Application of Landsat Products 

in Range- and Water-Management 

Problems in the Sahelian Zone 

of Mali, Upper Volta, and Niger

Prepared on behalf of the Office 

of Science and Technology, 

Agency for International Development, 

U.S. Department of State

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058
Application of Landsat Products 

in Range- and Water-Management 

Problems in the Sahelian Zone 

of Mali, Upper Volta, and Niger

By M. E. COOLEY and R. M. TURNER

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058

Prepared on behalf of the Office 

of Science and Technology, 

Agency for International Development, 

U.S. Department of State

Landsat imagery can aid 

in solving problems 

related to natural phenomena 

and human activity

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1982
UNITED STATES DEPARTMENT OF THE INTERIOR 

JAMES G. WATT, Secretary

GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Cooley, Maurice E.

Application of Landsat products in range- and water-management problems in the Sahelian Zone of Mali, 

Upper Volta, and Niger.

(Geological Survey professional paper; 1058) 

Bibliography: p.

1. Range management—Remote sensing. 2. Range management—Sahel. 3. Remote sensing—Sahel. 4. Watershed management—Remote sensing. 5. Watershed management—Sahel. 6. Landsat satellites. 7. Sahel. 

I. Turner, Raymond M., joint author. II. United States. Agency for International Development. Office of Science 

and Technology. III. Title. IV. Series: United States.

Geological Survey. Professional Paper; 1058. 

SF85.6.R45C66 333.7 78-25686

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304
CONTENTS Page

Abstract ________________________________________________________________ 1

Introduction ______________________________________________________________ 1

Acknowledgments ________________________________________________________ 2

General procedure ________________________________________________________ 3

Onsite investigation ___________________________________________________— 3

Selection of imagery _______________________________________________————— 4

Geohydrologic setting_________________________________________________________ 4

Savanna vegetation __________________________________________________________ 5

Landsat imagery in relation to range and water assessments ________________________________——— 11

River-blindness control ________________________________________________————— 13

Tse-tse fly control ________________________________________________________ 15

Bush-burning monitoring ____________________,_______________________________ 16

Factors affecting the availability of arable land ______________________________________— 19

Alluvial flats and small valleys ____________________________________________——— 19

Channel and flood-plain alluvium along the Niger River ____________________________————— 23

Laterite duricrusts _____________________________________________———————— 24

Accelerated erosion _______________________________________________________ 25

Annual flood of the Niger River _________________________________________________ 27

Ground-water development in fractured rocks __________________________________________ 28

Evaluation and utilization of Landsat imagery ______________________________________—————— 29

Landsat imagery with explanations _________________________________________________ 32

References cited ____________________________________________________________ 52

ILLUSTRATIONS Pa^

FIGURE 1. Map of the Liptako-Gourma Authority region and adjacent area in Mali, Niger, and Upper Volta showing principal

physical features and localities visited during onsite inspections _________________——————— 2

2. Mean annual precipitation, in millimeters, in parts of Mali, Niger, and Upper Volta (taken from Archambault,

1960, fig. 2) _____________________________________________________ 5

3. Vegetation zones in parts of Mali, Niger, and Upper Volta (taken from Keay, 1959) __________________ 8

4. Photographs taken along the White Volta River showing influence of man's activities on vegetation and terrain __ 9

5. Photograph showing west side of the Niger River valley near Niamey, Niger _____________________ 12

6. Photographs showing effects of man's activities around small villages ________________________ 13

7. Photograph of the White Volta River east of Ouagadougou, Upper Volta _______________________ 16

8. Photograph of unattended unchecked brush fire northwest of Bamako, Mali, April 24,1974 _____________ 17

9. Diagramatic sections of small valleys near Ouagadougou, Upper Volta, and Niamey, Niger, showing distribution

of laterite, alluvial deposits, areas of accelerated erosion, vegetation, and ground-water conditions __________ 18

10. Photograph of a profile of the gray alluvium exposed in a steep-sided channel near Bamako, Mali _________ 19

11. Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution

of laterite, alluvial deposits, terraces, and vegetation zones ____________————————————— 20

12. Photograph of small bucket-irrigated vegetable gardens along the bank of the Niger River at Niamey, Niger ________ 24

13. Photographs of laterite in road cuts near Bamako, Mali ______________________________— 25

14. Photographs showing accelerated erosion in Mali and Upper Volta ____________________—————— 26

15. Low-altitude oblique aerial photograph showing fractures, indicated by arrows, in the Gres Ordovicien (Ordovician sandstone) near the Baoule River northwest of Bamako, Mali ____——————————————————— 29

16. Diagrammatic cross section of Dallol Bosso near Niamey, Niger _______________________———— 30

17. Index map showing the areas represented by the six selected Landsat frames in Mali, Niger, and Upper Volta that

are evaluated in this report _____________________________________________ 32 

Landsat Frames:

S-1. False-color composite Landsat image (MSS bands 4, 5, and 7 of 1117-10232, November 17,1972) of the region

near Bamako, Mali __________________________________________________ 33 

S-2. False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095-10000, October 28,1972 near Ouagadougou,

Upper Volta _____________________________________________________ 36 

S-3. False color composite (MSS bands 4, 5, and 7 of Landsat image 1262-10290, April 11,1973) of the Baoule River

region northwest of Bamako, Mali _________________________——————————————— 42 

S-4. False color composite (MSS bands 4, 5, and 7 of Landsat image 1111-09483, November 11,1972) of the region near

Tillabery, Niger __________________________________________———————— 44 

S-5. Part of Landsat frame 1110-09424, MSS band 5, showing alluvial deposits of the Dallol Bosso and the Niger River

valley near Niamey, Niger __________________________________________——— 46 

S-6. False color composite Landsat image (MSS bands 4, 5, and 7 of 1079-10102, October 12,1972) showing part of the

Inland Delta of the Niger River nearTombouctou, Mali _____________———————————————— 48

TABLES Page

TABLE 1. Brief description of the stratigraphic units and their utilization by man in areas near Bamako, Mali, Niamey, Niger,

and Ouagadougou, Upper Volta _______________________————————————————— 6

2. Tentative assessment for relating Landsat imagery to selected problems in range and water problems in the LiptakoGourma countries___________________________________________—————— 14

3. Distribution of arable land and its relationship to accelerated erosion and gray alluvium _______——————— 22

4. Mean annual discharge at two gaging stations in the Niger River system, southern Mali ——————————————— 27

Application of Landsat Products in Range- and Water-Management Problems 

in the Sahelian Zone of Mali, Upper Volta, and Niger

By M. E. COOLEY and R. M. TURNER

ABSTRACT

A brief field investigation during April and May 1974 to 

evaluate the application of Landsat (formerly ERTS) imagery to 

range- and water-management problems in Mali, Upper Volta, 

and Niger shows that imagery can provide general overviews of 

regions or even entire countries, can be used in areas where 

few or no good ground surveys exist, can provide a basis for 

repetitive inventorying and monitoring transient environmental 

changes on the Earth's surface, and can aid in solving special 

problems of disease-vector control or human activity. Specific 

potential applications of Landsat imagery were identified in 

river-blindness control, tse-tse fly control, bush-burning evaluation, distinction of arable from nonarable lands, analysis of 

problems of accelerated erosion, and monitoring of the annual 

flood of the Niger River, and of ground-water development in 

fractured rocks.

Introduction

As increasing pressures from drought, overgrazing, and human population have developed in West 

Africa, especially in the Sahelian countries (Dalby 

and Church, 1973; Wade, 1974; Sterling, 1974), the 

need for repetitive inventory and surveillance of 

natural resources is becoming more critical. Landsat imagery provides a valuable tool for detecting, 

evaluating, and cataloging fixed Earth-resources 

information as well as for monitoring transient 

seasonal changes in the environment. Because of 

the large area (34,000 square kilometers) encompassed by each frame, Landsat imagery is well 

suited for obtaining a general overview of a region 

and is helpful in solving certain problems not requiring large-scale imagery. Landsat capability to 

view the Earth simultaneously and repetitively in 

four spectral bands chosen to emphasize water 

and land resources is further reason for anticipating that this satellite can yield valuable information for managing the resources of the Sahelian 

region south of the Sahara in West and Central 

Africa and of other comparable arid regions of the 

world. Because the data-recording instrument 

aboard Landsat 1 had ceased operating, images of 

Africa were not recorded for several months before 

June 1974. Nevertheless, imagery recorded during 

1972 and 1973 proved to be entirely adequate for 

the objectives of the present work. Landsat 2, 

however, was launched in January 1975. This

satellite could be employed to continue studies 

such as those undertaken in this project.

In the short time since Landsat 1 was placed in 

orbit in July 1972, considerable interest has been 

directed to using imagery from the satellite to 

study the Sahelian region lying to the south of the 

Sahara in West and Central Africa. The Office of 

Science and Technology of the Agency for International Development (AID), U.S. Department of 

State, began a program in 1973 to determine the 

utility of Landsat products in resource-management problems of the Sahel. In February 1973, 

Maurice Grolier, U.S. Geological Survey, visited 

Mali, Niger, the Ivory Coast, Senegal, and 

Mauritania to make preliminary arrangements for a 

regional remote-sensing workshop planned by AID 

for later that year. The workshop was held in 

Bamako, Mali, during April 1973 (Grolier and 

others, 1974). That same spring, AID sponsored a 

Landsat-oriented demographic study in Upper 

Volta and Niger (Reining, 1973). In addition, the National Aeronautics and Space Administration has 

supported at least two Landsat investigations of 

the Sahelian region; N. H. MacLeod, American University, has been studying plant growth and annual 

flooding in the Niger River, and the Republic of 

Mali has been conducting natural-resources Investigations using Landsat imagery. Also under 

AID sponsorship, a two-man team of Landsat 

specialists (Jones and Miller, 1974) made a visit 

during September and October 1973 to assess the 

possibilities of expanding and strengthening Landsat applications programs in the three LiptakoGourma Authority (LGA)1 countries of Mali, Upper 

Volta, and Niger (fig. 1). The present investigation 

is an outgrowth of this visit and of additional planning sessions between African and U.S. officials.

As a continuation of its program for furthering 

the utilization of Landsat products in this study

'The LGA (more fully, Authority for Integrated Development of the 

Region of Liptako-Gourma) has the objective of promoting the development of minerals, energy, water, agriculture, livestock, and fish culture in 

Mali, Niger, and Upper Volta in the region near the Niger River known as 

Liptako-Gourma (fig. 1).
APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

20°

18°

A__ MAURITANIA /

~~ • ~ ——— ——

Nioro du Sahel

Pare National de la 

Boucle de Baoule

(Tributary 

of 

^Senegal

s and boundary 

representation are not 

necessarily authoritative

100 200 300 400 500 KILOMETERS

100 200 300 400 500 MILES

EXPLANATION

Boundary of Liptako-Gourma 

Authority (LGA) region

Route of onsite ground inspection Route of aerial inspection near

Bamako by light plane

FIGURE 1.—Map of the Liptako-Gourma Authority region and adjacent areas in Mali, Niger, and Upper Volta showing principal 

physical features and localities visited during onsite inspections.

and evaluation of the natural- and humanresources problems of the Sahel, AID requested 

the U.S. Geological Survey undertake a project for 

identification of significant range- and watermanagement problems that could be studied and 

evaluated from Landsat imagery. Accordingly, M. 

E. Cooley, geohydrologist, and R. M. Turner, 

botanist, both of the Geological Survey, were 

assigned to Mali, Upper Volta, and Niger from April 

12 to May 27, 1974, to carry out the work. The problems evaluated during the writers' fieldwork included those associated with use and development of 

arable land, bush burning, location of villages and 

heavily grazed stock trails, tse-tse fly and riverblindness control, extent and duration of inundation by the annual floods of the Niger River, and 

identification of localities favorable for accumulation and production of ground water. The results 

are presented in part in a series of illustrations 

(figs. S-1—S-6) located at the end of this report

showing specifically what can be done with the 

Landsat imagery in evaluating some of these 

problems.

Acknowledgments

The cooperation of many individuals who willingly gave of their time and knowledge of the regional 

problems contributed much to the success of the 

project. Before departing from the United States, 

the writers met with Norman H. MacLeod, 

American University, who shared with them the 

results of his ongoing work with Landsat imagery 

in West Africa. Charles F. Withington, Geological 

Survey in Reston, Va., gave freely of his time and 

office space while the writers were applying 

enhancement procedures to Landsat imagery of 

Africa. Many individuals assisted the writers during their stay in Africa with technical aspects of 

the project. They are grateful for the help given in 

Bamako in the fields of botany and geohydrology
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058

by Abdoulaye Sow, agrostologist with the National 

Center of Zootechnological Research. Among 

others in Bamako with whom they conferred were 

K. J. R. MacLennan and Eric Carver, who shared 

with them their knowledge of tse-tse fly life cycles 

in relation to the vegetation and livestock of the 

area. In Ouagadougou, John Buursink and Phillip 

Roark, Comite Interafricain d'Etudes Hydraulique 

(CIEH), were helpful in arranging meetings with 

several informed individuals, in providing pertinent 

publications, and, particularly Buursink, in contributing their knowledge of the area. In addition, 

the writers conferred with D. A. T. Baldry and 

Frank Walsh, entomologists with the RiverBlindness Control Program; William Morris, 

Regional Economic Development Service Office, 

AID, Abijan; Robert Helmhols, CIEH; and Quetian 

Bognounou, botanist with the Pare Botanique, 

Centre Voltaique de la Recherche Scientifique. In 

Niamey, they conferred with lan Pattinson, 

regional officer of the Entente Fund, who gave 

them valuable information concerning agricultural 

practices in Niger.

During the writers' stay in the three capital 

cities, they were briefed and accommodated in 

numerous ways by the following members of the 

American Embassy staffs and AID officials who 

provided amenities and advice that contributed to 

a successful program: in Bamako, Ambassador 

Ralph J. McGuire, Vice-Consul David Peashock, 

Ray Denacourt, and John Garner; in Ouagadougou, 

Mark Johnson and Don Atwell; and in Niamey, 

Eugene Chiavaroli, James Hill, and Albert Baron. In 

addition, Howard B. Helman, American Embassy, 

Paris, kindly interrupted his schedule at Bamako to 

confer with the writers and to act as a translator. 

He also provided the opportunity for one of the 

writers to fly over an area being examined by tsetse control specialists. Also in Bamako, Adama 

Timbo, acting as an interpreter, quickly perceived 

many of the technical aspects of the work and was 

able to cope immediately with its complicated terminology and concepts.

To their African colleagues, the writers express 

special thanks. Many were already greatly overworked and yet they received the writers graciously. To the following, the writers are especially indebted: in Ouagadougou, to Cyr Mathieu Samake, 

Director General, LGA, and to Phillipe Kabore, 

Chief of the Documentation Center, LGA; and in 

Bamako, to Aly Dembele, Service de I'Hydraulique, 

to Sidy Zouboye, National Society for Research 

and Development of Mining, and to Bakary Toure, 

Director General Direction Nationale des Mines et 

de la Geologic.

General procedure

As originally conceived, the project was to rely 

substantially on contributions from those Africans 

knowledgeable in the land, water, and 

demographic problems of the Sahelian region. 

Africans representing the three Liptako-Gourma 

countries were to meet with the U.S. Landsat 

specialists, to examine the imagery, and, through 

basic photointerpretation techniques, to draw tentative conclusions concerning various features 

noted on the images. After this preliminary evaluation, onsite examination was to be made of as 

much terrain as feasible to check earlier interpretations and to refine the investigators' ability to 

recognize significant terrain features. The writers' 

contacts with the Africans, however, proved to be 

limited, and insufficient time was available for setting up suitable joint schedules to examine the imagery or to make onsite investigations. Consequently, the writers proceeded with the Landsat investigation without the level of direct participation 

by Africans that was originally anticipated.

Onsite investigation

Because of the short-term scope of the project, 

the areas selected for study were those easily accessible from the larger cities of the region. These 

cities are served by air passenger service and by 

good roads. Six main target sites near Bamako, 

Mopti, Tombouctou, and Gao in Mali, Niamey in 

Niger, and Ouagadougou in Upper Volta were 

selected in advance of the writers' departure for 

Africa, and imagery covering the sites was ordered 

from the EROS Data Center at Sioux Falls, S. Dak. 

The main effort was concentrated near the three 

national capitals and on part of the Inland Delta of 

the Niger River between Tombouctou and Mopti. 

Of these localities, field checking was done only 

near the national capitals, where trips of more 

than 100 kilometers into the countryside were 

made in vehicles rented locally (fig. 1). Of necessity in a region of limited accessibility, the areas inspected were along the main highways that lead 

out from the capital cities.

Additional onsite checking was made from the 

air by means of light planes and during commercial jet travel. The area west and north of Bamako, 

including the Baoule River and Pare National de la 

Boucle de Baoule, was inspected at altitudes between 150 and 200 meters above the ground from a 

light aircraft. Another flight, made in conjunction 

with an AID tse-tse control project, permitted viewing of an area south and east of Bamako. Also, 

useful information that aided in interpreting the
APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

imagery was obtained from high-altitude jet aircraft in regularly scheduled flights between the national capitals. These included the flight from 

Dakar to Bamako, two flights between Bamako 

and Ouagadougou, a flight from Ougadougou to 

Niamey, a flight upstream along the valley of the 

Niger River from Niamey to Bamako with stops at 

Gao, Tombouctou, and Mopti, and the final flight 

from Ouagadougou northward across the Sahara 

to Marseilles, France. Visibility was hindered on 

parts of these flights by the haze which prevails 

near the end of the dry season and by high clouds 

that herald the beginning of the rainy season. 

Mapping by use of the Landsat imagery was 

done only at the scale of 1:1,000,000. For further 

field use, however, scales of 1:500,000 or 

1:250,000 are recommended. (The latter scale is the 

maximum for bulk Landsat imagery.)

Selection of imagery

Selection of imagery was made from computer 

printouts obtained from the EROS Data Center. 

Sufficient time was not available before departure 

from the United States for the writers to visit the 

Data Center and to make selections directly from 

its files, although this would have been the preferred procedure. Approximately 30 different 

scenes were finally selected providing coverage by 

several frames around each of the six cities in the 

LGA region. In some instances, the same areas 

were covered on two successive dates. Such sequential views provided opportunity to evaluate applications of Landsat imagery to seasonal changes 

on the land surface. Most of the Landsat images 

used were 9- by 9-inch positive transparencies 

(scale 1:1,000,000). All four spectral bands were 

utilized, and, in some instances, scene features 

were enhanced by using diazochrome overlays 

where band 4 (0.5-0.6 micron) was reproduced in 

yellow, band 5 (0.6-0.7 /*) in magenta, and band 7 

(0.8-1.1 n) in cyan. This technique was particularly 

useful for examining details of the vegetation and 

for mapping surficial geologic features. Two other 

types of Landsat data were also employed; they 

were 9- by 9-inch false-color infrared red composites and 18- by 18-inch black-and-white prints of 

band 5 only (scale 1:500,000).

Geohydrologic Setting

Mali, Niger, and Upper Volta occupy part of a 

large relatively stable structural platform that extends across most of northern Africa. The platform 

is formed principally by Precambrian basement 

rocks which are discontinuosly mantled by thin 

sedimentary rocks of Paleozoic to Cenozoic age.

Imposed upon this broad platform are several gently downwarped sedimentary basins which are bordered by low uplands and plateaus (Archambault, 

1960). The basins are major features, about 600 km 

or more across. Mali lies in parts of two of these 

basins, the Bassin du Soudan and the Bassin du 

Niger (fig. 1). Niger lies mainly in the Bassin du 

Niger, and Upper Volta lies in low uplands along 

the southern flanks of both basins. The Precambrian basement rocks, including a variety of granitic and foliated metamorphic rocks, are exposed 

mainly in the uplands and plateaus (Marvier, 1952). 

The Paleozoic and Mesozoic sedimentary rocks 

crop out along the flanks of the structural basins 

or lie at relatively shallow depth beneath Cenozoic 

sedimentary rocks which occupy the central parts 

of the basins (Archambault, 1960). Mesozoic strata, 

however, are not recognized southwest of a line 

trending roughly northwestward through Niamey 

and Tombouctou. Surficial deposits, principally of 

Quaternary age, are thin but widespreadoccurring mainly as stabilized and active dunesand deposits, as stream alluvium, including deposits of the Inland Delta of the Niger River, as 

scattered terrace deposits, and as widespread 

laterite duricrusts. The laterite forms surficial ferruginous crusts 1 to 10 m thick over more than 80 

percent of Upper Volta, southern Mali, and southern Niger and lends a harsh reddish-brown aspect 

to the landscape. All the consolidated rocks and 

unconsolidated deposits yield water to some extent, but the principal ground-water reservoirs are 

in the coarse facies of the Mesozoic and Tertiary 

sedimentary rocks occupying the central parts of 

the downwarped basins and in the unconsolidated 

alluvium, especially the deposits along the Niger 

River. Additional descriptions of thickness and lithology and the associations of the rocks with vegetation, with ground-water supplies, and with farm 

and range parameters are summarized in table 1.

The LGA countries lie principally in the low 

(200-650 m above mean sea level) semiarid Sudan 

and Sahel Savanna and the arid Saharan regions 

of West Africa where rainfall occurs only during 

the high-sun months of May to October. The 

southern parts of these countries receive more 

than 1,000 millimeters of rainfall annually (fig. 2). 

Rainfall during the high-sun period has to sustain 

plant and animal needs throughout the long dry 

season that lasts roughly from October to May. 

Bamako and Ouagadougou commonly have a dry 

season of 5 to 7 months and receive less than 25 

mm of rain during this time. At Niamey, Gao, and 

Mopti, the dry season lasts from 7 to 9 months; at 

Tombouctou, the dry season is longer than 9 

months (Church, 1968). Thus, any prolongation of 

the dry season or shortening of the rainy season
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058

Boundary of Liptako-Gourma 

Authority (LGA) region

_ _ .__ MALJRITANIA/ 

Nioro du Sahel MALI x-—A1000 -. 

tributary ^

I nf «

S^ '

IVORY COAST

100 200 300 400 500 KILOMETERS

100 200 300 400 500 MILES

FIGURE 2.—Mean annual precipitation, in millimeters, in parts of Mali, Niger, and Upper Volta (taken from Archambault, 1960, fig. 2).

has disastrous effects on the farming and grazing 

economy of the region. The precipitation 

decreases northward, and, in northern Niger and in 

Mali north of Gao, precipitation is less than 200 

mm annually. There, rains fall mainly during July 

and August. Because of prevailing high mean annual temperatures (27°-29°C), evapotranspiration 

is also high. Therefore, during the dry season, 

most streams and small reservoirs dry up, soil 

moisture and shallow ground-water supplies are 

depleted, and the range vegetation becomes dormant.

The Niger, the Red, White, and Black Voltas, and 

the Senegal Rivers draining the Sahelian region of 

West Africa receive most of their runoff from precipitation that falls on a rather low but broad highland that extends east-west across northern 

Guinea, southern Upper Volta, northern Dahomey, 

and southern Mali. Annual rainfall in this highland 

commonly ranges from 1,000 to more than 1,250 

mm (fig. 2). The Niger and Volta Rivers all empty 

into the Gulf of Guinea. The Volta Rivers enter the 

Gulf through Lake Volta in Ghana, but the Niger 

takes a long circuitous route northward to the 

edge of the Sahara near Tombouctou, where it 

bends eastward and then southeastward past Gao 

and Niamey (fig. 1) on its course to the Gulf of 

Guinea. The Senegal River flows generally northwestward to the Atlantic Ocean north of Dakar. 

These three great rivers and their main tributaries 

are in flood stage during the rainy season; this 

flooding is commonly referred to as the annual 

flood. In central Mali, the annual flood of the Niger 

River spreads spectacularly over much of a vast Inland Delta where flood-retreat farming is practiced 

extensively (fig. 1).

Savanna Vegetation

The semiarid savanna vegetation of West Africa, 

from its southern limit at the Tropical Forest Zone, 

grades progressively through open woodland to 

shrubland to its northern limit at the Sahara. The 

major vegetation communities are oriented as a 

series of east-west parallel bands in response to 

the dominant rainfall gradient across Africa. The 

gradient of decreasing precipitation toward the 

north is accompanied by a progressive change in 

the character of the vegetation. To the south, 

where rainfall is highest, the vegetation comprises 

tall trees with large evergreen leaves; there is virtually no grass understory. This is the true forest. 

Proceeding northward through 10 or 15 degrees of 

latitude, these large-leaved forms are gradually 

replaced by short trees and shrubs which have 

small often finely divided drought-deciduous
APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

TABLE 1.— Brief description of the stratigraphic units and their utilization by man in the areas near Bamako, Mali, Niamey, Niger, and 

Ouagadougou, Upper Volta

tp

UJ

o 

o

o

c

<D 

CJ

'oo

O </) <D

Paleozoic

Period

Quaternary

Quaternary 

and 

Tertiary)?)

Tertiary

Cretac

Epoch

Holocene

Pleistocene(?)

Pleistocene

Pleistocene 

and 

Pliocene!?)

Miocene

Eocene 

ecus

Ordov cian

Precambrian

Stratigraphic 

unit

Dune deposits near 

Niamey (dunes were 

not inspected in 

other areas)

deposits Alluvial 

Channel alluvium 

of Niger River 

(excluding 

deposits of the 

Inland Delta)

Flood-plain 

alluvium along 

Niger River 

(excluding 

deposits of the 

Inland Delta)

Gray alluvium

Yellowish-buff 

alluvium and 

equivalents

Brown alluvium 

in vicinity 

of Ouagadougou

Laterite

Continental Terminal 

(Archambault,1960)

Cretaceous-Eocene 

sedimentary rocks 

undifferentiated

Ores Ordovicien 

(Archambault,1960)

Basement complex

Distribution and thickness

Small discontinuous areas on terraces and slopes near the Niger River 

and on broad gentle slopes underlain principally by laterite away 

from the river; generally less than 10 m thick.

In wide and braided channels of the Niger River and in adjacent low 

terraces inundated by the annual flood.

Forms terraces generally not inundated by the annual flood; terrace is 

3 to 6 m high (above low flow stage of the river) and from a few 

meters to more than 2 km wide; unit generally thin, in places less 

than 6 m thick, particularly near Bamako where older consolidated 

rocks are exposed in the river.

Underlies central areas and much of gentle slopes of broad flats and 

narrow flood plains along streams in small valleys in uplands away 

from the Niger River; unit is thin and is less than 1 m thick in much 

of the broad flats; locally unit is more than 3 m thick along streams.

Exposed on gentle slopes forming broad flats; at many localities, it 

comprises bulk of alluvium of the broad flats; unit forms conspicuous terrace 5 to 1 5 m high along the Niger, Senegal, and White Volta 

Rivers and a lower terrace along some of their tributaries; thickness 

varies locally, but in places the unit probably is greater than 20 m 

thick.

Exposed mainly in the perimeter area of broad flats; thickness is 

unknown.

Exposed over about 80 percent of the area on ridges and mesas, on 

steep slopes, on colluvium or consolidated rocks, over broad plains, 

and on river terraces; also present beneath alluvial deposits; 1 .5 to 

10 m thick.

Present only near Niamey (in Bassin du Niger) where it underlies 

laterite capped buttes, ridges, and broad slopes; 100 to 200 m 

thick.

Not exposed, present only in subsurface of Bassin du Niger near 

Niamey; more than 400 m thick.

Forms uplands in Bamako area; not present or not recognized in the 

other areas; unit generally capped by laterite; 50 to 200 m thick.

Few small isolated outcrops in area.

______ -.-.--..-....-_-. . ...
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058

TABLE 1.— Brief description of the stratigraphic units and their utilization by man in the areas near Bamako, Mali, Niamey, Niger, and 

Ouagadougou, Upper Volta Continued

General lithologic description

Consists of active and stabilized sand dunes; 

includes many composite dunes and a few 

climbing and falling dunes; older dunes 

show a slight amount of consolidation and 

development of soil.

Consists chiefly of unconsolidated sandy and 

silty alluvium, many large sand bars show 

huge current marks.

Consists of unconsolidated sand and silt containing a minor amount of gravel

Consists of unconsolidated to very slightly 

consolidated light-gray to grayish-buff clay 

and silt; contains some sand, little 

gravel — mainly of grit and small pebbles; 

contains considerable organic material 

especially along streams.

Consists of slightly consolidated yellowishgray, light-brown, or buff clay to silt containing considerable sand and little 

pebble-sized gravel; unit generally is yellowish in the Bamako and Ouagadougou 

areas and brownish near Niamey; as much 

as uppermost 2 m of unit may show weak 

development of latente.

Consists of weakly to moderately consolidated brownish-gray silt to mainly pebblesized gravel composed of laterite detritus, 

gravel concentrated mainly near the laterite outcrops; silty and sandy parts are in the 

downslope areas; at many places, unit is 

overlain by moderately hard laterite forming a layer more than 1.5 m thick.

Consists of several units, each unit has different thicknesses, composition, amount 

of cementation, bedding features, and included alluvial detritus; generally hard to 

very hard; more ferruginous near Niamey 

and Gao than in other areas; older units 

may be siliceous and contain fractures 

formed along joints.

In a few exposures that were inspected, unit 

consists of silty to sandy deposits modified 

or partly altered during formation of the 

overlying laterite.

Includes, in descending order, the Eocene, 

Middle and Upper Cretaceous, and Continental Intercalate (Archambault, 1960); 

consists of clay to gravel deposits; upper 

part mainly clay and sand, lower part 

mainly sand and gravel.

Consists mainly of firmly cemented 

sandstone that can be divided into several 

distinct units; units are fractured extensively along joints and small faults.

Consists of granitic and metamorphic rocks; 

some of metamorphic rocks are standing 

on end; rocks are deeply weathered to 

more than 15mm the few exposures inspected.

Utilization by man

Ground-water supplies

Generally too thin and of too small an areal 

extent to be a source of ground water; 

highly permeable sand allows much infiltration and little runoff from precipitation.

Deposits are permeable and yield water to 

shallow temporary dug wells during low 

flow periods, but annual flooding prohibits 

development of the unit by permanent 

wells.

Yields dependable supplies of ground water 

to wells because of its proximity to the 

river; well yields probably are not large because of the general thinness of the unit, 

larger quantities of water, perhaps sufficient for some irrigation, can be obtained 

by construction of collector wells in the 

unit.

One of the alluvial deposits supplying small 

amounts of water to dug wells of villages 

and fields along small streams; unit probably lies above the water table in most of the 

broad flats

Probably supplies a small amount of ground 

water to many shallow dug wells constructed in the broad flat areas.

Yields small amounts of water to dug wells.

Part of laterite underlying alluvial deposits 

apparently yields small amounts of water 

to dug wells; fractures aid infiltration from 

precipitation through the laterite and into 

the underlying rocks.

L 

Figure 9 showsof typical conditions twoccurrence some 

of thedug wells have dry that becomeduring the fewpast years.

Where saturated, unit should yield dependable small to moderate supplies of water to 

drilled wells.

Where saturated, unit should yield dependable small to moderate supplies of water to 

drilled wells.

Where saturated, probably would yield small 

amounts of water to drilled wells; where 

unit is highly fractured, well yields would 

be greatly increased.

Weathered part of unit is known to yield small 

amounts of water to dug wells near 

Ouagadougou; where rocks are highly 

fractured, they probably would yield some 

ground water to drilled wells.

Farm and range

Extensive local use for crops; mam unit 

farmed between Niamey and Dallol 

Bosso; when soil and vegetation cover of 

stabilized dunes are disturbed by cropping, 

overgrazing, or by natural causes, the 

dunes are liable to severe wind erosion and 

blowout activity.

Partially utilized in flood-retreat farming and 

for grazing; unit can be farmed much more 

intensively.

Partially used for farming and for orchards; 

grass and brush foliage supports considerable stock; unit comprises best arable land 

in the Bamako and Niamey areas and can 

be more intensively developed for farming, 

with water diverted from the Niger River.

Unit is widely cultivated everywhere, but it 

comprises the only arable land in the uplands near Bamako and Ouagadougou; in 

many places, the unit is 30 cm thick, 

thereby limiting its usefulness for farming, 

especially to deep plowing even if farm 

machinery would become available; many 

villages are situated on the unit because 

they are clustered in areas where there are 

shallow water supplies and arable land.

Development of laterite in the topmost beds 

of the unit precludes its use for farming of 

crops, although the unit supports range 

grass and browse vegetation; unit probably can support orchards and shade trees; 

unit is severely sheet eroded especially 

near villages where land has been subjected to extreme overuse by man's activities.

Used as rangeland even though many exposures are nearly denuded of vegetation and 

are subjected to severe sheet erosion; laterite detritus in unit and associated laterite 

is excellent for road metal.

Because of extensive distribution, unit forms 

principal rangeland of the area; excellent 

as building stone and makes attractive 

walls; when crushed, used as road metal.

Generally exposed only in steep slopes that 

are undergoing severe erosion; forms a 

minor part of the rangeland.

—— — — —

Mainly used for grazing; insufficient amount 

of soil developed on unit restricts farming.

Small exposures form minor part of rangeland.
8 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

leaves. The changes in leaf morphology and plant 

stature are accompanied by an increased openness of the woody components, the openings between the woody plants occupied by grasses. The 

number of thorny species also increases. Terms 

widely used in West and Central Africa for the 

dominant transcontinental vegetation zones from 

south to north are Guinea Savanna, the Sudan 

Savanna, and the Sahel Savanna (fig. 3).

A vegetation gradient comparable to the southto-north cline of vegetation types can be seen 

locally within the Guinea and Sudan Zones in 

changes that proceed from moist river terraces to 

the relatively dry uplands. River terraces within 

these regions contain more moisture for the plants 

than local precipitation alone provides, and the 

rivers are bordered in many places by narrow 

strips of tall large-leaved trees whose main areas 

of distribution lie hundreds of kilometers to the 

south. The term "fringing forest" has been applied 

to these narrow strips of dense vegetation. This 

type of forest is comparable to the "gallery forest" 

of North America.

The present savanna vegetation in West Africa 

has been exposed to more or less continuous 

heavy use by man for centuries and perhaps 

millenia (Hopkins, 1965) and consequently has 

been altered greatly (fig. 4). Since the late 1960's

and early 1970's, all zones of the savanna have 

been under severe stress from intensified drought 

conditions, coupled with increased population 

pressures of man and proliferating domestic herds 

built up during the 1950's and early 1960's, largely 

with inadequate regard to proper management 

practices. (A wet cycle prevailed in the region from 

about 1955 to 1966.) Where lands are cultivated, a 

combination of cutting, burning, and fallowing is 

also practiced. This swidden (slash-and-burn) form 

of agriculture has changed the area of earlier existing dense forest vegetation to its present form 

of open forest or shrubland. These practices have 

increased the availability of farmland and 

rangeland for man's use but have greatly modified 

or obliterated the original vegetation of the Sudan 

and Guinea Zones. Contrary to much of popular 

opinion, the Sahel vegetation (north of the 450-to 

640-mm isohyets) has been less affected by man's 

activities than that of the two southern zones 

where rainfall is greater (Church, 1968). In the 

Sahel, there is less grass to carry fires, population 

levels are low, and possibilities for cultivation 

without irrigation are slight, especially in areas adjacent to the Sahara; consequently, the natural 

vegetation has been modified only by grazing. Accordingly, the savanna areas of most critical concern for maintaining a proper balance between the

6°

Boundary of Liptako-Gourma 

Authority (LGA) region^

'Torhbouctou«

16°L—— /r»__JV..J^AURITANIA__S A/H E L 

*Nioro du Sahel MALI

.x ^47 ^ \-ii' 

1/S U D A N \L

Names and boundary 

representation are not 

necessarily authoritative

0 100 200 300 400 500 KILOMETERS

0 100 200 300 400 500 MILES

FIGURE 3.—Vegetation zones in parts of Mali, Niger, and Upper Volta (taken from Keay, 1959).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 9

FIGURE 4.—Photographs taken aloftg the White Volta River showing influence of man's activities on vegetation and terrain.

A. Vegetation and terrain show little effect of man's activities during the year ending May 1974. Grass has been moderately grazed, 

and some branches have been cut from the tree in center middle ground.

B. Grass understory vegetation has been somewhat altered by burning. The general absence of soil-holding vegetation allows for 

minor sheet erosion.
10 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

FIGURE 4.—Photographs taken along the White Volta River showing influence of man's activities 

on vegetation and terrain—Continued.

C. Burning has removed the grass and woody understory vegetation. A few trees have been cut for firewood; trunks and branches 

larger than about 10 centimeters in diameter are not utilized. The bark on some of the living trees is charred but is thick enough so 

that the trees are not injured by fires. This area, stripped of its ground cover, is susceptible to accelerated sheet erosion.

D. Wood cutting and burning have removed all the vegetation on a low terrace formed from easily erodable yellowish-buff alluvium. 

A small village lies just to the left of the picture. The White Volta River lies just off the photograph to the right. Denudation permits development of accelerated sheet erosion which soon will be accompanied by severe gullying.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 11

natural vegetation and man's use of the land are to 

the south, where woodland is constantly being replaced by grassland, rather than to the north, 

where the original vegetation has been less 

detrimentally affected by man.

The Sudan Savanna, which lies in a belt 200 to 

400 km wide north of the Guinea Savanna, includes trees 8 to 16 m high, many of which belong 

to the same species found in the zone to the 

south. Especially common are the doum palm 

(Hyphaene thebaica), danya (Sclerocarya birrea), 

and soapberry tree (Balanites aegyptiaca), all of 

which increase in dominance northward toward 

areas of increasing aridity and are represented little or not at all in the Guinea Savanna. Grasses 

grow 1 to 1.75 m high. Because the grass species 

in the Sudan Savanna are less course than those 

to the south, they are more valued as forage and 

less often deliberately burned (Church, 1968).

In the region of Bamako, which lies on the border between the Guinea and Sudan Zones, and 

Ouagadougou, which is in the central part of the 

Sudan Savanna (fig. 3), the following geobotanical 

categories are recognized: (1) alluvial flats and 

valleys (generally containing ground water with a 

shallow water table), (2) uplands, (3) slopes of 

buttes and ridges underlain by laterite and (or) 

sandstone, and (4) the riverine fringing forest. In 

each of these categories, the vegetation has been 

greatly altered by man's activities. For example, 

villages in the vicinity of Bamako occur at regular 

intervals of about 5 to 15 km. The land is heavily 

cultivated around the villages, and areas between 

villages usually are cultivated as well. All the uncultivated vegetation is in some stage of recovery 

from burning or clearing. Presence of grasses is 

variable in the Bamako area, as elsewhere in the 

savanna zones, largely because of local differences in environment that affect moisture 

availability for plant growth, differences in the intensity of grazing, and in the frequency and timing 

of bush fires.

On the alluvial flats, provided that destruction of 

the vegetation is not extreme, the first category of 

vegetation comprises such trees as the shea butter tree (Butyrospermum parkii), locust bean tree 

(Parkia biglobosa), dry-zone mahogany (Khaya 

senegalensis), African rosewood tree (Pterocarpus 

erinaceus), and species of Combretum. Some of 

these trees, such as the shea butter, are of 

economic importance and are preserved even in 

areas of heavy disturbance. Another economically 

important tree that is closely associated with 

villages and can be seen standing sentinellike in 

fields is the baobab (Adansonia digitate). Many of

the same species that grow on the flats grow on 

the laterite-capped ridges and buttes (vegetation 

category 2), where edaphic conditions are drier 

than on the alluvial flats, but the plants are reduced in size. In addition, the kapok tree (Bombax 

costatum), harike (Anogeissus leiocarpus), and figs 

(Ficus species) are present. Along the slopes of 

scarps, particularly of the buttes and hillslopes, 

where edaphic conditions are intermediate between the ridge and butte surfaces and the alluvial 

flats, the vegetation (category 3) is usually denser 

than that above or below and probably attains 

75-to 100-percent foliar coverage during the rainy 

season. Here may be the most northerly habitats 

for the tse-tse fly. These hill-slope forests, where 

especially dense, stand out sharply on properly 

enhanced Landsat imagery (fig. S-1A). The fourth 

category of vegetation in the Bamako and Ouagadougou regions is the riverine fringing forest. A 

partial listing of the trees in this forest includes a 

palm (Raphia Sudanica), a fig (Ficus capensis), a 

cola (Co/a cordifolia), and malmo (Syzygium 

guineense).

The driest area the writers were able to examine 

in detail was in the region of Niamey, Niger, which 

is near the northern limit of the Sudan Savanna 

(fig. 5). One of the striking differences between the 

vegetation in this region and that toward the 

southern limit of the Sudan Savanna near Bamako 

is the increase in small-leaved species such as the 

Acacias and in the spiney plants. One of the most 

common spiney trees is African myrrh (Commiphora africana). Shrub communities grow on dry 

sites, dominated by a species of Combretum. The 

shrub canopy grows to about 2 m in height and is 

interrupted irregularly by a low tree, the soapberry. 

In general, the grasses are shorter and much less 

abundant in the vicinity of Niamey than in the 

region of Bamako and Ouagadougou. Fringing 

forests of evergreen broad-leaved trees are absent 

from this region (and northward), the watercourses 

being lined by certain drought-deciduous Acacias. 

As a consequence, intermittent stream courses do 

not stand out sharply on Landsat imagery taken 

during the dry season.

Landsat Imagery in Relation to Range and

Water Assessments

In the following sections the writers describe 

the main applications they discerned for use of 

Landsat imagery in resolving land-resources problems affecting the people of the LGA countries. 

In addition, tentative answers to some pertinent 

questions relative to the use of Landsat imagery in 

range and water management are given in table 2.
12 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

FIGURE 5.—Photograph showing west side of the Niger River valley near Niamey, Niger. In the foreground, a species of Combretum 

(dominant) and Pterocarpus (left) on detritus formed from a terrace capped by laterite. This photograph, taken on May 18, 1974, 

near the end of the dry season, shows many leafless plants, a typical condition for this time of year. Doum palm, soapberry tree, 

shea butter tree, among other trees, grow on the light-colored sandy terrace deposits and dunes in the background. This area is in 

the northern (dry) part of the Sudan Savanna zone. Two buttes along the horizon consists of fine-grained "Continental Terminal" 

semiconsolidated sand and clay capped by resistant laterite duricrust.

Three main factors are important in the use of 

the imagery and to its interpretation:

1. Adequate onsite investigation is essential for 

accurate identification, mapping, or monitoring of geohydrologic, vegetative, and agricultural phenomena.

2. Many conclusions concerning hydrologic features, disease, and insect control must be 

deduced indirectly from the imagery by observing geologic and vegetational features. 

For example, shallow ground-water zones and 

tse-tse fly habitats are not identified by making direct observations of water and flies; the 

presence of these is inferred by correlation of 

conditions observed in the imagery with geological and vegetational features known to be 

associated with water and flies. Similarly, the 

extent of arable soils can be determined principally by relating the occurrence of such 

soils with geologic features that are readily 

discernible on the images.

3. The effects of man's use of the land must also 

be considered when interpreting Landsat imagery. In areas visited by the writers, the land 

around most villages is denuded of grass and 

forbs as a result of trampling by men and 

livestock, overgrazing, brush burning, and 

cultivation (fig. 6). These activities produce accelerated sheet erosion and wind deflation, 

both of which exert a profound effect on the
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 13

distribution and thickness of arable soils. 

Lastly, so much of the rangeland has been 

burned each year or heavily grazed or cleared 

during the past centuries that no vegetation is 

left that can be considered as unmodified.

River-blindness control

River blindness (Onchocerciasis) is a disease of 

man caused by a filarial worm (Onchocera volvulus). The causative organism is transmitted by a 

black fly (Simulium damnosum). Outbreaks of this 

disease, which ultimately causes blindness, are 

common along rivers because the riparian habitat 

is essential for fly reproduction. Simulium eggs are 

laid in streams or ponds where they hatch. The larvae feed by straining microorganisms out of the 

water; however, slowly moving water carries too little food to the sedentary larvae, and they starve. 

Therefore, larvae survive most successfully at sites 

of fast-flowing water such as rapids or dam 

spillways (fig. 7).

Recently, a multinational effort was initiated to 

control river blindness (Tomiche, 1974). The approach taken is to kill the larvae at all the breeding 

sites in an area of 700,000 square kilometers in the 

Volta River basin. The larvae are killed by dropping

from the air a specially formulated pesticide into 

streams at all known breeding sites. Accurate 

maps are necessary when preparing detailed flight 

plans for reaching known fly-breeding sites, and 

the absence of appropriate maps is hampering the 

programs along the Black Volta River (Frank 

Walsh, oral commun., 1974). Although Landsat imagery, because of its lack of sufficient resolution, 

does not appear useful in locating specific sites of 

fast water or rapids, it does have potential application for correctly locating a river system in regions 

for which maps are poor or incomplete and for 

identifying small reservoirs that may be breeding 

sites.

The location of dams has become a critical step 

in the control program because dam spillways 

often harbor large populations of the fly larva 

(Tomiche, 1974). The stockwater dams are difficult 

to keep track of because they may last only a few 

years and because new dams are constantly being 

built (fig. S-2B). Landsat band 7 imagery or colorcomposite imagery can be especially suited to locating these bodies of water if the reservoirs are 

larger than about 200 m in diameter (30 hectares in 

area). For elongate reservoirs, the total area may 

even be smaller.

FIGURE 6.—Photographs showing effects of man's activities around small villages.

A. Newly hand-cultivated field adjacent to a recently dug well 

(indicated by circular concrete ring) near Ouagadougou, Upper 

Volta, May 14, 1974. The well obtains ground water from 

weathered granite, which in this area underlies a surficial mantle of alluvium and laterite.

B. Accelerated erosion along pathway leading through newly 

planted fields near Ouagadougou, Upper Volta. Erosion was 

caused by early rains of the 1974 wet season.
14 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

TABLE 2— Tentative assessment for relating Landsat imagery to selected problems in range and water management in the 

Liptako-Gourma countries

(1) Can shallow water tables and zones of ground-water discharge 

be identified and their areal extent mapped?

Shallow water tables are difficult to separate from zones of 

ground-water discharge on Landsat images because both occur at 

or near the land surface and both are associated with dense 

growths of vegetation. Discharge of ground water, however, 

maintains flow of streams and ponds in stream channels well after 

the end of the rainy season. Dense growths of vegetation are 

shown on the imagery along some streams, principally in alluvial 

valleys, near Bamako and Ouagadougou (figs. S-1, S-2; frames 

1117-10232 and 1095-10000 taken in October and November 

1972, respectively). The heavy growth suggests the presence of a 

shallow water table and probably ground-water discharge into the 

stream channels at the time the imagery was taken. For best 

results in differentiating between the two conditions, imagery 

taken periodically throughout the dry season should be examined 

for changes in vegetated areas affected by shallow ground-water 

discharge zones.

(2) Can weathered or fracture zones in the Precambrian crystalline 

basement rocks, likely to be productive of ground water.be 

identified?

Generally, the Precambrian basement rocks are concealed by 

laterite duricrust or by a thin surficial mantle of alluvium. Near 

Ouagadougou, hand-dug wells, penetrating through the 

laterite, yield small amounts of water (enough for stock, 

villages, and bucket irrigation of small cultivated plots) from 

deeply weathered regolith developed in the upper part of 

basement rocks. This area of low relief is identifiable on the 

imagery because of the generally light, rather even color tone 

and general lack of conspicuous drainage features (fig. S-2).

Linears identifiable in the imagery in areas of consolidated rocks 

may be related to faults, fractures, and joints along which water 

movement and accumulation are facilitated. Weathering in such 

zones, and especially at points of intersection, would improve the 

potential for accumulation of important sources of water.

(3) Can good sites for surface-water catchments be identified?

Sites favorable for small surface-water catchments are widely 

distributed because of the general low permeability of the older 

consolidated rocks as well as the younger surficial deposits. 

Ephemeral lakes and ponds, which are discernible with repetitive 

imagery coverage, give clues as to locations for potential 

catchment sites that can be improved by artificial excavation and 

(or) low earth dams. Constrictions or narrows in stream channels 

in areas of outcropping consolidated rocks can also be identified to 

give clues for the location of small dams for surface-water 

catchments. Larger areas that generally are unfavorable for 

surface-water catchment sites are mainly those mantled by 

thick, relatively permeable, dune-sand deposits or those in 

areas of intensively fractured rock where the water table is at 

considerable depth. The main dune-sand and principal 

fractured areas are identified readily on the images (figs. S-4, 

S-65). The smaller areas, where surface-water catchments 

may not be successful, are on sandy terraces and slopes of the 

Niger River valley, on the sandy alluvium of at least part of the 

dallols, and on sandy alluvium along small streams that drain 

principally dune-mantled areas. The Landsat imagery aids in 

recognizing these areas, which generally appear light-colored 

in comparison to adjacent laterite duricrust, consolidated 

rocks, or the Continental Terminal where capped by laterite 

duricrust.

(4) Can land potentially useful for irrigated crop production be 

identified?

The Niger River valley is, of course, the most obvious choice. 

Much of the arable land is identifiable on the Landsat imagery 

and, with onsite inspection, can be mapped in considerable 

detail using Landsat imagery at a scale of 1:250,000. (See 

section on "Factors affecting availability of arable land.") Only 

the flood plain of the Niger River and the Inland Delta, however, 

are capable of supporting large-scale farming operations. In 

these areas, large amounts of water are available for irrigation 

by diversion from the Niger River and, in the Inland Delta, from 

the Niger and the Bani Rivers. Supplemental ground water can 

also be obtained for irrigation in these areas from properly 

constructed wells.

Small vegetable plots can be farmed along the various segments of 

the braided channel of the Niger River, as for example near 

Niamey (fig. 12). The braided channel is easily mapped by the 

imagery (figs. S-4, S-5). Analysis of Landsat imagery is useful for 

inspection, leading to final selection of the channel reaches most 

suitable for farming throughout the Niger River valley.

Flood-retreat cultivation is the principal farming technique 

practiced by the people living along the Niger River in Mali. It 

is practiced to a lesser extent in Niger, where this method of 

cultivation is not well developed (Church, 1973). The lands near 

the river are seasonally flooded, and, as the floodwaters 

recede, the farmers use the wetted lands to cultivate a definite 

sequence of crops: maize, grain sorghum, sweet potatoes, 

cucurbits, tomatoes, and beans in order from top to bottom on 

the slopes. Grain sorghum is sown on the gently sloping outer 

valley floors and rice is sown on the flattest areas of maximum 

depth of inundation. Landsat imagery and the capability 

Landsat provides for repetitive observation make it well suited 

for determining the maximum limit of flooding, thereby 

providing a means of predicting crop size in advance of 

harvest. By knowing a crop yield potential in advance, 

impending needs and requests for assistance can be tailored 

accordingly.

(5) Can distinctions in the relative seasonal productivity of grass 

and browse vegetation be made from the imagery?

The Landsat imagery is ideally suited for detection of seasonal 

trends in rangeland plant growth. Qualitative differences can be 

observed on sequential imagery provided observations are made 

on enhanced images; for example,color composite photographs 

or diazochrome overlays. To obtain quantitative data showing 

seasonal trends, sophisticated ratioing techniques can be used to 

eliminate the undesirable effects of variables such as haze and sun 

angle. These techniques require the use of computer-compatible 

tapes or, if images are used, a video system with a capacity for 

ratioing and electronic slicing.

The ability to detect the density of crops in fields as a measure of crop 

success and crop yield would be extremely useful (W. Morris, oral 

commun., 1974), although the main crops, such as millet and 

sorghum produce a sparse cover that might be difficult to detect. 

The time for analysis and degree of sophistication required to 

assess the applicability of the data for crop-yield estimate was 

beyond the scope of this project. Work by others, however, 

indicates that the data can be used to aid in identifying crop types 

and estimating yields for fields with areas of 32.4 hectares or 

greater (Wigton and VonSteen, 1973; Morain and Williams, 1973).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 15

TABLE 2—Tentative assessment for relating Landsat imagery to selected problems in range and water management in the 

Liptako-Gourma countries—Continued

(6) Can areas of relative overgrazing and undergrazing be identified 

from the imagery?

Overconcentration of livestock around existing water points has led 

to complete denudation of vegetation in many localities. Landsat 

images clearly show some trails leading to water points as 

elongate light-colored streaks (fig. S-3). These were not examined 

in the field, but it is apparent that the trails appear light colored on 

the images because of denudation through overgrazing. In 

support of this, villages are often clearly discernible as light areas 

(fig. S-3). The high reflectance at the village sites does result from 

denudation by overgrazing, wind deflation, and sheet erosion, as 

well as perhaps other causes.

(7) What is the relationship between the laterite duricrust of 

interfluvial upland surfaces versus grass and browse density? In 

the absence of perennial water, soils derived from what types of 

geologic terrains are most conducive to productive grazing and 

browse lands?

Alluvial soils (mainly those derived from the gray alluvium) are 

the most productive grazing and browse lands. (See section on 

"Factors affecting availability of arable land.") Grass and shrub 

foliage is far denser there than on the adjoining laterite terrain. 

At many places, the laterite duricrusts form bare wind-swept 

surfaces nearly devoid of soil and vegetation. The Landsat 

imagery has been demonstrated to be highly useful in the 

distinction between alluvium and laterite in the Ouagadougou 

area (fig. S-2B) and near Niamey and Tombouctou (figs. S-5, 

S-6). More subtle distinctions between the three types of 

alluvia (brown, yellowish-buff, and gray) will require special 

Landsat false-color composites.

(8). What do Landsat data tell us about desert encroachment as 

indicated by migrating sand dunes and wind and sheet 

erosion, accelerated in either the current drought cycle or by 

antecedent drought conditions?

Migrating or active sand dunes do not extend as far south from the 

Saharan region as do stabilized dunes (fig. S-6B). Stabilized 

west-southwest—east-northeast longitudinal dunes near 

Tombouctou are covered by weakly developed slightly 

reddish-brown soils. These dunes are not now impeding the flow 

of the Niger River, although they have doubtless influenced the 

river's course and flow regime in the past. At present, the river 

flows through these dunes in one wide main channel as well as in 

a system of tributary channels, many of which carry water only 

during the flood seasons.

Both the active and stabilized dunes are easily mapped by the 

Landsat imagery. Denudation of vegetation and concommitant 

blowout activity can also be recognized on the images. To 

define and to separate the natural from the man-induced 

effects—and to determine whether these phenomena are a 

result of the current drought or the aggregate effects of man's 

abuse of the land during previous decades or even 

centuries—would, of course, require much onsite investigation.

Accelerated sheet erosion, including severe gully erosion, is 

commonly observed in all the areas the writers were able to visit or 

to discern on the images. (See section on "Accelerated Erosion.") 

The present advanced stage of gully dissection and the large area 

involved in accelerated erosion strongly suggest that these 

processes have been in progress for several decades. In the 

localities visited by the writers, man's activities in recent 

decades appear to have aggravated these processes more than 

have adverse effects of the present drought cycle.

Continuous monitoring by Landsat can provide 

additional information that may be useful in the 

River-Blindness Control Program. Seasonal 

changes noted in the flow regime of rivers might 

indicated conditions favorable for growth of the 

black fly larvae. According to Malian officials, considerable relocation of the village peoples takes 

place in West Africa, principally because of (1) 

disease (including river blindness), (2) water problems (from drought and pollution), (3) changing 

cultivation practices, and (4) superstitions. Large 

villages are readily discernible on the images, and 

areas having or lacking small villages are visible 

(fig. S-3). Thus, repetitive Landsat observations 

could be made to locate new villages and abandoned old ones.

Tse-tse fly control

The life cycle of the tse-tse fly, which is the 

main carrier of bovine encephalitis (Nagana), has a 

relationship to the density of vegetation. This relationship is being exploited in a program to 

eliminate this disease from large tracts of land in 

Mali. The tse-tse fly is inactive at midday, during 

which time it seeks shade within nearby forests. 

The fly can be controlled by spraying small clumps

of these forests with insecticides or, where large 

areas of sheltering forest occur, by spraying the 

forest peripheries. The tse-tse fly moves over 

rather short distances, probably spending its entire 

life within an area as small as 1 km2 . The fly is 

viviparous, producing a single fully grown larva 

which crawls to a sheltered spot and then pupates 

directly without feeding. The pupal stage lasts for 

several weeks. Spraying with one insecticide application does not effect control because the killed 

adult flies are shortly replaced by a new generation that develops from the sheltered pupae. A second spraying soon after the new crop of offspring 

emerges is usually effective, however (K. J. R. 

Maclennan, oral commun., 1974).

In attempts to eradicate the fly permanently, a 

two-step scheme is being practiced. First, a patch 

of infested forest is isolated by clearing the land 

around the target area. The barrier of cleared land 

needs to be wider than the distance the fly normally migrates, or roughly 1 km. After construction of 

the barrier, the isolated forest patch is sprayed 

with pesticide in the manner noted above. Hopefully, the combination of these two steps will make 

areas of forest habitable that must now be 

avoided.
16 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

Landsat imagery can be used to locate the 

dense stands of trees, especially in areas where 

much of the vegetation has been thinned out by 

human activity. Here, the clumps of dense forest 

are clearly distinguishable from the surrounding 

vegetation if viewed at a season when the open 

mainly cultivated lands are inactive. Figure S-1/A 

shows several areas of dense forest where insecticide spraying might be appropriate.

Bush-burning monitoring

The prime human force in altering vegetation in 

the Sahel appears to be bush burning, especially 

in the areas where annual rainfall exceeds 450 to 

640 mm. The favorite period for burning is during 

the terminal stage of the dry season when, with 

vegetation at maximum dryness, combustion is 

more rapid and less controllable. Fires also burn 

hotter and cause greater damage to woody plants 

and perennial grasses during this period than they 

do at other times (fig. 8). The burning is widespread—from the arable alluvial flats to boulderstrewn slopes and laterite-capped ridges—and 

contributes to the overall harshness of the countryside. Proposals have been made to abolish or at 

least to limit bush burning to the early part of the 

dry season before the vegetation becomes overly 

dry. Such proposals, however, have not been accepted by the pastoral population because they 

use the fires primarily to stimulate early leafing of 

trees and other plants when the livestock are in 

most critical need of green forage after the long 

dry season. This is done in spite of the fact that 

the burning obviously eliminates or reduces the 

availability of dry grass and forbs and the food 

supply during the dry season's crucial terminal 

stage.

FIGURE 7.—Photograph of the White Volta River east of 

Ouagadougou, Upper Volta. Small rapids such as those in the 

middle ground and at the base of the stick dam are a possible 

habitat for black fly (Simulium damnosum) larvae, the insect 

vector responsible for spreading river-blindness disease 

(Onchocerciasis). Entire adult human populations over 30 years 

of age may become blind from this disease. Mud bricks are drying in the sun in the lower right of the picture An earthen dam 

extending across the middle ground has been breached by the 

river.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 17

Bush burning evidently has been practiced in 

Africa for 2,500 years or more (Hopkins, 1965; 

Church, 1968), and it was used widely during the 

dominance of the Rali, Songhai, and Ghana Empires as long ago as 1,000 years (Church, 1968). 

The reasons for burning the vegetation are varied: 

(1) man enjoys watching fire, especially at night, (2) 

man is negligent, allowing camp and cooking fires 

to burn unattended, (3) fires are thought to rid 

areas of parasites such as ticks and, through the 

clearing of the vegetation, of tse-tse flies, (4) clearing sections of the vegetation by burning makes 

cultivation and travel easier, (5) burning drives 

game animals from cover, and their capture is 

made easier, (6) burning stimulates early plant 

growth, (7) burning makes it easier for stock to 

graze on new sprouts, which otherwise would be 

obscured by the old growth, and (8) burning is 

thought to make it easier for the minerals contained in the plants to be returned to the soil. (See 

section on "Accelerated Erosion"; also, Hopkins, 

1965, p. 56).

Landsat imagery has several applications to 

problems where knowledge of the location of recently burned areas is important. For example, in 

the event that attempts are made to limit bush 

burning or to control the season in which it occurs, Landsat imagery could be used during the 

establishment of such programs to detect fire frequency (figs. S-28, S-3). Bush burning is forbidden 

by law in some areas, and Landsat imagery could 

be used to monitor the effectiveness of firesuppression policies.

FIGURE 8.—Unattended unchecked brush fire northwest of 

Bamako, Mali, April 24, 1974. This small fire, burning through an 

area where grassy fuel is sparse, probably has a minimal effect 

on the ecosystem. In other areas where grass is dense, dryseason fires would burn intensely, eliminating much of the 

woody vegetation. Both lightly and severely burned areas 

probably would be visible on Landsat imagery.
18 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

FIGURE 9—Diagrammatic sections of small valleys near Ouagadougou, Upper Volta, and Niamey, Niger, showing distribution of 

laterite, alluvial deposits, areas of accelerated erosion, vegetation, and ground-water conditions.

Vegetation 

————————————————————1———————————————————*<;—————————2—————————afc————3

Wind deflation near village Accelerated sheet erosion

Dug well 

(Permanent water)

Dug well 

(Marginal to dry)

Water table

Deeply weathered basement rocks

A. Diagrammatic section of one of the alluvial flats or of a small valley not having terraces near Ouagadougou.

Vegetation

1

Accelerated erosion 

(includes wind deflation near village)

Gully 

erosion Sheet erosion

Accelerated gully

and sheet erosion

along edge of terrace Dug well 

^(Permanent water)

Dug well

(Marginal to

permanent)

Laterite duricrust over consolidated rocks 

6. Diagrammatic section of a small terraced valley near Bamako.

EXPLANATION Nonarable

I I I I II I I I I I I TIT

Arable gray alluvium, represents extent of 

arable soil minus the areas mainly undergoing sheet erosion where the soil is 

too thin for cultivation

Figure 9A

Yellowish-buff alluvium and equivalents, 

weakly developed laterite at top of unit

Laterite duricrust, generally 1 to 0.5 m 

thick

i i i i i i i i

KEY TO VEGETATION 

Figure 9B

(1) Vegetation a low open forest; variable composition depending 

on history of cultivation and burning; trees both evergreen and 

drought deciduous; grasses important element.

(2) Ground cover of grass all but eliminated where erosion is severe; trees and shrubs of original forest less affected.

(3) Vegetation a low sparse version of that on the alluvial area; 

grasses sparse or only locally abundant.

(1) Many of the same trees as in areas with gray alluviUm,but canopy 

here more open and height lower.

(2) Where cultivated, scattered baobab, shea butter, and mango 

trees remain; on fallow land, vegetation highly variable depending on burning and clearing history; trees, both large-leaved 

evergreen and small-leaved deciduous, dominate; grasses important.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 19

Factors affecting availability of arable land

In the LGA countries, arable soils are developed 

chiefly on deposits of alluvial flats and in small 

valleys (including the ancient dallols, which are 

drainage systems developed during the 

Pleistocene Epoch), bordered mainly by uplands 

capped by laterite duricrusts, on flood-plain 

deposits along the Niger and Volta Rivers, on 

alluvium of the Inland Delta of the Niger River, and 

on eolian deposits of northern Mali and Niger (figs. 

S-4, S-6; table 1).

Alluvial flats and small valleys

The Ouagadougou area was selected to illustrate that mapping of alluvium and laterite is 

feasible through use of Landsat imagery (fig. 

S-28). In an area of gentle planar topography at 

Ouagadougou, the alluvial deposits are thin and lie 

as discontinuous mantles over laterite which is exposed mainly on low ridges and stream channels

(fig. 9/\). To the west of the city is a moderately 

dissected region of flat-topped ridges and intervening small valleys containing thin alluvium. Laterite 

caps the ridges, is present along the slopes of the 

ridges, and extends across the valleys beneath the 

alluvium. Because of conspicuous tonal contrasts, 

the alluvium and laterite in the ridge and valley 

areas are easily distinguished in the imagery. 

However, tonal contrasts between the alluvium and 

laterite are rather indistinct in the gentle flats to 

the east near Ouagadougou and are much more 

difficult to map from the imagery. Admittedly, the 

mapping would be facilitated by the use of a highquality Landsat false-color composite instead of 

the diazochrome overlay with which the writers 

worked.

The writers' brief field study indicates that the 

alluvium in the Ouagadougou area consists of an 

ascending stratigraphic succession of three units 

referred to informally in this report as the brown, 

yellowish-buff, and gray alluvia on the basis of

5 ."' ••' i*. ,M;

\\ > , \ •*! •, f A

FIGURE 10.—A profile of the gray alluvium exposed in a steep-sided channel near Bamako, Mali The upper deposit, A, is modern 

sediment deposited during floods. The middle deposit, B, is represented by an immature soil containing considerable plant 

material as indicated by the dark color. The lower deposit, C, is a slightly consoldiated silt to silty sand which forms the bulk of 

the gray alluvium. The depth of the channel is about 1.5 m. The channel shows fresh scars from recent cutting.
20 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

their characteristic colors. Where the yellowishbuff and gray alluvia are adjacent to the hard 

laterite, they contain only a minor amount of 

coarse detritus derived from the laterite. However, 

the brown alluvium contains a considerable 

amount of coarse material near outcrops of the 

hard laterite and basement rocks. In all localities 

inspected, the yellowish-buff and gray alluvia are 

fine grained, have seemingly consistent lithology, 

and show little variation in grain size. Only the 

gray alluvium is not altered appreciably by laterization, and it is the only one of the three types of 

alluvium that is arable. The other alluvia show 

enough laterization to preclude cultivation.

The gray alluvium, where exposed along many 

channels and gullies, in partially dissected flood 

plains near Ouagadougou and Bamako, consists of 

as least three deposits (fig. 10) which are 

separated by discrete erosion surfaces that probably represent broad channel cutting. All the 

deposits are fine grained, except that the uppermost, deposit A, laid down during the past few 

decades in thicknesses of 0.3 to 0.5 m, is sandier 

than the underlying medial deposit B. Deposit B, 

which generally is less than 1 m thick, consists 

mainly of silt and clay containing some sand and

considerable organic material. It appears to represent deposition in a well-watered flood-plain environment, under somewhat moister conditions 

than those prevailing at present. The lower deposit, C, is more than 3 m thick, is slightly consolidated, and consists of layers ranging from silt 

to silty sand. These layers, in places, show some 

slight development of laterite. Along many 

drainageways, deposit C forms a low terrace a few 

meters high.

The gray and yellowish-buff alluvia and their 

equivalents are widely distributed in the LGA countries, but the brown alluvium was recognized only 

in part of the area near Ouagadougou. In contrast, 

deposits correlative with the gray alluvium are 

present as the uppermost alluvial layer in small 

valleys and alluvial flats throughout the region. 

The yellowish-buff alluvium is recognized along the 

White Volta, Red Volta, and other rivers in Upper 

Volta. Near Bamako, light-brown to yellowish-gray 

alluvium—believed equivalent with the yellowishbuff alluvium—occurs along the Niger River (fig. 

114), along the Baoule River and in small upland 

valleys between these rivers (fig. 98). The alluvium 

along these rivers forms a terrace from 3 m to 

about 5 m high and, except along the Niger River,

FIGURE 11.—Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution of 

laterite, alluvial deposits, terraces, and vegetation zones.

Northwest Vegetation Southeast

2 ————————————————><—————————3 ————————

Very hard laterite cap 

containing considerable 

, siliceous material

Laterite duricrust 

on colluvium

Arable land

Flood-plain alluvium 

not now inundated 

by annual flood

Channel and 

flood-plain 

alluvium in zone

inundated

by annual flood

Laterite duricrust on 

terrace deposits

Niger River

Laterite duricrust buried 

by younger deposits

A, Profile of the valley of the Niger River near Bamako. Maximum relief is about 175 m.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 21

FIGURE 1 1 . — Generalized profiles across the valley of the Niger River near Bamako, Mali, and Niamey, Niger, showing distribution of laterite, 

alluvial deposits, terraces, and vegetation zones — Continued.

Vegetation 

_1 _>|< ————— 2 ——— —— *< —————— 3 ——————

West East

Arable land

Flood-plain alluvium 

not now inundated 

by annual flood

Channel and flood-plain 

alluvium in zone inundated 

by annual flood

Hard ferruginous cap about 

1 m thick over porous 

earthy material (ochre) 

9 to 10 m thick

i i i i i rn\

Discontinuous eolian deposits, 

farmed at many places

Laterite covering terrace of 

rounded gravel deposited by 

Niger River. Niamey is 

situated on terrace

Side channel of Niger 

River, dry for first 

time in spring 1974

Laterite generally 1 m 

thick extends along steep 

slope as low as 15 m above 

river level

Niger River main channel

Dike protecting crops 

from annual floodin

Continental Terminal

3, Profile of the valley of the Niger River near Niamey. Maximum relief is about 100 m.

EXPLANATION

Nonarable

Weathered basement rocks

Arable flood-plain and channel deposits of 

Niger River

Equivalents of the yellowish-buff alluvium; weakly cemented laterite at top 

of unit

Preyellowish-buff alluvium terrace deposits

1.25 to 2 m thick Laterite duricrust 

I I I I I I I I I

About 10 m thick

KEY TO VEGETATION

Figure 11X1

(1) Where soil mantle is thin, plants are confined to fractures and 

pockets of soil; low forest of kapok, shea butter, danya, and 

other trees; grasses are less prevalent than in alluvial areas.

(2) Vegetation is more dense than on alluvial flats or on mesa 

tops of buttes; vegetation not as tall as on the flats; trees 

include kapok, fig, and many others.

(3) Vegetation of areas not now cultivated in various states of 

recovery from farming and clearing; open forest of shea 

butter, locust bean, and many other trees; grasses are prevalent.

Figure 

(1)

(2)

Vegetation in clumps is broken by irregular barren areas; 

dominant plants are drought deciduous shrubs, trees, and 

vines that grow about 6 m maximum height. 

Shrubs to 2 m high dominate; scattered doum palms and 

soapberry trees.

(3) Scattered baobab and mango trees on cultivated lands.
22 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

Table 3.— Distribution of arable land and its relationship to accelerated erosion and gray alluvium

Physiographic position Distribution of gray alluvium

Broad flats

Small valleys 

without terraces

Small valleys 

with terraces

Forms a thin mantle on yellowish-buff alluvium and on laterite; generally is less than 1 m thick, but over wide areas is less than 0.3 m 

thick.

Forms a thin mantle on yellowish-buff alluvium; unit is greater than 

1.5 m thick in central parts of valleys, but is less than 0.3 m on much 

of the gentle slopes along the sides of valleys.

Forms a generally thin somewhat discontinuous deposit on the surfaces of low terraces and on slopes behind low terraces eroded 

from the yellowish-buff alluvium; unit usually underlies narrow 

flood plains that are in front of the low terraces.

Reaches of White Volta and 

Baoule Rivers and other 

streams with conspicuous 

terraces (not including 

the Niger River)

Generally forms thin and discontinuous outcrops on the top of a 

well-developed terrace which is eroded from the yellowish-buff 

alluvium or its equivalents; unit underlies a narrow flood plain in 

front of the terraces, but, at many places, the channel occupies 

nearly all the bottom lands between the terraces.

Valley of Niger River

near Bamako and Niamey

Generally forms thin discontinuous outcrops on terraces eroded from 

the yellowish-buff alluvium and equivalents and on higher terraces 

and slopes; unit covers part of slopes adjacent to the flood-plain 

deposits of the Niger River.

comprises the only conspicuous terrace along 

these streams. The deposits along the Baoule 

River may also be an upstream equivalent of sandy 

clays, 15 m thick along the Senegal River, described by Grove and Warren (1968, p. 196). Near 

Niamey, a light reddish-brown fine-grained alluvium, which is believed to be correlative with the 

yellowish-buff alluvium in the Ouagadougou and 

Bamako areas, forms terraces roughly 8 to 15 m 

above the Niger River. At Niamey, the upper part of 

this alluvium lies on rounded pebble-sized river 

gravels cemented by ferruginous material.

Collectively, the alluvial deposits appear light 

and the laterite appears dark on both Landsat 

black-and-white images and on false-color composites. The younger gray alluvium has a slightly 

lighter tone than the other alluvial units on blackand-white images and is light gray to nearly white 

on the color composites. Thus, its extent, which 

also represents the maximum extent of arable

land, can be roughly delineated. Unfortunately, the 

scale of 1:1,000,000 is too small to permit showing 

the gray alluvium as a separate unit on figure 

S-2B.

In areas where the gray alluvium can be differentiated from the underlying yellowish-buff alluvium, 

a fair estimate of the amount and distribution of 

arable soil can be made, if a sufficient amount of 

field checking is done. Table 3 summarizes some 

of the relationships between the amount of arable 

land and different physiographic occurrences of 

the gray alluvium. In localities where the alluvial 

deposits are not easily distinguishable, only a 

rough estimate can be made of the distribution of 

arable soil. In areas where arable soil maps are 

unavailable, however, any maps, even if only 

roughly defining the areal extent of the soil, would 

have some value. Landsat data could be useful in 

the preparation of such maps.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 23

TABLE 3.—Distribution of arable land and its relationship to accelerated erosion and gray alluvium—Continued

Distribution of arable land Effects of accelerated erosion

Area favorable for cultivation may be small with respect to total area 

covered by the gray alluvium.

Slight sheet erosion and wind deflation around villages and in cultivated or abandoned fields.

Arable land is restricted mainly to central parts of valleys because 

cultivation is limited in areas where the arable soil is greater than 0.3 

m thick.

Predominantly sheet erosion; severe erosion already has taken considerable land out of cultivation; locally, wind deflation is moderate.

Arable land is limited mainly to the flood plains, but part or all of the 

flood plains are inundated by flood flow during the rainy season; in 

other areas, the arable soil is too thin or discontinuous to be of much 

use for farming.

Sheet and gully erosion; gullying and channel dissection locally severe; sheet erosion locally severe accompanied by minor wind 

deflation on top of and on slopes behind the low terraces; the 

accelerated erosion has taken some land out of cultivation.

Little arable soil is available because of generally limited distribution of 

the gray alluvium; reaches of some streams such as the Baoule 

River contain almost no arable soil.

Severe gullying accompanied by sheet erosion has removed much of 

the alluvium and locally forms sharply defined badlands.

Area of arable soil on the gray alluvium is limited, but adjacent floodplain deposits of the Niger River are fertile and are cultivated extensively.

Sheet erosion generally slight to moderate on slopes underlain by the 

gray alluvium; erosion generally slight on the flood-plain deposits of 

the Niger River, except for some gullying along the edges of low 

terraces formed from these deposits.

Channel and flood-plain alluvium along the Niger 

River

Arable alluvial deposits in the valley of the Niger 

River, excluding deposits of the Inland Delta, cover 

thousands of hectares that are easily discerned on 

the Landsat imagery. The deposits comprise two 

broad groups: annually inundated channel and 

flood-plain deposits and earlier flood-plain 

deposits normally not flooded by the Niger River.

The first group includes silty and sandy alluvium 

that occurs along the channel and on adjacent 

flood plains within the zone covered by the annual 

flooding. On some of the flood plains, fields surrounded by dikes to restrain the flood water are 

being cultivated. In the Gao-Niamey area, the river 

channel is braided, consisting of a main channel 

with one or more subchannels. Near Bamako, the 

river occupies one principal channel which is 

flanked by broad sandy flats or beveled bedrock

slopes, both nearly free of vegetation. The channels are conspicuous features on the Landsat images and are easily mapped on any transparent 

overlay (fig. S-4, S-5). Some farming, mainly of 

small vegetable gardens, is practiced along the 

channels during the recession of the annual flood 

and during the low-flow periods (fig. 12). Such 

farming is now minor compared to the amount that 

would be possible if the entire channel system 

was developed systematically. The small garden 

plots have the advantage of being easily developed 

without use of heavy earth-moving equipment.

The second group comprises flood-plain 

alluvium that forms a low terrace (or terraces) not 

now subject to inundation by annual flooding of 

the Niger River. These terraces are broad features 

that extend nearly continuously throughout the 

Gao-Niamey and Bamako areas. The fertile 

alluvium forming the terraces is being utilized for
24 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

field cultivation and tree crops, principally 

mangoes, but it has the potential for more intensive development with water diverted from the 

nearby river. The distribution of this alluvium was 

successfully mapped from Landsat imagery near 

Niamey (fig. S-4, S-5) and Gao; its general 

distribution could be easily mapped from the imagery of other parts of the Niger River basin.

Laterite duricrusts

Hard reddish-brown to blackish-red laterite, in 

which iron oxides or hydrates are the most 

characteristic cementing materials (Cooke and 

Warren, 1973), has formed nearly everywhere in Upper Volta and in the southern parts of Niger and 

Mali. It is present on the summits and slopes of 

tablelands and ridges, on stream terraces, on gentle plains, and beneath alluvial and eolian 

deposits. The laterite is so prevalent that Abdoulaye Sow stated that in Mali "any well having a 

depth of 15 m or more penetrates laterite" (oral 

commun., 1974). The laterite varies widely from 

place to place in hardness, thickness, presence of

detrital material, and composition. In places, it is 

thinly bedded, but, in others, it is massive. The 

detritus incorporated in the laterite is mainly composed of fragments of older laterite deposits, but, 

locally, it also includes rounded pebbles and cobbles of quartz and other dense siliceous rocks. In 

the areas visited by the writers, the laterite 

duricrust is present on Precambrian basement 

rocks near Ouagadougou, on Gres Ordovicien (Ordovician sandstone) near Bamako, on Continental 

Terminal sedimentary rocks near Niamey, on colluvium and alluvium throughout the region, and on 

terrace gravels of rounded siliceous pebbles 

transported by the Niger River near Niamey and 

Gao. Jn general, the laterite near Niamey has a 

greater density, presumably because of a larger 

amount of iron oxides or hydrates than that near 

Ouagadougou and Bamako.

Brief studies indicate differences in the development of the laterite duricrust on the alluvial 

deposits and on the terraces and slopes above the 

Niger River near Bamako and Niamey (fig. 13). The 

flood-plain alluvium of the Niger River and the gray

FIGURE 12.—Small bucket-irrigated vegetable gardens along the bank of the Niger River at Niamey, Niger.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 25

alluvium in small valleys of the uplands do not 

show effects of laterization, whereas the yellowishbuff alluvium and its equivalents are associated 

with a slightly developed laterite that is generally 

weakly cemented and readily erodable. In contrast, 

the laterite comprising the main part of the 

duricrust that mantles slopes and terraces adjacent to or underlying these alluvial deposits is well 

indurated and is resistant to erosion. Near Bamako 

and Niamey, the best developed, most indurated, 

and thickest (about 10 m) laterite occupies the 

summits of the highest buttes and ridges bordering the valley of the Niger River.

The physiographic association of the different 

laterite deposits with buttes, ridges, tablelands, 

and valleys makes it possible to differentiate and 

to map many of the deposits by use of Landsat imagery (figs. S-1^\, S-28). The thickest and most indurated laterite generally is on the summits of 

topographic highs—ridges, buttes, and tablelands. 

These areas appear much darker on the images 

than the areas of laterite on the slopes of these 

features but not as dark as areas where the 

vegetation has been burned recently. The laterite 

areas on the slopes are partly covered by colluvium or alluvium, and, collectively, they have a 

reflectance intermediate between that of the darkappearing topographic highs and the light-appearing alluvial deposits in nearby valleys.

Except for those areas underlain by consolidated rocks, all dark areas on the Landsat images that the writers studied are underlain by 

laterite. The dark laterite is easily distinguishable 

from the light tonal expanses typical of alluvial 

deposits but less easily distinguishable from many 

exposures of consolidated rocks, even if a considerable amount of ground-truth information is 

available. In general, the consolidated rocks are 

slightly lighter than the laterites but darker than 

the alluvial deposits. The consolidated rocks also 

show much more structural deformation than the 

laterite surfaces. Many exposures of the consolidated rocks appear to be "etched" by a pattern 

of closely spaced fractures. Locally, the rocks are 

tilted, and the tilted layers may appear as linear 

and arcuate patterns in Landsat images such as 

that showing a small area near Tombouctou (fig. 

S-6/fy An intensive and detailed examination probably would reveal other diagnostic features that 

would aid in distinguishing the laterite from the 

consolidated rocks in Landsat images.

Accelerated erosion

Many of the areas underlain by alluvial deposits 

are undergoing severe sheet and gully erosion acFIGURE 13.—Laterite in road cuts near Bamako, Mali.

A, Portion of a 10-m-thick laterite layer on the summit of a butte 

175 m above the Niger River. The cut shows layering with individual layers ranging from about 1 to 30 cm thick. Some 

layers are very hard and contain much siliceous material.

fi, Laterite formed on coarse colluvium on the slope of a butte 

about 20 m lower than the laterite shown in figure 13A Included detritus consists of laterite fragments as much as 30 cm in 

diameter.
26 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

FIGURE 14.—Accelerated erosion in Mali and Upper Volta.

A, Advanced sheet erosion in the yellowish-buff alluvium near 

Ouagadougou, Upper Volta.

companied by wind deflation. This erosion unfortunately has resulted in the irreplaceable loss of 

much fertile soil (figs. 68, 10, 14) and already has 

taken from production considerable tracts of cropland and rangeland. The principal areas of accelerated erosion lie in small valleys of the upland 

regions and along stretches of the larger rivers. 

The use of Landsat imagery for identifying such 

severely eroded areas (fig. S-2C) is an important 

tool in analyzing environmental problems confronting the LGA countries.

Gentle slopes of small valleys without terraces 

(fig. 9/A; table 3) have been subjected to severe 

sheet erosion during the past several decades. The 

sheet erosion has removed much of the most fertile part of the gray alluvium. In places, erosion 

has removed this alluvium altogether, thereby 

enlarging the exposures of the nonarable deposits. 

Man's activities, especially near the villages, have 

aided and accelerated the erosion by destroying 

the natural vegetation through excessive grazing, 

trampling (fig. 146), cultivation, and bush burning. 

The removal of the vegetation aids wind deflation 

which is manifested by accumulations of dust 

around small clumps of brushy vegetation growing 

on the nearby slopes and ridges underlain by 

laterite.

In the well-drained terraced valleys (figs. 98, 

14/A, table 3), gully and sheet erosion takes place 

on the slopes of the valleys and along stream 

channels and low terraces toward the centers of 

the valleys. At many places near Ouagadougou 

and Bamako, the valleys are in the process of being deepened by downcutting (figs. 10, 14C). These 

large gullies and steep-sided channels are similar

8, Accelerated erosion along stock trails resulting primarily from 

trampling and browsing near Bamako, Mali. Straw hat toward upper 

right of photograph shows scale. Photograph taken on April 25, 1974, 

near the end of the 1973-74 dry season.

C, Steep-sided channel (similar to arroyos trenched along many 

drainages in Southwestern United States) about 1.5 m deep cut in 

soft alluvium. Scour in channel forms a temporary water hole. Picture 

taken east of Ouagadougou, Upper Volta, on May 13,1974, near the 

beginning of the rainy season.

to the perpendicular walled arroyos or channels 

formed since about 1870 along many drainages in 

the Southwestern United States. The new channels 

display freshly cut scars, most ranging in depth 

from 1.5 to 2 m. Generally, the channels are discontinuous and, fortunately, have not yet caused
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 27

extensive damage to cultivated land. The channel 

downcutting would be more extensive if it were not 

for low stream gradients which tend to retard and 

localize the process. At places near Niamey, 

gullies and well-developed vertical walled channels 

are present along the sides of the Niger River 

valley. In this vicinity, the channels have been 

readily incised in loose sandy alluvial deposits.

Many areas of badlands, scored by severe gully 

erosion, border the White Volta, the Baoule, and 

other rivers in southern Mali and Upper Volta and 

are present at places near the Niger River in Niger. 

Groups of headward-cutting gullies are advancing 

into terraces and slopes formed principally of the 

easily erodible yellowish-buff alluvium and its 

equivalents. In places, the terraces have been 

nearly obliterated by the gullying. In most places, 

severe sheet erosion accompanies the gullying.

The areas of accelerated erosion are large 

enough to be easily identified on black-and-white 

Landsat images or on false-color composites (figs. 

S-1X\, S-2C). The color composites enhance the 

contrast between the severely and slightly eroded 

areas, thereby facilitating their mapping. From onsite inspection, the writers observed that the 

lightest areas on the images, appearing as 

"bright" areas within alluvium, indicate severe erosional activity. The bright areas generally appear 

as spots or blotches or combine in a somewhat 

elongate or linear pattern along the eroded edges 

of terraces.

Annual flood of the Niger River

The Niger River, the lifeline of Mali, Niger, and 

much of Nigeria, heads in the highlands of Guinea 

and the Ivory Coast. Its flow is sustained by precipitation that occurs only during the rainy highsun months (May-October). The river flows through 

a wide plain stretching from Mopti to the Detroit 

Soudanis (Sudanese Narrows) near Gao. This plain 

of low relief is laced with waterways and is called 

the Inland Delta of the Niger. The Niger River 

within the Inland Delta includes a main channel 

and many anastomosing distributary channels 

(fig. S-6/\), some of which carry water only during 

high flows. Near Tombouctou, several distributary 

or overflow channels extend northward and terminate in a maze of active sand dunes along the 

southern margin of the Sahara (fig. S-68). 

Throughout the centuries, the shifting of floodwaters in these distributaries has determined 

where people live and the use they made of the 

land in the Inland Delta.

The flow of the Niger River is sustained during 

the long dry season (10 months at Tombouctou) by

the precipitation that fell during the previous rainy 

season. Part of this precipitation does not run off 

immediately and is not evaporated but directly infiltrates the land surface to recharge the groundwater reservoir. Another important recharge to the 

ground-water reservoir occurs during the annual 

flood when large areas are inundated by the Niger 

for weeks at a time. Slow drainage from the 

ground-water reservoir helps maintain the river's 

flow during the dry season. The time of minimum 

flow of the river is in April at Bamako and in June 

at Niamey. From 1954 to 1972, the mean annual 

discharge ranged from a high of 2,063 cubic 

meters per second in 1969 to a low of 1,083 m3/s in 

1972 (table 4). Beginning in 1970, the mean annual 

flow of the river has been consistently lower, a 

manifestation of the major drought cycle that has 

affected much of Sub-Saharan Africa for the past 5 

years.

The Niger River has a large annual flood that 

moves slowly downstream and takes several 

months to travel from Bamako to Gao, an airline 

distance of about 1,300 km. The crest of the 

1972-73 annual flood after the 1972 rainy season 

passed Bamako in September, Mopti in October, 

Tombouctou at the end of November and the 

beginning of December, and Gao near the end of 

December 1972 (data from RAF/71-1283, Flood and 

Drought Forecasting and Warning System in the

TABLE 4.—Mean annual discharge at two gaging stations in the 

Niger River System, southern Mali

[Data from RAF/71-1283, Flood and Drought Forecasting and Warning System in the 

Niger River Basin, World Meteorological Organization, Bamako, Mali]

Mean annual discharge 

(cubic rmtere par second)

Year

1972 _____________ _

1971 _____ _______________

1970 _ ___ _ _______ ._

1969 _ _ _ . _ __ _

1968 ___ _ _ _____

1967 _ _ __ _ _

1966

1965 _______________________

1964

1963 _ _ ________________

1962 ____ ___ _

1961 _ _____

1960 _ __________ ____

1959 _ _____

1958 _ _ _ ______

1957 _ _ ______ _

1956

1955 ______________________

1954 _______ __________

Nig«r Rlvw

at

Bamako

___ 1,083

__ __ 1,261

1,157

2,063

____ 1,459

_ _ 1,912

___ 1,438

____ 1,502

_ _ 1,566

___ 1,559

1,832

__ _ __ 1,275

___ 1,657

_ _ 1,539

1,502

1,978

____ 1,365

1,981

_ __ _ 1,969

Ban) Rlvw

at

Moptf

694

1,196

1,139

1,620

1,173

1,333

1,472

1,316

1,622

1,328

1,617

1,194

1,250

1,284

1,483

1,427

1,264

1,693

1,636
28 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

Niger River Basin, World Meteorological Organization, Bamako, Mali). The progress of the flood 

crest is especially slow through the Inland Delta 

where the waters spread across an area about 100 

km wide.

Many investigators familiar with the Niger River 

have suggested that its annual flood could be 

monitored by the use of the Landsat imagery. 

Figure S-QA was prepared to show the feasibility 

of monitoring and mapping the annual flood from 

images. This image shows part of the Inland Delta 

near Tombouctou and the extent of the flood on 

October 12, 1972, a few weeks before the maximum flood stage or extent in this area.

Ground-water development in fractured rocks

Many consolidated rock terrains in the LGA 

region are crisscrossed by extensive networks of 

linear features that can be mapped from aerial 

photographs as well as from Landsat imagery (fig. 

S-18). These linear features indicate that the rocks 

are fractured intensively in places, such as at the 

intersections of the main linear features. In such 

places, the consolidated rocks may have a sufficient secondary permeability to contain dependable supplies of ground water that could be tapped 

by drilled wells.

In the area shown on figure S-1 of Bamako 

vicinity, the consolidated rocks are composed 

mainly of tightly cemented sandstone referred to 

by Archambault (1960) as the Gres Ordovicien 

(table 1). These rocks are nearly horizontal or dip 

gently to the north and northeast. Some of the 

sandstone members contain a few rounded quartz 

pebbles, and, at one exposure about 48 km north 

of Bamako on the road leading to Didieni, the 

sandstone contains some coarse pebble conglomerate. At Bamako, part of the sandstone shows 

some ripple marks and well-formed generally 

medium-scale current-bedding dipping to the east 

and northeast that indicates that it was laid down 

in generally eastward-flowing streams. At Koulikoro, a sandstone member that also has eastdipping current beds and that probably is the same 

unit as the one at Bamako is exposed at the base 

of a high bluff. Above this sandstone member is 

another sandstone that has large-scale high-angle 

crossbedding dipping westward. The crossbedding 

and the generally uniform fine to medium grain 

size suggest that the sandstone was deposited by 

winds blowing generally from the east.

Yields of wells penetrating the relatively unfractured parts of the Gres Ordovicien probably would 

be small at best and sufficient only for supplying

stock and small villages, but the yields of wells 

drilled into the fractured zones of the sandstone 

would be considerable and perhaps could supply 

comparatively large communities with water. 

Evidence that fractures locally influence the occurrence and movement of ground water is demonstrated in two ravines at Bamako. Ground water 

discharging from fractures in the sandstone sustains springs in the Ledo Canyon ravine and, as 

recently as 20 years ago, sustained a small flow in 

the shallow ravine near the Bamako Zoo (Abdoulaye Sow, oral commun., 1974).

Storage and movement of ground water is clearly indicated along the large linear features in the 

Baoul6 River area northwest of Bamako (northwestern part of fig. S-18). The writers inspected 

this area from a light plane flying less than 200 m 

above land surface on May 2, 1974, near the end of 

the 1973-74 dry season. The specific trace of some 

of the linear features was observed to extend for 

more than 30 km. Differential erosion of the fractured rocks along the linear features has carved 

small narrow somewhat wedge-shaped canyons 

along the edges of buttes and ridges. At other 

places that have a gentle topography, many of the 

linear features support a growth of vegetation 

denser than that on the relatively unfractured 

rocks away from these features (fig. 15). Patches 

of verdant vegetation were observed at intersections of the large linear features. Inspection from 

the air disclosed that the channel of the Baoul6 

River above its confluence with the Bakoye River 

in the area of Pare National de la Boucle de 

Baoulg contains large pools of water and short 

reaches of seemingly perennial flow downstream 

from the points where the river crosses large linear 

features; the other reaches of the river were dry at 

this time. As far as could be ascertained from air 

reconnaissance, the water in the river's channel is 

maintained by the discharge of ground water from 

the fractured rocks along linear features.

Landsat images are especially useful for mapping the main linear features (fig. S-18). In areas 

of high relief, where differential erosion of the 

rocks is great, the linear pattern is easily discerned, but, in other areas, such as plains 

underlain by laterite, lineation is much fainter. The 

linear network provides a key to fracture trends 

and thus to the possible paths of ground-water 

movement in the consolidated rocks. Study of the 

lineations may point to favorable places where 

ground-water supplies in the consolidated rocks 

could be developed. Most favorable places would 

be along lineations representing fractured zones 

and especially at points of intersecting lineations.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 29

FIGURE 15.—Low-altitude oblique aerial photograph showing fractures, indicated by arrows, in the Gres Ordovicien (Ordivician sandstone) near the Baoule River northwest of Bamako, Mali. The photograph was taken from a light aircraft on May 2, 1974, near the 

end of the 1973-74 dry season. Dense vegetation in the niche carved in the large fracture suggests presence of permanent ground 

water at shallow depth.

Evaluation and Utilization of Landsat 

Imagery

Landsat imagery provides a valuable source of 

information required for solving important resource 

problems of the developing countries in semiarid 

and arid regions. It displays a view that is unique 

in its comprehensiveness and its repeatability and 

gives a quick, convenient, and inexpensive means 

of examining the Earth's surface—a means that 

otherwise is not available to investigators and 

planners in the Sahelian countries. In essence, the 

imagery extends the vision of the investigator or 

planner by furnishing him a synoptic picture of the 

terrain, drainage network, vegetation, and geohydrology of a particular region. Given this general 

framework of information, the investigator may 

then choose, if warranted, more detailed methods 

of examination. Proper interpretation of the imagery depends, in considerable measure, upon

adequate onsite verification and upon the investigator's knowledge and experience in dealing with 

environmental problems. An important attribute of 

the imagery is its simplicity—interpretation of the 

imagery does not require sophisticated photogrammetric equipment or specially trained photointerpreters.

As with any remote-sensing technique, the use 

of Landsat imagery has certain limitations imposed by environmental conditions. The most commonly encountered conditions in West Africa that 

impose such limitations are as follows:

1. The general evenness of the West African landscape and the lack of sharp tonal contrast in 

the imagery limit the usefulness of the imagery for mapping detail, even with excellent 

ground control.

2. The imagery provides a view of the land surface 

only; thus, surficial features such as the widespread laterite duricrust or dune-sand
30 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

mantles may conceal the underlying rocks 

and obscure many geohydrologic details.

3. Activities of man such as clearing, overgrazing, 

bush burning, cultivation of fields, and construction near villages may obscure natural 

vegetative and geohydrologic boundaries.

4. In West Africa, the widespread atmospheric 

haze that is present during much of the dry 

season hampers Earth-observation studies to 

some extent. During the rainy season, extensive cloud cover poses an additional problem. 

In spite of these limitations, the imagery can be 

usefully applied (1) to provide a general overview 

of a region as well as to serve as base maps in 

regions where few or no good ground surveys exist, (2) to provide a method for surveying, cataloging, and mapping Earth-resources information, (3) 

to provide a basis for repetitive inventorying and 

monitoring transient environmental changes, and 

(4) to aid in solving special problems of diseasevector control or human activity.

The Landsat images give an excellent visual impression of the landscape, including cultural and 

environmental features. The images can be 

grouped in mosaics to provide broad regional or 

national coverage. Such image maps can be effectively used as base maps showing the major drainage systems and reservoirs and the location and 

area! distribution of other natural and cultural 

features.

Landsat images give excellent synoptic views of 

faults, fractures, and other linear geologic features 

and of the lithologies of older consolidated sedimentary and basement rocks, where they are exposed. Because of the concealment of these rocks

in much of the LGA region and of the generally 

low relief, the Landsat images are more applicable 

to mapping of younger surficial deposits. Accompanied by onsite investigation, the images form an 

excellent means for preparing small-scale maps 

showing flood plains, dunes, alluvial deposits, laterite duricrust, and accelerated sheet and gully 

erosion. Areas of arable land can also be determined because of the association of such areas 

with certain alluvial deposits. In some of the LGA 

countries, such as parts of Niger, where accurate 

and complete geologic maps are available, relatively little new information concerning rock distribution or composition will probably be obtained 

from the imagery. Nevertheless, in most places, regardless of the previous geologic map coverage, 

analysis of the imagery can contribute to the 

knowledge of the details of geologic features previously identified by conventional methods. When 

identified in the imagery, these features provide 

additional insight into the broad geologic configuration of the region.

Landsat imagery can be used directly and indirectly to examine hydrologic features of the 

Sahel. Streams, lakes, and reservoirs are examples 

of directly observed features. Other features can 

be largely inferred from the vegetation or geology. 

Some hydrologic features that may be indentified 

indirectly include presumed permeable zones 

along the main linear structural features and at the 

points of intersection of these features, areas of 

shallow ground water in flood plains and in dallols 

(ancient drainages, fig. 16), and sites suitable for 

surface-water storage or for catchments.

Arable land

Terrace formed from equivalent 

of yellowish-buff alluvium 

dissected by gullies

Laterite 

duricrust

Present stream channel/ 

of Dallol Bosso

Low terrace formed from 

alluvium of Dallol Bosso

1

FIGURE 16.—Diagrammatic cross section of Dallol Bosso near Niamey, Niger. The length of section is about 7 km. The width of 

alluvium of Dallol Bosso is about 5 km. This section shows about 100 m of vertical relief. Because of almost complete cultivation, 

the floor of the Dallol Bosso near Birni-Ngabure supports only scattered trees that have been preserved in the clearing process. 

Prominent among these trees are the doum palm and the baobab tree. The uplands, only sparsely cultivated because of laterite 

duricrust, support an open forest of varying composition depending upon soils and history of burning and clearing.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 31

Many transient environmental features showing 

seasonal change can be observed with repetitive 

Landsat imagery. These features are principally 

vegetative, but they may have hydrologic implications. Seasonal change in foliation of vegetation is 

a commonly observed phenomenon on Landsat imagery. Seasonal differences are especially marked 

in regions that have fluctuating rainfall and temperatures. The use of Landsat imagery to measure 

regional crop yields during the early part of the 

rainy season is probably one of the most important 

applications.

Transient hydrologic phenomena such as the 

stages of rivers in floods or at low flow, intermittent streams, fluctuating lake levels, reservoirs, 

or small ponds can all be identified and their 

general stages monitored by repetitive imagery. 

The annual floods of the Niger, Senegal, and Volta 

Rivers and their larger tributaries should be rather 

easy to follow as the floods progress slowly downstream. Within the Inland Delta of the Niger River,

knowledge of the exact area inundated by floodwater would be important information upon which 

to base yield estimates for crops grown after the 

flood.

Repetitive imagery may help locate shallow 

ground-water bodies that could provide a water 

supply during part of the dry season. Patches of 

lush vegetation often indicate areas of shallow 

ground water, particularly along intermittent 

streams and in small alluviated valleys, where 

ground water is discharged. All dark spots or areas 

shown on bands 6 and 7 of Landsat imagery are 

worth checking to determine if they are "damp" 

areas, where the water table is near the land surface, or ephemeral lakes or ponds that may not be 

related to the presence or discharge of ground 

water.

Landsat imagery can be used to assist in 

disease-vector control programs such as the tsetse fly and river-blindness control programs.
32 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

Landsat Imagery With Explanations

The following section presents analysis of six 

Landsat images S-1 to S-6 (fig. 17). The analyses 

of two images were originally made on false-color 

composites of multispectral scanner (MSS) bands 

4, 5, and 7 prepared at the EROS Data Center, but

the analyses of the remaining four images were 

made by using diazochrome overlays for which 

band 4 was reproduced in yellow, band 5 in 

magenta, and band 7 in cyan. Comparisons also 

were made between the false-color composites or 

diazochrome overlays and the black-and-white 

frames of all four MSS bands.

20°

18°

2°

1RO Nioro du Sahel /

1f?V\ _ _ \ fl____MAURITANIA /

MALI "" '

Names and boundary 

representation are not 

necessarily authoritative

100 200 300 400 500 KILOMETERS

_J____i____I____I , i______,

0 100 200 300 400 500 MILES 

FIGURE 17.—Areas represented by the six selected Landsat images of Mali, Niger, and Upper Volta that are evaluated in this report.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 33

IW008-30 W008-00I W007-30I

W008-30! 

I7NOV72 C N13-0J/U008-00 N Ni2-59AJ007-57 tlSS

U008-00I W007-30I 

R SUN ELa? BZI38 188-1627-R-I-N-D-2L NflSfl ERTS E-1117-10232-5 01

FIGURE S-1.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1117-10232, November 17, 1972) showing the region 

near Bamako, Mali. This image shows an excellent panorama of the geohydrologic setting; the drainage network, including the 

Niger River valley and adjoining ridges and buttes; the vegetation; and many features of the small valleys and alluvial flats. 

(Approximate scale is 1:1,000,000.)
34 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

IMW8-38 W807-38I

14808-381

N M 2-S3/U087- R SUN 188-1627-FM-N-D-2L NRSB ERTS E-l 117-10232-5

FIGURE S-1.—False-color composite Landsat images (MSS bands 4, 5, and 7 of 1117-10232, November 17, 1972) showing the region near 

Bamako, Mali. This image shows an excellent panorama of the geohydrologic setting; the drainage network, including the Niger River valley 

and adjoining ridges and buttes; the vegetation; and many features of the small valleys and alluvial flats—Continued. 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 35

EXPLANATION S-1A

This overlay shows the general distribution of laterite, alluvium, 

and areas of accelerated erosion (see arrows and also figure 

S-2) and illustrates how the imagery can aid the tse-tse fly 

control program.

Alluvial deposits (the gray alluvium and equivalents of the 

yellowish-buff alluvium) constitute the lightareas of the image. 

In well-drained valleys, the gray alluvium occupies narrow 

flood plains and appears as a reddish-brown band of vegetation. The lightest areas are those alluvial areas undergoing 

accelerated erosion. The laterite-capped buttes and ridges and 

the indurated Ordovician (Gres Ordovicien) sandstone that 

form these features appear dark. Laterite, partly covered by 

thin alluvial deposits on slopes and in areas of low relief, has an 

intermediatetone. The irregulardarkareas, showing little relation to the topography, are burned areas.

Tse-tse flies require shade during the warm part of the day and 

seem to prefer large clumps of trees orcontinuous forest rather 

than individual trees. Toward the northern edge of the fly's 

range, dense groves of trees large enough to support tse-tse 

populations occur only in special habitats. In the Bamako area, 

one such habitat of dense groves is along the flanks of lateritecapped mesas. Here one might expect isolated pockets of tsetse flies. Toward the lower left corner of the image, in an area 

where rainfall probably reaches a maximum for the area of the 

frame, some of the buttes attain altitudes of more than 650 m. 

Hillslope forests, which developed because of the greater rainfall of these elevated lands, are possible habitats of tse-tse flies 

and appear as thin red patches fringing the elevated lateritecapped summit areas (see arrows). In the vicinity of Bamako 

and northward, where altitudes are 250 to 300 m lower, the 

hillslope forests are not developed.

EXPLANATION S-1fi

Landsat imagery is extremely useful for mapping linear structural features. This overlay shows the linear features that may 

affect the movement and storage of ground water in the consolidated rocks (Gres Ordovicien) near Bamako. The linear features, indicating to a large extent valleys, drainage lines, and 

ridges, trend as straight or slightly curved lines.

Major linear structural features 

Minor linear structural features

Intersections of the major linear structures seem to be the most 

promising places for obtaining adequate ground-water 

supplies from deeply drilled wells.
36 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

W002-30I W882-08I

2 -301

P R SUN ELK OZI3I -1 CRT! I tf

FIGURE S-2.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095-10000, October 28, 1972) showing the area near 

Ouagadougou, Upper Volta. This image was used to map lakes, reservoirs, laterite, alluvium, and areas of accelerated erosion. 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 37

EXPLANATION S-24

In the southern part of image 1095-10000, several lakes or 

reservoirs appear blue, if muddy, and dark purple, if clear. 

Several lakes shown on a map of the area (Army Map Service 

map 1501XND3015; ground-checked from 1959 to 1964; scale 

1:250,000) are not visible on the Landsat image, presumably 

because they were dry at the time of the satellite overpass. 

Other lakes seen on the image but absent from the map are 

presumably new or were missed at the time ground-checking 

for the map was done. To be visible on Landsat images, a lake 

must be more than about 250 m in diameter. Some of the lakes 

are ringed by white, indicating that grazing and erosion are 

probably severe near the lake. The large lake near 

Ouagadougou does not have a white ring because of the dense 

vegetation that grows along its shore.

Spillways for lakes such as those seen on this image may be 

breeding sites for the fly, Simulium damnosum, which carries 

river-blindness disease (Tomiche, 1974). Because these bodies 

of water are often temporary and because new stock ponds are 

constantly being constructed, as for example, in a Peace Corps 

program in Upper Volta, Landsat imagery could serve as a 

means for locating these sites, which are potential loci for the 

spread of river blindness.

The tonal contract between the laterite and alluvium is excellent 

in the northwestern two-thirds of the image where the land has 

mode rate relief. In the area of low relief in the southeastern part 

of the image near Ouagadougou, the contrast is poor, making 

differentiation between the areas underlain by laterite or 

alluvium difficult to discern with either the black-and-white 

images or with the false-color composite. Areas of low relief 

may be beyond the limit of Landsat capabilities because of the 

slight tonal differences in soil-surface color occurring there.

The laterite appears dark on the false-color composite or on the 

black-and-white bands, of which MSS band 7 is the most useful 

for distinguishing the laterite from the alluvium. The areas 

underlain by alluvium appear as different light tones, 

depending upon the amount of vegetation, the amount of 

foliage at the time of the overpass, the amount of accelerated 

erosion, and the distribution of the different alluvial deposits. 

The gray alluvium appears slightly lighter than the other 

alluvial deposits, but not as light where it orthe other deposits 

are being subjected to accelerated erosion.

Several recently burned areas are visible as dark splotches on the 

image. These splotches may be distinguished from clear lakes 

because the burned areas appear less blue and are not confined 

to low positions in the terrain. (See also figure S-3.)

The area underlain by the gray alluvium represents the only 

available arable land. In much of this area, however, the gray 

alluvium is too thin for extensive cultivation (table 3), partly as 

a result of accelerated erosion. The general distribution of the 

gray alluvium and of the arable land can be coarsely outlined 

from this image. In valleys where the gray alluvium underlies a 

narrow flood plain along the main streams and is subjacent to 

terraces formed from the yellowish-buff alluvium, the flood 

plain may support relatively lush vegetation that appears dark 

on MSS band 5 and reddish-brown on the false-color 

composite. In the alluvial flats and in valleys lacking terraces, 

the gray alluvium extends nearly across the alluviated area.
38 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

HW2-30I W002-B0I M-3BI

*•»*>.*

t.

____ IU003-TO

260CT72 C NI2-58/Ue02-l5 N NI2-56/W002-II

LtOCt? - dfl I

R SUN EL52 RZI31 188-J320-R-1-N-D-2L NflSfl ERTS E-li85-He08-S

FIGURE S-2.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095-10000, October 28, 1972) showing the area near 

Ouagadougou, Upper Volta. This image was used to map lakes, reservoirs, laterite, alluvium, and areas of accelerated erosion—Continued. 

(Approximate scale is 1:1,000,000.)
EXPLANATION S-2B

Figure S-2A shows the preliminary results of mapping of the 

laterite and alluvial deposits in a moderately to slightly dissected region shown in the east-central part of this image.

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 39

Area underlain chiefly by laterite duricrust generally more than 2 

m thick on summits of low narrow mesas and ridges and on 

their slopes. Most mesas and ridges are too small for the 

laterite on their summits to be separated from that on their 

slopes.

Area underlain chiefly by the brown, yellowish-buff, and gray 

alluvia. Includes small outcrops of laterite too small to show 

separately.

Area consisting of gentle slopes underlain by laterite duricrust 

and alluvial flats and valleys underlain by the brown, 

yellowish-buff, and gray alluvia. Locally, the alluvial deposits 

may exceed 25 percent of the total a rea. The outcrops of laterite 

and alluvia are too small or too irregular to show separately at 

this scale.

Gentle plain near Ouagadougou underlain by laterite duricrust 

and thin alluvium consisting of the brown, yellowish-buff, and 

gray alluvia. Although the gray alluvium may cover more than 

50 percent of the area, the deposit is as thin as 20 cm thick in 

some places.
40 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

M882-38I

ZSOCT72 C IS N Nl2-56A«2-U

-381

R SUN EL52 RZ13I 188-I328-R-M4=D-2L NRSfl ERTS £-1895-18888-3 flf

FIGURE S-2— False-color composite Landsat image (MSS bands 4, 5, and 7 of 1095-10000, October 28, 1972) showing the area near 

Ouagadougou, Upper Volta. This image was used to map lakes, reservoirs, laterite, alluvium, and areas of accelerated erosion—Continued 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 41

EXPLANATION S-2C

Areas of accelerated erosion can be recognized easily on the 

Landsat black-and-white images or false-color composites.

Dots represent areas undergoing severe sheet erosion. Includes 

small areas of headward gullying along terraces of the larger 

streams and areas of scattered severely sheet-eroded alluvium 

overlying laterite, both of which are too small to be shown at 

this scale.

•ttffltfflf

Area of extensive headward gullying along channels and along 

terraces formed from the yellowish-buff alluvium.

On this image, areas of accelerated erosion have the greatest 

reflectance and appear as light spots, white splotches, or as 

features that are irregular, somewhat elongated, or linear. The 

linear or elongate features represent areas of severe sheet and 

gully erosion along terraces, whereas the other features are 

principally areas of severe sheet erosion. The width, depth, or 

the distribution of the gullies cannot be determined from the 

Landsat images and must be obtained from onsite inspections 

or from large-scale aerial photographs.
42 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

IN0I5-38 114003-30 wees-00i W008-30I

d area

8 ned ai><:

Burned area

"New village? .

fsfew village?

Atiaodcw^d village?

ondoned village*

IU010-00 U009-30I UI003-00I 

MflPRTS C N|a-3a/W009-l5 N NI«-33-^4009-B9 PtSS 5 R SUN EL57 RZ097 !88-36a9-N-I-N-D-2L NRSR ERTS E-1262-10290-5 01

FIGURE S-3.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1262-10290, April 11, 1973) showing the Baoule River 

country northwest of Bamako, Mali. The image shows burned areas and the distribution of villages. 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 43

EXPLANATION S-3

Villages can be seen easily on this Landsat image, which shows 

the region near Nioro du Sahel and Sefe, Mali. The light areas 

are land from which much of the vegetation has been removed 

by farming and grazing. These denuded areas reflect light 

throughout all spectral bands to which Landsat is sensitive. 

Villages are usually somewhere within the denuded areas. 

Some trails also appear as light-colored strips, presumably 

because the vegetation along them has been thinned out. To 

verify that the pattern of light spots seen in the image is 

produced by villages, a map of all villages within the area 

shown in this image was drawn from Army Map Service map 

130XND29 (scale 1:1,000,000). When compared with the 

Landsat image, the correspondence between the location of 

the villages shown on the map and light areas in the image is 

close, although several villages not on the map appear in the 

image. Conversely, several villages noted on the map appear 

from their appearance on the image to have been abandoned.

Several large dark areas seen in this image were not in an August 

1973 image 1028-10274 (not shown). Although the writers did 

not visit these areas, they are probably the result of bush fires. 

In comparing the April 11, 1973, image to an April 29, 1973,

image (not shown), additional dark spots were found in the 

latter image. These spots are presumably areas which were 

burned over in the 18-day period between the two satellite 

overpasses.

If attempts are made to limit bushburning orto limit it to a given 

season, Landsat imagery could be used to detect and monitor 

fires. North of the area shown in this image, bushburning is 

forbidden bylaw in some places, and satellite imagery could be 

used to aid in administering the bushburning supression policy 

there.

The Baoule River is barely visible in this image, and inspection of 

the area revealed the reason. This, and many other streams in 

the area, lack the fringing forest that is typical of watercourses 

in the Sahara and other deserts of the world. Instead of a 

concentration of these typical plants, streamcourses in this 

region support vegetation that is little different from the vegetation of the surrounding area. As a consequence, the streams 

are not accentuated on Landsat images and are difficult to 

detect. The absence of a concentration of characteristic plant 

types along watercourses is typical of many Savanna streams 

and may be the result of burning (Grove, 1973).
44 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

t«BI

,

g^^——^*Smm %as^

Lake or Reservoir 

(Bell)

or Reservoir

-—• ""-'r;-^ ^-iMviU^''-^'-^ "-"*""" I

\ Lake or \ 

. * \ Reservoir \

Apssolo) \ /

^

A

^L , f «.•.-.•• -•••••::•:•:••'. ^——-<yr±::*-'-- -

IINOV72 C N-O-JL NflSfl ERTS E-1111 ei

FIGURE S-4.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1111-09483, November 11, 1972) of the area near 

Tillabery, Niger, showing arable alluvium along the Niger River, the principal dune deposits, and small dark areas (A) and drainage 

that may indicate sources of shallow ground-water supplies. (Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 45

EXPLANATION S-4

Small dark areas showing on MSS bands 5, 6, or 7 indicate 

vegetation and possibly damp areas that may indicate shallow 

ground water. Images 1111-09483 (November 11, 1972) and 

1271-09484 (May 10,1973, which is not shown) were also used 

to compare conditions at the beginning and near the end of the 

1972-73 dry season. Some of the damp areas, if present, may 

contain water too salty for human or livestock use because 

most potable shallow ground-water sources probably would 

already have been developed by the local inhabitants (John 

Buursink, oral commun., 1974). A cursory inspection from a 

commercial jetliner revealed that some of the dark areas 

appear to be depressions—lined or underlain by dark clayey 

deposits—which probably act as tanks holding water 

temporarily. A few of the dark areas contained ponds as of 

November 11, 1974, and are so noted on the figure.

f

Major drainageways that appear 

Aas dark strips on MSS bands 5,6, 

or 7 of images 1111-09483 and 1271-09484. The dark strips 

indicate mainly riparian vegetation whose growth is 

dependent upon ephemeral streamflow and bank and channel 

storage. In some places, shallow ground-water supplies might 

be developed along these drainages.

Channel and flood-plain alluvium undifferentiated along the 

Niger River. If developed intensively, farm products grown on 

these deposits could help in alleviating food shortages that 

occur from time to time in Mali and Niger.

Braided channel of the Niger River.

Area of extensive eolian deposits (including deposits forming 

sand stripes). Includes some alluvial deposits. Thickness not 

known.

Area of alluvium, laterite, and consolidated rocks generally not 

overlain by extensive eolian deposits. Includes the Continental 

Terminal valley fill deposits.
46 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

E002-00I EB02-38I EkWJ-WI—""

*

0.

I /

ss».,. 

-

Niamey

E001-3 H N(4-30 IN0I3-38 7Ci| N NI4 «iE0?2-ae

O•o

CD

O.

>-^-- .•$ Mesas 

£ ^gv...:/i capped 

%*>| by

%ii laterite

P QiN FI4R O7I37

E002-30I ^-ft- J -M-n-71 NfKfl FRTS P- 11 IB-«<M?4-5 fl!

FIGURE S-5—Part of Landsat frame 1110-09424, MSS band 5, showing alluvial deposits of the Dallol Bosso and the Niger River 

near Niamey, Niger. (Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 47

EXPLANATION S-5

Some of the most interesting features of the northern Savanna 

and southern Sahara, readily identified and mapped from the 

Landsat imagery, are the dallols, which represent ancient and 

now largely unused drainage systems developed during more 

humid climatic conditions of the Pleistocene Epoch. The dallols 

are well-known physiographic features; they are shown on the 

geologic map of Niger (Greigert and Pougnet, 1965) and on 

other maps. The Landsat data provide a convenient method for 

quickly obtaining information about the size, distribution, and, 

perhaps, the vegetation and soil cover of the dallols. Only 

Dallol Bosso, an ancient valley east of Niamey, was inspected 

during the present investigation (fig. 16). There the alluvium is 

extensively hand cultivated and grazed. The presence of dug 

wells indicates that considerable ground water occurs at a 

shallow depth along the floor of the dallol, although the 

amount of water in storage and its chemical quality is not 

known. Comprehensive investigations, including some test 

drilling, would determine the extent to which the dallols can be 

developed for agriculture.

Alluvial deposits of Dallol Bosso drainage system. The dallols of 

West Africa drained generally southward toward the Niger 

River or interior lowlands during Late Pleistocene time.

Channel and flood-plain alluvium undifferentiated along the 

Niger River.

Braided channel of the Niger River.
48 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

FIGURE S-6.—False-color composite Landsat image (MSS bands 4, 5, and 7 of 1079-10102, October 10, 1972) showing part of the Inland Delta of the Niger River near Tombouctou, Mali. The image provides a spectacular view of the below-normal 1972-73 flood of 

the Niger River, lakes and ponds fed by overflow distributaries of the river, broad lowlands or depressions of the Inland Delta that 

are subject to inundation by normal or above-normal floods, and extensive dune tracts composed of stabilized and active dunes. 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 49

EXPLANATION S-6A

An effective application of the Landsat imagery is the mapping of 

floods. From this image, the 1972 annual flood of the Niger 

River can be readily mapped. Muddy flood waters (blue) are 

especially conspicuous on the false-color composite and can 

also be seen clearly on black-and-white images of MSS bands 

5, 6, or 7.

Extent of the annual flood of the Niger River on October 10,1972. 

The maximum width of the inundated area shown atthe bottom 

of the image is 85 km.

Small distributary channels of the Niger River.

Main lowland areas of the Inland Delta subject to inundation 

when flood crest passes. Outside boundary is indicated by a 

long dash (——).

Approximate area mainly underlain by unconsolidated surficial 

deposits of dune sand and alluvium of the Inland Delta.

Approximate area mainly underlain by consolidated sedimentary 

rocks.

Highly generalized contact between sedimentary rocks and 

surficial deposits as mapped from the Landsat imagery.

Direction of strike of folded sedimentary rocks.

Area masked by clouds and shadows.
50 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

WWW-301 HW3-WI

I00CT72 C NI5-

FIGURE S-6— False-color composite Landsat image (MSS bands 4, 5, and 7 of 1079-10102, October 10, 1972) showing part of the Inland 

Delta of the Niger River near Tombouctou, Mali. The image provides a spectacular view of the below-normal 1972-73 flood of the Niger River, 

lakes and ponds fed by overflow distributaries of the river, broad lowlands or depressions of the Inland Delta that are subject to inundation by 

normal or above-normal floods, and extensive dune tracts composed of stabilized and active dunes—Continued. 

(Approximate scale is 1:1,000,000.)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1058 51

EXPLANATION S-GB

Dunes and areas of other eolian deposit types can be identified 

easily on Landsat images from either false-color composites or 

black-and-white images, preferably of MSS bands 5 or 7. Interpretation of imagery, accompanied by onsite checking, 

could probably furnish enough information to aid in studies of 

the southward encroachment of the Sahara and desertification 

in the Sahel.

Stabilized longitudinal dunes trending east to east-northeast 

(solid-line contact). A reddish-brown soil is developed locally 

on these dunes.

Main areas of sand sheets or sand stripes (dashed-line contact).

Modern longitudinal dunes trending approximately northeast 

(dashed-line contact).

Erg (shifting sand); lines of the dune crests trend approximately 

north-northwest (dashed-line contact).

Area masked by clouds and shadows.
52 APPLICATION OF LANDSAT PRODUCTS, MALI, UPPER VOLTA, AND NIGER

References Cited

Archambault, Jean, 1960, Les eaux souterraines de 

PAfrique Occidentale: Service de I'Hydraulique de 

I'Afrique Oeste Francaise, Imprimerie BergerLevrault, Nerieg 137 p.

Comite Inter-Africain d'Etudes Hydrauliques (CIEH), 1972, 

(La culture du sorgho de decrue: L'utilisation 

agricole des eaux de crue en Afrique: Part 3), 

Society Generate des Techniques Hydro-Agricoles, 

Ougadougou, Upper Volta, 50 p.

Cooke, R. U., and Warren, Andrew, 1973, Geomorphology 

in deserts: University of California Press. Berkeley 

and Los Angeles, 374 p. plus index.

Church, R.J.H., 1968, West Africa: 6th ed., John Wiley 

& Sons, Inc., New York, 543 p.

———1973, The development of the water resources of 

the dry zone of West Africa, in Dalby, David, and 

Church, R. J. H., Drought in Africa, University of London, p. 62-66.

Dalby, David, and Church, R. J. H., eds., 1973, Drought in 

Africa: Centre for African Studies, University of London, 124 p.

Greigert, J., and Poygnet, R., 1965, Carte Geologique, 

Republique du Niger.

Grolier, M. J., Fary, R. W., Jr., and Gawarecki, S. J., 1974, 

The Sahelian zone remote sensing seminar and 

workshop at Bamako, Mali, West Africa, April 17-28, 

1973: U.S Geological Survey Open-File Report, p. 

74-196.

Grove, A. T., 1973, Desertification in the African

environment, in Dalby, David, and Church, R. J. H., 

Drought in Africa: University of London p. 33-45.

Grove, A. T., and Warren, Andrew, 1968, Quaternary 

landforms and climate on the south side of the 

Sahara: Geographical Journal, v. 135, June 1968, p. 

194-208.

Hopkins, Brian, 1965, Forest and savanna: Ibadan and 

London, Heinemann, 100 p.

Jones, J. R., and Miller, R. H., 1974, Application of ERTS 

technology in development programs for the 

Liptako-Gourma Authority countries (Mali, Niger, and 

Upper Volta): U.S. Geological Survey open-file report, 

16 p., 1 fig.

Keay, R.W.J., 1959, Vegetation map of Africa: Oxford 

University Press, London.

Marvier, L, 1952, Series hydrogeologiques de I'Afrique 

Occidentale (map), in Archambault, Jean, 1960, Les 

eaux souterraines de I'Afrique Occidentale: Service 

de I'Hydraulique I'Afrique Oeste Francaise, Nancy 

Imprimerie Berger-Levrault.

Morain, S. A., and Williams, D. L., 1973, Estimates of 

winter wheat yield from ERTS-1, in ERTS-1 Symposium, 3d, Washington, D.C., Dec. 1973: Proceedings, p. 21-28.

Reining, Priscilla, 1973, Utilization of ERTS-1 imagery in 

cultivation and settlement sites identification and 

carrying capacity estimates in Upper Volta and 

Niger: U.S. Agency for International Development, 

Contract Report No. AID/CM/AFR-c-73-21.

Sterling, Claire, 1974, The making of the Sub-saharan 

wasteland: The Atlantic, v. 233, no. 5, p. 98-105.

Tomiche, F. J., 1974, Man versus blackfly: World Health, 

May 1974, World Health Organization, Geneva, p. 

20-27.

Wade, Nicholas, 1974, Sahelian drought: No victory for 

western aid: Science, v. 185, p. 234-237.

Wigton, W. H., and Von Steen, D. H, 1973, Crop 

identification and acreage measurement utilizing 

ERTS imagery: 3d ERTS-1 Symposium, Dec. 10-14, 

Paper A5, Nat. Aeronaut. Space Agency, p. 87-92.