humidity, 

barometric pressure, soil temperature, and 

precipitation are taken at 1-second intervals and 

recorded as 6-minute averages around the clock, by 

nonattended, solar-powered Geomet stations (fig. 

6). These stations are data-collection platforms 

coupled with an array of off-the-shelf 

meteorological and geological devices. The data 

are automatically transmitted in real time by GOES 

satellite and converted to graphic form for analysis 

by USGS scientists. Since the first station was 

deployed in 19 79, various problems in the system 

have been largely overcome, and Geomet stations 

are now operating at four sites in Arizona: Gold 

Spring, in the Great Basin Desert on the Navajo 

Indian Reservation; at Desert Wells (near Vicksburg) 

in the Upper Sonoran (Gila) Desert west of Phoenix; 

at Yuma, in the Lower Sonoran Desert near the 

Mexican border; and near Red Lake, on the east 

edge of the Mojave Desert (fig. 5). A fifth station 

soon will be deployed in New Mexico, in an area 

representative of the Chihuahuan Desert (fig. 1); 

the Jornada Experimental Range has been selected 

for this purpose. 

Each Geomet station was positioned after 

extensive site studies, which included detailed 
N -7----r 112° 

\ ... 

................... I 

Chinle _J 

36" I 

I 

I 

l 

I 

I 

3~~ 0 40 80km 

0 25 50mi 

FIGURE 5.--Location map of USGS Geomet station sites in Arizona deserts: A, Gold Spring; B, Desert 

Wells; C, Yuma Desert; and D, Red Lake. Precipitation isohyets outline shaded areas that receive 100 

mm or less (dark shading), 100 to 200 mm (intermediate shading), and 200 to 250 mm (light shading) 

average annual precipitation. Rose diagrams at Winslow and Yuma are circular histograms that 

indicate the theoretical sand moving capacity of winds, based on standard weather station records; 

arrows indicate calculated annual resultant directions of potential sediment transport by winds (from 

Breed and others, 1984). 

7 
geologic mapping and sampling of the surficial units 

(dunes, sand sheets, playas, channel deposits of 

ephemeral streams, and alluvial plains). Repeat 

photography from camera stations established at 

each site provides long-term documentation of 

physical changes and their relations to the 

monitored conditions. Vegetation is being surveyed 

at all sites in cooperation with ETL-CRS. In 

addition, effects of eolian processes on surface 

properties (including vegetation) will be monitored 

at the Yuma and Jornada sites, using aircraft, 

Landsat and other satellite remote-sensing data, in 

cooperation with NASA's Interdisciplinary Research 

Program in Earth Science. 

In early 1984, a second-generation station at 

Gold Spring was deployed that has specially 

modified sensors to measure dust and sand flux (fig. 

6). The dust sensor is a commercially available 

ANTENNA 

to GOES 

0 ~· 

..... ii"'liiQ 

FIGURE 6.--Solar-powered, remote-relay Geomet station with (A) sand-flux and (B) dust-flux sensors 

deployed near Gold Spring, northeastern Arizona. Sand-flux sensor initially in use had tipping-bucket 

mechanism (details, upper right), which proved to be too sensitive for field use, and has recently been 

replaced by a piezoelectric load cell. Dust-flux sensor housed in box (B) is shown in lower right. 

8 
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. These sensors are automated to 

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. Differences between the 

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. These two prototype sampling 

instruments directly measure some elements of 

sediment transport during the real-time wind 

erosion process. Suggestions were made in the 

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. Thus we are 

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 

E.L. Skidmore 

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

Manhattan, Kans. 

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. Any measurement system 

requires constant vigilance to ensure that the 

numbers being stored represent the truth. Ideally, 

measurements at the USGS Geomet sites should be 

9 

sufficient to allow calculation of energy, water, and 

momentum balances. 

1. Energy balance.--The net solar energy 

received at the Earth's surface is distributed 

according to the function 

(1) 

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: 

(2) 

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. Momentum balance.--Vertical transfer of 

horizontal momentum to the surface can be 

estimated from measurements of friction velocities: 

(3) 

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: 

u* z-d U k [ln(-2 -) + 4l] (4) 

z 0 

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: 

R 

i 

g 

ez - el 

e (u,- u,) 2 

zz - zl 

where g is acceleration 

temperature, and 

(5) 

of gravity, e is potential 

temperature and wind-speed gradients, respectively. 
In order to monitor energy, water, and 

momentum fluxes more completely at the USGS 

Geomet stations, the following additional 

measurements are desirable: 

1. Wind speed, now measured at 6 m above the 

ground, should also be measured at about 1 m 

above the ground (about twice the height of the 

vegetation). Once the surface aerodynamics 

(z0 and d) have been characterized, the windspeed gradient obtained in this way would 

enable calculations of the friction velocity and 

hence the momentum flux. 

2. Air temperature should also be measured at an 

additional height. The existing air-temperature 

sensor and an additional one should be placed at 

the same heights suggested above for the two 

anemometers. Both air temperature and windspeed data are needed at two heights to 

measure air stability. Measurements of the 

humidity gradient (water-vapor pressure 

profile) can be used to calculate 

evapotranspiration by the Bowen ratio 

technique, but the needed accuracy is difficult 

to achieve because of instrumentation 

problems. 

3. Incoming and outgoing solar and net radiation 

should be measured for calculation of surface 

albedo. The albedo indicates whether the 

surface is wet, dry, or snow covered. Net 

radiation is important in considerations of 

energy and water balances. 

4. Water in the profile should be measured and 

modeled, because the activity of water 

influences many surface processes. 

5. The protection offered by the surface vegetation 

against wind erosion, and the partitioning of 

the momentum flux between the vegetation and 

the ground surface, should be characterized. 

Consult with the USDA's Wind Erosion 

Research Unit for their procedures and with 

Dale Gillette, NOAA. 

6. The displacement height and the roughness 

parameter of the log-profile law (equation 4) 

should be characterized for the surfaces at the 

Geomet stations. Those parameters change as 

vegetation character changes. 

7. The erodibility of the surface material in a dry 

state should be characterized. If the material 

is single grained, the erodibility is a function of 

grain-size distribution. If the material is 

aggregated into secondary particles, its 

erodibility is a function of aggregate-size 

distribution and aggregate stability. A 

consolidated or crustal surface represents 

another set of conditions even more complex. 

8. Lastly, the spatial sampling requirements of the 

sand- and dust-flux measurements (and others) 

should be evaluated. Is one getting samples 

sufficient to characterize the process as 

intended? 

10 

Recommendations for Measurements and Expanded 

Instrumentation at the USGS Geomet Sites 

Dale Gillette 

National Oceanic and Atmospheric 

Administration (NOAA), 

Boulder, Colo. 

Specific parameters to be measured (table 1): 

A. The characteristics to be measured (as 

related to existing wind-erosion equatio..ns) are: 

1. Dry-aggregate structure of the sediment. 

Related to the "I" factor of the USDA Wind 

Erosion Laboratory (WEL), and to the U*t 

(threshold friction velocity) of Gillette. This 

measurement is local and has a scale of a 

few square centimeters. 

2. Nonerodible-element distribution. Related to 

nonerodible elements of WEL and to Lc (ratio 

of silhouette area to erodible soil area) of 

Gillette. Nonerodible elements include 

vegetation cover (including algal mats) and 

rock cover. 

3. Wind. The probability distributions used for wind 

are either Rayleigh (one parameter), as with 

Gillette, or Weibull (two parameters), as with 

WEL. Actual empirical data from the 

Geomet stations would be best. The 

objective is to determine the momentum flux 

(F') at the ground surface. The first step is 

to measure the wind speed (U) or friction 

velocity (U*) above the vegetation canopy by 

(1) estimating the drag coefficient from the 

aerodynamic roughness of the canopy and 

measuring the wind speed well above canopy 

height, or (2) measuring the wind profile 

above the canopy. For neutrally stratified 

air, u* may be determined from 

u* 

U(z) = K Sl.n[(z-d)/z0 ] (1) 

Then the momentum flux F' may be 

determined as 

_2 I 

F' = p . CD U(F /F) a1r 

or p . u2 (F'/F) a1r 

(2) 

(3) 

where F is momentum flux above the canopy, 

_2 

F =Pair CD U anermrreter 

F'/F is related to Lc, CD is the drag 

coefficient, and p a iris air density. 

4. Fetch. Length of erodible material. Related to 

the term L of both WEL and Gillette. 

5. Soil moisture. Combined with wind in C factor 

of WEL; virtually neglected for sand surfaces 

by Gillette. The reduction of surface stress is 
TABLE 1. Techniques and standards for measurements at Geomet sites 

Parameter 

1. Dry-aggregate 

structure 

2. Nonerodibleelement 

distribution 

3. Wind 

4. Fetch 

5. Soil moisture 

6. Vegetation 

7. Sediment 

transport 

expressed as 

Minimum approach/equipment 

Measure percent mass 

greater than 0.84 or 1.00 

mm; crust thickness, 

hardness. Use mode of 

loose material 

Determine from visual 

observations and 

photographs 

Measure with one 

anemometer located well 

above surface-roughness 

elements 

Quantify from visual 

observations 

OVen-dry samples; 

correlate with 

precipitation by empirical 

methods; correlate with 

albedo, conductivity 

See no. 2 above 

For sand: creep 

collector, pie tins, 

drumcatcher, Bagnold 

catcher, textile bags, 

textile/Bagnold 

combination, fly paper 

For dust: petri dishes or 

marble; records dust 

settlement, not flux (mass 

concentration) 

Ideal approach 

Measure (a) full seive-size 

distribution of surface materials, (b) 

modulus of rupture (if greater than 1 

bar), and (c) thickness (if greater 1 

em, won't erode) 

Determine from digitized 

photographs, topographic 

maps, and Lc: 

silhouette area 

erodible area 

Add (a) stress plate at ground, or (b) 

microscale wind profile within 

roughness element, or (c) two to five 

anemometers above canopy 

Quantify by remote monitoring 

observations plus ground observations 

over time 

Need to develop 

See no. 2 above 

For sand: piezoelectric sensor with 

logarithmic amplification (Gillette, 

work in progress), or get signal from 

pressure transducer under bucket 

instead of tipping bucket; or (for 

about $60 million) an optical array 

probe (OAP) particle-measuring system 

(PMS), or visibility (mass 

concentration) meter, in which V =aM-l 

where M is mass concentration. 

Unfortunately, these systems depend on 

optical characteristics of the 

particles and are very vulnerable to 

damage in the field 

Automated particle counter as present 

on Geomet station #1. Fancier models 

are available with manifold intake for 

measuring at different levels and at 

different particle-size distributions; 

or electrostatic precipitators 

w 0.5 w (actual soil moisture) 

6. Vegetative cover. Equivalent to R of WEL, part 

of Lc of Gillette. 

7. Sediment transport. 

15 (potential moisture at 15 b pressure) 

and is measured in newtons/m2. 

11 

8. Ridge roughness (K). Can be ignored, as it is an 

insignificant influence on erosion of desert 

surfaces. 
B. What time scale is optimum for 

monitoring? The minimum acceptable period of 

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 co2 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. 

Soil-Moisture Measurement 

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

Menlo Park, Calif. 

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. The 

chemical activity of any water in vapor form is the 

ratio of the partial pressure of the water vapor in 

question (pH 0 ) to the partial pressure of vapor 2 

that is in equilibrium with pure water, under the 

same conditions of temperature and pressure 

(p* ~0) These ratios are numerically related, by 

definition, to the meteorologist's "relative 

humidity" (RH): 

PH 0 

--::-* 2 RH --- X 1 00 

PH 0 

2 

Therefore, when both liquid water 

coexist in a soil, if at equilibrium, 

and if the water is pure, 

PH 0 

2 -,.,---- = a * H20 

PH 0 

2 

and RH = 100 percent. 

(1) 

and its vapor 

(2) 

(3) 

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 0 , and (2) temperature at 

2 

a succession of horizons in a soil or rock. The 

values measured are the integrated effective 

chemical activity and temperature, as they pertain 

12 

to an ongoing chemical reaction, for the period of 

measurement. All chemical weathering involves 

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. The vials must be removed and 

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. 

Instrumented Field Sites 

Jack N. Rinker 

U.S. Army Engineer Topographic 

Laboratories, Center for Remote Sensing, 

Fort Belvoir, Va. 

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 of spectral and radiometric 

measurements. Over the years, many useful 

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, 
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. Our CRS research is directed 

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 soil-temperature profiles, airtemperature profiles, wind speed and direction, dew 

point, soil heat flux, incoming and outgoing 

radiation, and radiometric brightness (8-

14~m wavelength band). (A list of the instruments 

used at the CRS site is appended.) These 

measurements are the minimum that we need to 

understand the ever-changing thermal 

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 in wind erosion and associated 

characteristics of the airborne sediment load in 

relation to wind velocity, many of their 

measurements and instrumentation needs overlap 

those of ETL-CRS. The exceptions are their 

measurement of sediment load and our 

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 understand erosional and 

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 

13 

probably no longer representative of local 

conditions. The Gold Spring station has, in itself, 

induced turbulence and needs a "cleaner" 

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 involved in instrumentation, field 

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, 

Fort Belvoir, Va. 

(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 

Nonerodible Elements 

Melvin Satterwhite 

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. The vegetation can be described 

simplistically as: 
1. Mat-formers: algae, moss, lichen 

2. Herbaceous plants: grasses, herbs 

3. Woody plants: shrubs and trees 

This general scheme can be subdivided into very 

detailed classes at the species level. Classification 

systems have been developed for local, regional, 

continental, and global vegetation. 

As plants progress through their annual growth 

cycle, differences occur in the percentage of stems, 

branches, and leaves that make up the canopy. The 

seasonal cycle of active plant growth and dormant 

stages varies by species. Thus both the seasonal 

growth and the type of vegetation affect 

geomorphic processes in complex ways. 

Plant species are indicators of surface or 

near-surface substrate conditions, such as 

chemistry, moisture, and texture. These 

plant/factor associations must be ascertained from 

field investigation. The plant species' soil-binding 

versus soil-passing characteristics should be 

described. Some plants may allow the passage of 

windblown particulates, whereas others trap them. 

The latter type must survive partial burial either by 

rapid growth or by a specialized canopy whose lower 

part is a catching type and whose upper part is a 

passing type. The characteristics of the catchingand passing-type canopies, such as those of 

mesquite and ephedra, require study. Species such 

as mesquite can stabilize a surface because the 

plant can survive burial by means of adventitious 

root growth. Pro files in coppice dunes can 

document recent periods of dune stability and dune 

instability, but the time-rate sequence must be 

studied; for example, the height of the shrub crown 

above the soil surface and the presence of litter 

beneath are indicators of present-day stability. 

In wind-erosion equations, the vegetative 

roughness factor summarizes several vegetative 

parameters, but different plant parts (leaves, 

flexible stems, and rigid stems or branches) may 

have different roughness values. In order to 

characterize a given locality, a roughness value 

must summarize all values for a physiognomic class, 

vegetation type, or plant community. 

Vegetation can be readily described by using 

large- to medium-scale aerial photography in 

association with conventional phytosociological 

sampling procedures. Satellite imagery can be used 

for general regional vegetation investigations, by 

association of the various image patterns with 

different plant communities. Numerous techniques 

are available for describing the vegetation within 

map units of an image. 

Factors that affect the erodibility of 

inorganic surface materials should also be studied: 

the distribution of salt crusts (powdered or 

indurated), of granular surfaces (gravel and cobbles 

or sand, silt, or clay particles), of bedrock, moisture 

levels, and surface soil structure (granular or 

vesicular). Several of these surface characteristics 

can occur in combination and can vary within very 

short distances in arid and semiarid regions. 

14 

Military Aspects of Desert Processes 

Ponder Henley 

U.S. Army Engineer Topographic Laboratories 

Center for Remote Sensing, Fort Belvoir, Va. 

The military significance of terrain is well 

known, and the ability to predict terrain conditions 

and their effects on military operations is a national 

necessity. The use of increasingly delicate and 

sensitive equipment in the modern battlefield 

environment requires an increased ability to predict 

and measure surface and atmospheric conditions. 

Dust generated by vehicles, by wind, and by 

explosions affects visual and electro-optical 

visibility and performance of equipment. The 

predictability of potential dust hazards by field and 

remote-sensing methods is thus of great interest to 

the Army, and cooperative work toward this goal 

with NOAA, USDA, and USGS is desirable. NOAA 

is modeling and measuring the effect and character 

of atmospheric dust; USDA is working with 

problems of soil erosion by wind and methods to 

predict and prevent soil removal; the USGS is 

examining processes that shape desert surfaces; and 

the Army is looking for ways to predict, by remotesensing techniques and interpretation, areas that 

produce dust due to military operations. 

Through cooperative efforts by these 

agencies, some problems can be lessened. The use 

of remote sensing to characterize the surface 

(source materials, wind regimes, nonerodible 

elements, and soil moisture), coupled with the winderosion and dust-production formulas developed by 

NOAA and USDA, may allow some prediction of 

dust potential in a given area. Research is needed 

in the methods used to characterize nonerodible 

elements of the surface (vegetation,. soil crusts, 

gravel veneers, and moisture). The remote-sensing 

research should include photointerpretation 

techniques and spectral measurements to 

characterize the various elements that could be 

used as indicators of surface conditions. 

Influence of Chemical Weathering 

Judy Ehlen 

U.S. Army Engineer Topographic Laboratories 

Center for Remote Sensing, Fort Belvoir, Va. 

The effects of wind erosion have generally 

been considered secondary to effects of water, even 

in desert environmen~s. Although wind has 

obviously played a significant role in forming desert 

landscapes, many desert landforms and surface 

textures may be relict from past humid climates. 

The effects of even slightly more water than 

presently available in arid lands probably played a 

major role in forming these features. For example, 

pans and tafoni (honeycomb weathering) probably 

were originally formed by cheTl)ical weathering and 
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. 

Heat-Balance Investigations 

Melvin Marcus 

Laboratory of Climatology/Department of 

Geography, Arizona State University, 

Tempe, Ariz. 

The establishment of the USGS Geomet 

network is an important beginning in understanding 

desert processes at the earth-atmosphere 

interface. Climatic investigations in three areas 

can enhance the current effort: (1) increased 

measurement and determination of factors 

affecting air movement near the surface and 

transport of particles; (2) development of full heatbalance 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 and others, D.A. Gillette, and 

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. For example, short-wave and 

long-wave radiation fluxes react differently 

depending on such factors as surface material, soil 

moisture, and snow cover. These differences feed 

back through the weathering system and the 

15 

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 investigations should 

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. The Geomet desert stations 

provide an excellent opportunity to attempt to 

relate sets of highly localized data to ongoing 

longer term, synoptic weather patterns. Such 

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 validations of the 

imagery. Both the interface physical climatology 

and synoptic assessments discussed above provide 

excellent means to this end. 

Part II: Relevance to Paleoclimatic Studies 

General Statement 

Juergen Reinhardt 

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 
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 

indicators of several elements of climate. 

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 

16 

cycles are represented by variations in the lowlatitude sea-surface temperatures and Caco3 

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. 

Investigating Climate Change 

Stephen G. Wells 

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. In order to evaluate climatic effects 

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: 

Independent 

Time (geochronology) 

Geology (lithology, 

structure) 

Climate 

Tectonic relief 

Dependent 

Vegetation 

Total sediment 

yield 

Total discharge 

Morphology and 

other landform 

characteristics 

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. For example, the impact of 

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. 
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 KAr, 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? Comparing data for 

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: (1) the causes, types, magnitude, and 

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 (4) the interdependence of geologic, 

atmospheric, biologic, and hydrologic processes 

during an episode of climatic change. 

Geomorphologists have recently begun to 

understand and quantify the interdependence of 

modern systems, but these studies have not been 

truly interdisciplinary. As indica ted in this 

workshop, future studies should be interdisciplinary. 

Remarks on Desert Research and Data Sources 

Theodore Oberlander 

University of California, Berkeley, Calif. 

Research on desert processes could have two 

alternative goals: (1) to characterize and quantify 

the processes currently affecting desert 

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 

17 

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! To understand the 

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. Accordingly, 

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. Perhaps the USGS could organize and 

publicize such a data bank. For example, slope 

forms in the northern Great Basin (presently arid) 

give more than just hints that they were once 

subject to cryergic (periglacial) processes. 

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. Perhaps the 

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. 
General Comments 

Erhard Schulz 

University of Wiirzburg 

Wiirzburg, West Germany 

1. A prerequisite for continuing work in arid lands 

is to define the landscapes or environments in 

which the research or measurements are done, 

in order to ensure that correlations are made 

only between comparable environments. 

2. Time is an important factor in interpreting 

physical environments, which are only in part 

the results of present climatic conditions; many 

are relict and reflect processes that operated 

under different climatic conditions. 

3. Stable landscapes that have sufficient rainfall 

and permanent, diffuse vegetation, and which 

are formed by relatively uniform processes, are 

very different from unstable landscapes subject 

to catastropic events. "True" deserts seem to 

be stable environments, whereas many areas 

described as undergoing desertification are 

unstable. 

4. Desert climate is characterized not only by low 

precipitation and strong seasonality, but also by 

irregular and unpredictable rainfall in all 

seasons. 

5. "True" desert vegetation must undergo a great 

quantitative change before it changes in quality 

following eli rna tic fluctuations. 

Interpretation of Arid Landscapes: 

Some General Ideas for Future Research 

John C. Dohrenwend 

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

To achieve a comprehensive understanding of 

desert landscapes, much additional research is 

needed to answer the following questions: 

1. What processes operate in and on arid 

landscapes? · 

2. How do these processes interact and how are 

they interrelated? 

3. How sensitive are these processes to climatic 

change? What processes dominate under 

specified climatic conditions? 

4. At what rates have these various processes 

opera ted over time? For how long? In what 

sequence? 

To determine what processes are presently 

operating on the landscape, additional field-based 

measurement, monitoring, and analytical 

description of active processes are required. Some 

knowledge of the general geology of a region 

provides a useful framework for such investigations, 

but detailed information directly relevant to 

specific monitoring sites is essential to this work. 

The results of monitoring active processes cannot 

18 

be usefully applied to a general understanding of 

landscapes unless the geologic contexts of the 

monitoring sites and their immediate vicinities are 

thoroughly and precisely documented and analyzed. 

An understanding of the interrelations 

between processes can perhaps be best achieved 

through combining the measurement of active 

processes and the reconstruction of process changes 

through time as revealed from analyses of the 

surficial geologic record. Many feedback 

mechanisms of process-response operate much too 

slowly to be detectible by the monitoring of active 

processes. Yet it is these long-term interactions 

that are probably most important to the evolution 

of landscapes. Therefore, a complete understanding 

of landscapes requires knowledge of: (1) how 

processes operate and interact, and (2) how these 

processes and their interactions change through 

time. 

An understanding of what processes are 

dominant under what climatic conditions requires a 

very carefully planned and documented monitoring 

system involving the coordinated simultaneous 

measurement of multiple processes. Such an effort 

would require a substantial and very long term 

commitment of scientific resources. Even if such a 

comprehensive monitoring effort could be mounted 

and maintained, its results could not be realistically 

extrapolated to interpretations of landscapes 

without precise and detailed knowledge of the 

surficial geology of the monitoring sites. 

Detailed knowledge of process rates and the 

relative importance of various processes in the 

shaping of any landscape can be achieved only by a 

thorough and insightful analysis of the surficial 

geologic record. To interpret this record for 

analyses of the types, rates, periods, and sequences 

of processes responsible for the shaping of a given 

landscape, three factors are critical. We need 

precise and detailed time control for the late 

Cenozoic. We must identify reliable geomorphic 

and stratigraphic indicators of climate. We must 

correctly interpret these indicators relative to the 

types and magnitudes of processes and the 

directions and magnitudes of climatic change that 

they represent. 

With respect to the development of precise 

and detailed time control, the following general 

categories of research are required: (1) verification 

and calibration of both radiometric and relative 

age-dating techniques, primarily techniques such as 

rock-varnish chemistry, K-Ar dating of young 

volcanic rocks, secular paleomag~~tic {tf;riations, 

i2~ analyses of rare light isotopes ( Cl, Be, and 

I); and (2) identification of areas where precisely 

datable geologic phenomena are reliable indica tors 

of climate or process. Ideally, such studies should 

be conducted in areas where several dating methods 

can be cross-calibrated and where these calibrated 

methods can be directly applied to the study of arid 

processes and landforms. 

With respect to geomorphic and stratigraphic 
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. 

Human Factors in Arid Lands 

Howard Wilshire 

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

In addition to supporting scientific 

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 assemblages, to 

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. 

2. The effectiveness of rehabilitation and 

reclamation efforts. Study areas should 

include mined sites (such as Black Mesa, 

northeast of Flagstaff, Arizona), utility 

corridors, rangeland, and farmland. 

19 

3. Urban effects on runoff, composition of air and 

water, and local climate. 

4. Rates whereby the products of historic natural 

events, such as debris flows, floods, and fire, 

are modified. 

REFERENCES CITED 

Breed, C.S., Fryberger, S.G., Andrews, S., 

McCauley, C.K., Lennartz, F., Gebel, D., and 

Horstman, K., 1979, Regional studies of dunes 

in sand seas observed by remote sensing, 

Chap. K, in McKee, E.D. (ed.), A study of 

global sand seas: U.S. Geological Survey 

Professional Paper 1052, p. 305-397. 

Breed, C.S.,and Grow, T., 1979, Morphology and 

distribution of dunes in sand seas observed by 

remote sensing, Chap. J, in McKee, E.D. 

{ed.), A study of global sand seas: U.S. 

Geological Survey Professional Paper 1052, p. 

253-302. 

Breed, C.S., McCauley, J.F., Breed, W.J., 

McCauley, C.K., and Cotera, A.S., Jr., 1984, 

Eolian (wind-formed) landscapes, in Smiley, 

T.L., Nations, J.D., Pewe, T.L., and Schafer, 

J.P., eds., Landscapes of Arizona-The 

Geological Story: University Press, p. 359-

413. 

Gile, L.H., Hawley, J.W., and Grossman, R.B., 1981, 

Soils and geomorphology in the Basin and 

Range area of southern New MexicoGuidebook to the Desert Project: New Mexico 

Bureau of Mines and Mineral Resources, 

Memoir 39, 222 p. 

McCauley, J.F., Breed, C.S., Helm, P.J., Billingsley, 

G.H., MacKinnon, D.J., Grolier, M.J., and 

McCauley, C.K., 1984, Remote monitoring of 

processes that shape desert surfaces: The 

Desert Winds Project: U.S. Geological Survey 

Bulletin 1634, 19 p. 

McCauley, J.F., Breed, C.S., Schaber, G.G., 

McHugh, W.P., Issawi, B., Haynes, C. V., 

Grolier, M.J., and E1 Kilani, A., 1986, 

Paleodrainages of the Eastern Sahara--the 

radar rivers revisited (SIR-A/B implications 

for a mid-Tertiary Trans-African drainage 

system): IEEE Transactions, Geoscience and 

Remote Sensing, v. GE-24, no. 4, p. 624-648. 

McCauley, J.F., Schaber, G.G., Breed, C.S., Haynes, 

C. V., Grolier, M.J., Issawi, B., Elachi, C., and 

Blom, R., 1982, Subsurface valleys and 

geoarchaeology of Egypt and Sudan revealed 

by Shuttle Radar: Science, v. 218, no. 4576, p. 

1004-1020. 

Musick, H. B., 1984, Assessment of Landsat 

Multispectral Scanner spectral indexes for 

monitoring arid rangeland: IEEE Transactions, 

Geoscience and Remote Sensing, v. GE-22, p. 

512-519. 
Schumm, S.A., and Lichty, R. W., 1965, Time, space, 

and causality in geomorphology: American 

Journal of Science, v. 263, p. 110-119. 

Sheridan, David, 1981, Desertification of the United 

States: Washington, U.S. Council on 

Environmental Quality, 142 p. 

PARTICIPANTS IN DESERT PROCESSES WORKSHOP 

Sue Beard 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

George Billingsley 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

Carol Breed 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

William Breed 

1456 Meade Lane 

Flagstaff, Arizona 86001 

John C. Dohrenwend 

U.S. Geological Survey 

345 Middlefield Road, MS 941 

Menlo Park, California 94025 

Judy Ehlen 

U.S. Army Engineer Topographic Laboratories 

Center for Remote Sensing 

Fort Belvoir, Virginia 22060-5546 

Dale Gillette 

R/E/ AR 4, National Oceanic and 

Atmospheric Administration 

325 Broadway 

Boulder, Colorado 80303 

Maurice Grolier 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

Paula Helm 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

Ponder Henley 

U.S. Army Engineer Topographic 

Laboratories 

Center for Remote Sensing 

Fort Belvoir, Virginia 22060-5546 

Guo Huadong 

Department of Research Development 

National Remote Sensing Center 

Beijing, People's Republic of China 

20 

Eric Karlstrom 

Department of Geography 

Northern Arizona University 

Flagstaff, Arizona 86003 

David J. MacKinnon 

U.S. Geological Survey 

Flagstaff, Arizona 86001 

Melvin G. Marcus 

Department of Geography 

State Climatology Laboratory 

Arizona State University 

Tempe, Arizona 85281 

John F. McCauley 

U.S. Geological Survey 

Flagstaff, Arizona 85281 

Dorian Mills 

Leigh ton and Associates 

4393 Viewridge Ave., Suite D 

San Diego, California 92123-1619 

Theodore Oberlander 

Department of Geography 

University of California 

Berkeley, California 94720 

Juergen Reinhardt 

U.S. Geological Survey, MS 908 

Reston, Virginia 2 209 2 

Jack N. Rinker 

U.S. Army Engineer Topographic 

Center for Remote Sensing 

Fort Belvoir, Virginia 22060-5546 

Melvin Satterwhite 

U.S. Army Engineer Topographic 

Laboratories 

Center for Remote Sensing 

Fort Belvoir, Virginia 22060-5546 

Gerald G. Schaber 

Chief, Branch of Astrogeology 

U.S. Geological Survey 

Flagstaff, Arizona 86001 
Erhard Schulz 

Geographisches lnstitut 

University of Wiirzburg 

Wiirzburg, West Germany 

Edward L. Skidmore 

U.S. Department of Agriculture 

Wind Erosion Laboratory 

Room 204, E. Waters Hall 

Kansas State University 

Manhattan, Kansas 66506 

George I. Smith 

U.S. Geological Survey 

345 Middlefield Road, MS 902 

Menlo Park, California 94025 

21 

Stephen G. Wells 

Department of Geology 

University of New Mexico 

Albuquerque, New Mexico 87131 

John Whitney 

U.S. Geological Survey 

Box 25046, DFC, MS 913 

Denver, Colorado 802 25 

Howard Wilshire 

U.S. Geological Survey MS 7 5 

345 Middlefield Road 

Menlo Park, California 94025 
GPO 785-048/48024