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III. The Environment of Laterite

III. The Environment of Laterite

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conflicting views may be the result of two confounding factors: (1) the

occurrence of laterite under climates that are unlike those under which

the laterite formed, and ( 2 ) differential effectiveness of climatic wetness

or dryness in combination with differences of topography, parent material, and time.

Laterite is found where temperatures are warm or are believed to

have been warm at the time of formation. This does not preclude the

possibility, however, that time, not temperature, is the controlling

factor. If the principal effect of high temperature is to accelerate rates of

reactions, the time interval necessary for laterite formation in temperate

regions may exceed the period of time that appropriate landscapes have

been stable. Similarly, observations of Oldham ( 1893), Joachim and Kandiah (1935), and Prescott and Pendleton (1952) that laterite has not

formed under the cool temperatures of highlands in the tropics may be

due less to cool temperature than to landscape instability. Nevertheless,

field observation generally agree with the hypothesis that warm temperatures favor the formation of laterite.


A forest vegetation was considered necessary for laterite formation by

Glinka (1927, pp. 33-34). More detailed observations have shown that,

while laterite occurs in regions with a rain-forest vegetation, welldeveloped laterite is most commonly found under a low forest and that

hard surficial laterite is a very common feature of the open savannah

adjacent to the forest. Maignien (1958, p. 16) concluded that laterite is

most extensive and strongly expressed at the boundary of forest and

savannah. DHoore (1954,1957, p. 55) found iron mobilized to a greater

degree and to greater depth under tropical grasses than under forest.

Buchanan’s type of soft laterite is found in Ceylon in the forested areas

of the southwestern lowland.

Humbert (1948) suggested that laterite forms in a climate that has a

wet and a dry season, and his descriptions and illustrations indicate that

the laterite he observed was in an open savannah that was gradually

replacing forest, a common condition where a dry season is prominent.

The change from soft laterite to the hard form within a few years after

man has cleared the forests has been reported by Alexander and Cady

( 1962) in French Guinea and other parts of West Africa. Blackie’s (1949)

description of soils of Fiji and Aubert’s (1950) description of Dahomey

also confirm the hardening of laterite following a change from forest to

savannah caused by man’s activities. It would appear from the literature

that laterite is most extensive in areas of savannah but that laterite forms

under forest though its hardening is favored by lack of forest cover.



Nodular forms are very common in forested areas, though they also

appear to be most widespread in the savannah.

Rosevear ( 1942) has reported a case where reforestation softened

hard laterite significantly in as little as 16 years. The possible explanations

of the effect of vegetation on hardening and softening will be considered




Laterite is found overlying a variety of kinds of rock. It is common

over basic igneous rocks such as basalt, norite, and diabase as well as

over acid rocks such as granite, granulites, gneisses, and sericitic schists.

Laterite has also been observed on shale, sandstone, and other sedimentary rocks including limestone (Jones, 1943; Stephens, 1946, p. 11).

Marbut (1932, p. 76) has described laterite outcropping on the banks of

the Amazon, presumably in alluvium, in association with a ground water

table. Maignien (1958) has shown that fermginous laterites may develop

on a variety of materials providing there i s a source of iron either in

the parent rock or in adjacent higher-lying areas from which water may

introduce ferruginous material.

The laterite layers may be in material unrelated to the underlying

bedrock. In some places, laterite clearly has formed in residuum of

rocks that have weathered in place, as evidenced by features such as a

constant proportion of iron oxides to alumina with depth or by a

continuation of quartz veins from the rock into the laterite. It is also

found in colluvial deposits; examples are described by Maignien ( 1958).

Often laterite is associated with material that has been transported

locally; recently recognition of stone lines in surhial mantles of this

character has directed attention to the frequency of such conditions

(Ruhe, 1959). Though such surficial deposits may not be directly

related to the underlying bedrock, they may not be very different from

residuum of the major rocks in the locality, since transport is often of a

local nature as in cases cited by Nye (1955a) and by Ollier ( 1959). The

parent material in which laterite forms may also be derived from material

of different and highly contrasting strata than the underlying rock

currently present. Whatever the source of material in which laterite

forms, an adequate supply of iron appears to be essential. Alexander and

Cady (1962) have noted that the thickness of laterite crusts is sometimes

related to the iron-richness of associated rocks.


Laterite has been generally associated with a level or gently sloping

surface. This characteristic was emphasized by Oldham (1893) in his

review of numerous laterite locations in India and has been subsequently



confirmed by many workers from other parts of the tropics. Campbell

( 1917), from his many observations, reported that laterite currently

being formed covers the flatter ground and stops where the slopes are

steep. Holmes (1914) observed that in Mozambique laterite occurs only

on gently undulating plateaus and never on steep slopes. Humbert

(1948), from his study of laterite in Australian New Guinea, concluded

that the best examples of laterite occur almost exclusively on areas of

low relief and gentle slopes. Prescott and Pendleton (1952, pp. 25-26)

also emphasized the nearly level nature of the terrain where laterite


The horizontal disposition of laterite deposits is very striking in many

relatively arid regions. Newbold (1846) observed that in the interior of

South India laterite occurs in almost horizontal beds as cappings on the

tops of mountains. Woolnough (1918) emphasized the significance of

relic laterite deposits in western Australia on slightly elevated plateaus.

Similarly in southwestern Australia, laterite is found in many localities as

massive or concretionary deposits forming protective cappings on flattopped residuals (Mulcahy, 1960, 1962). Laterite is also present in

extensive bodies on dissected tablelands (Stephens, 1946).

Laterite is found along river banks and on terraces adjacent to higher

ground. These masses of “gallery laterite” are believed by DHoore (1957,

p. 97) to be formed by enrichment with iron during flood stage followed

by its immobilization when the flood subsides. In the flat humid areas,

where it is believed that laterite is forming currently, a high but

fluctuating water table is common. The drainage is more or less imperfect,

and the ground water at and below the water table is thought to be

somewhat sluggish. This has led to a common opinion that topography

conducive to a high water table may be essential.

Soft laterite is found at a shallow depth on low hillocks in southwestern Ceylon, generally not much more than 100 to 200 feet above sea

level (Prescott and Pendleton, 1952, p. 9 ) . The slopes are undulating and

are certainly not level, Though Oldham (1893) dismissed these occurrences as “a more or less ferruginous subsoil which never passes into

laterite,” the descriptions of Joachin and Kandiah (1935) indicate that

these materials, locally called “cabook,” conform to Buchanan’s concept

in every way. It should be noted, however, that the underlying rock in

this region is charnockite, a quartzo-feldspathic gneiss or granulite with

hypersthene, and that the rainfall is over 100 inches per annum but with

dry intervals. High rainfall and high iron content of the parent rock

may favor the formation of laterite even where the surface is not level

but is stable owing to the nature of the weathered material and forest

cover. Mulcahy (1960, p. 222, 1962) emphasized that peneplain condi-



tions of low relief are not essential, though low available relief conducive

to stable land surfaces for long periods is most favorable.

Laterite on areas of low relief, nevertheless, is the most common.

Blanford (1879) classified the Indian laterites into high-level and lowlevel varieties, depending on the mode of occurrence. This distinction

was at first intended only to signify two contrasting positions, high-level

laterite capping the summits of hills and plateaus on the highlands of

central and western India and low-level laterite covering large tracts in

the coastal regions (Holland, 1903).

Subsequent workers observed that low-level laterite is generally

the more fenvginous and commonly does not exceed 30 feet in thickness.

It also commonly contains inclusions of sand and pebbles, which indicate

a multicycle or detrital origin (Oldham, 1893). Low-level laterite, however, does not everywhere contain such foreign inclusions. Since it was

once thought that laterite can form only at or near the water table, the

low-level laterite on areas with a high water table was called “live”

laterite. The laterite on ground above the reach of the water table was

thought to have been a product of an earlier period when the groundwater fluctuation reached the laterite zone. Hence, this was called “dead

laterite ( Campbell, 1917).

The high-level laterite is generally more homogeneous and may be

relatively thick, as much as 100 to 200 feet according to Oldham (1893),

though it is probable that such thickness is a feature of plateau margins.

Though it was considered “dead” by Campbell ( 1917), Harrison (1933,

p. 16) believed that laterite can form on high-level positions, as on the

plateau of the Eagle Mountain range in British Guiana, under conditions

of heavy rainfall though the water table is low. As it is presumably being

formed currently, this would be called “live” laterite. Laterite in highlevel position may include pebbles from even higher surfaces, indicating

detrital origin (Ruhe, 1954, p. 18).

The laterite found on distinct slopes adjacent to higher ground may

be called foot-slope laterite to indicate its topography. It is often detrital,

being formed by the consolidation of fragments of the laterite of the

higher level that have moved down the slope as erosion has advanced

(Oldham, 1893). The second member of Greene’s ( 1945) “ironstone

catena” would be this class. “Terrace” laterite occurs on terraces adjacent

to high ground or along the banks of streams. It is thought to be formed

by the deposition of dissolved material where ground water moving

laterally and down the adjacent slope encounters the oxidizing conditions

of the surface horizons (Campbell, 1917). Maignien (1958, 1959) emphasized the occurrence of laterite crusts at the borders of natural

drainage areas, such as piedmonts, river banks, dissection forms, and



other abrupt breaks in slopes where the profile of a saturated zone

approaches the surface. Another type recognized by Fermor (1911) is

“lake” laterite formed in marshy areas by water flowing from the

surrounding higher land, either along the surface or by seepage.

Lake (1890) used the accompanying tabulation to classify the laterites

in Malabar, India, according to topographic position, character, and origin:


Nature of the laterite


Plateau laterite

Terrace laterite

Valley laterite



Partly vesicular

Partly pellety



Partly nondetrital

Partly detrital

More elaborate schemes of classification, based on other factors, have

been published by DHoore (1955),Maignien (1958), and du Preez


Four physiographically distinct landscapes with which laterite is

commonly identified in the literature are: (1) high-level peneplain

remnants, (2) colluvial footslopes subject to water seepage, ( 3 ) lowlevel plains having high water tables or receiving water from higher

land, (4) residual uplands other than peneplain remnants. The first

three are illustrated diagramatically in Fig. 1.

Hlgh-Level Plateou

wlth Loterite Cap

Laterits Detritus

Laterite Enriched

FIG. 1. Relationships among physiographically distinct landscapes with which

laterite is commonly associated.

Laterite on high-level peneplain remnants may be in residuum of

rocks weathered in place or may be in transported material deposited

prior to peneplain dissection. Its present position is a consequence of

landscape inversion such as that described by Bonnault (1938); it once

occupied a low-level position comparable to that illustrated in Fig. 1.

With uplift or with lowering of base level, areas protected by laterite

have remained as erosion lowered the surrounding areas. Such areas

now occupy the highest positions and are being reduced slowly by




lateral retreat of slopes, as on the two Tertiary surfaces described by

Ruhe (1954, p. 18-25).

At the base of peneplain remnants, detritus from above, including

fragments of the crust, accumulates and is recemented to form younger

laterite on the colluvial footslope (Maignien, 1958, 1959; D’Hoore, 1954,

1957). On low-level plains soft laterite is commonly currently forming

above a water table; and on undulating upland surfaces, laterite may be

forming locally in clayey iron-rich residuum whose impervious nature

periodically causes saturation with water.


Many existing laterites are clearly relics of geologic antiquity. Those

of Queensland, Australia, are reported to be products of two humid

periods of the Pliocene (Whitehouse, 1940). In Ceylon, of the crusts

described most are thought to be products of the Pleistocene and some,

of Pliocene or earlier periods (Fernando, 1948). Laterites of Nioka

(Ituri), Congo have been related to mid- and late-tertiary surfaces by

Ruhe (1954). Though laterite may be forming currently on some ancient

peneplain remnants, many high-level crusts are considered to be “dead

products of the age of peneplain development. Their existence may

commonly be considered a factor in the preservation of the land forms

on which they occur, and the period since the lowering of base level is

a measure of the time required for landscape inversion under given


Nevertheless, many examples of laterite believed to be forming

currently have been reported ( Fermor, 1911; Simpson, 1912; Campbell,

1917; Marbut, 1932; Harrison, 1933; Joachim and Kandiah, 1941; Pendleton and Sharasuvana, 1942; Kellogg and Davol, 1949). Though it is

commonly assumed that formation of laterite requires a very long time,

some laterites of “absolute accumulation” ( D’Hoore, 1957, pp. 94-98)

apparently may form rapidly. Obviously, formation of laterite from solid

unweathered rock can be no more rapid than the time required to attain

a high degree of weathering. In unconsolidated weathered material

subject to enrichment in iron from outside sources, however, rate of

development may be relatively rapid. Hardening of the soft preconditioned material may take place in a few years upon exposure

(Alexander and Cady, 1962).

IV. Profiles Containing Laterite

Though either nodular or vesicular laterite may lie within, and may

be genetically related to, the solum of the modem soil, as defined by

the Soil Survey Staff of U.S.D.A. (1951), many laterites appear to be



unrelated genetically to present soil horizons. Consequently, the Soil

Survey Staff (1960) has defined “plinthite” independently of soil horizon

definitions, though they use the presence of soft “plinthite” within the

solum as a criterion of soil classification. This discussion is concerned

with horizons or layers in the entire weathered section, which commonly

is much thicker than the part that would be considered “solum.”



At sites where laterite is thought to be forming, it is generally found

as a shallow but not surficial layer. Prescott and Pendleton (1952)

reported laterite in Ceylon at various depths, averaging about 2 feet, and

in Thailand from a fraction of a foot to 6 feet. Humbert (1948) described

“red to yellow loam” 2 to 6 feet thick over laterite in Queensland. Some

Iaterite layers have been described by Alexander and Cady (1!362) at a

depth as great as 13 feet in Sierra Leone but others were found near or

at the surface. Similar observations are very numerous in the literature

and indicate that soil material over laterite is mainly less than 10 feet

thick. Laterite crusts at the surface are very widespread ( Oldham, 1893;

Maclaren, 1906; Simpson, 1912; Walther, 1915; Prescott and Pendleton,

1952, among many authors), but such exposure is generally attributed to

erosion. Though hardening of laterite is thought to be a phenomenon

favored by surface position, the literature implies that the initial

development of material that will harden most commonly occurs at

some depth below the surface. Hardened laterite crusts as thick as 200

feet (Oldham, 1893) suggest that development can proceed to this

depth, but such an extreme may be only at the edge of peneplain remnants where the material is affected by vertical exposure. A crust 30 feet

thick has been reported by Alexander and Cady (1962); Campbell

(1917) observed that laterite seldom exceeds 30 feet in thickness.

Mohr (1944) considered laterite to be essentially a soil horizon of

sesquioxide accumulation to which the overlying soil material is related

genetically. This concept has been elaborated by Mohr and van Baren

(1954, pp. 300304) and was accepted by Pendleton (1936, p. 106).

Marbut ( 1932) postulated a comparable genetic relationship between

laterite and soil material above it. In all these cases, the authors have

dealt with restricted conditions, comparable in many respects to the

original laterite of Buchanan. The work of Maignien (1958, 1959),

Mulcahy (1960), and D’Hoore (1954, 1957) and observations by the

authors (Alexander and Cady, 1962) show clearly that the presence of

a suficial mantle of soil over laterite is no assurance that the soil is

related to the underlying laterite genetically, or that if genetic relationships are involved, they may be quite unlike those postulated.




The overlying soil material may be from sources different than the

material in which the laterite has formed. Stone lines marking erosion

surfaces (Ruhe, 19.59) are very common in the tropics and may mark

major discontinuities of material vertically. Ollier ( 1959), however, has

reported extensive areas in Uganda where the stone lines appear to be

the result of sorting by termites, leaving coarse fragments below and

moving fine earth to the surface. Nye (1954) also emphasized the

activities of termites but reported substantial sorting and downslope

creep of the sorted material. Berry and Ruxton (1959) also have

emphasized an upper zone of migration. Resistant minerals, such as

quartz, in soil over laterite from quartz-free rock are common and

indicate at least contamination of the upper layers of material from

outside sources.

In some cases surface material can be demonstrated to be residual

from the same rock as that from which underlying laterite has formed

and either predates or is contemporaneous with the laterite. There are

also cases known to the authors in which a surficial soil mantle has

developed by disintegration of the upper part of a laterite crust. Such

soils are commonly thin over the laterite and contain pieces of the

disintegrating laterite.

Thus, a great variety of soils may overlie laterite. Where such soil

horizons are residual, they are composed of highly weathered material

high in sesquioxides with or without kaolin and with some component of

whatever highly resistant minerals may have been present in the parent

rock. They may be uniform in character with depth, like Latosols, or

may have genetic A-B horizon sequences not unlike Red-Yellow Podzolic

Soils. Commonly, the first laterite encountered with depth is in the form

of individual nodules within the soil horizons. These may reach a

maximum with depth below which they decrease without being joined

into masses as in examples given by Nye (1954, 1955a) and Radwanski

and Ollier (1959), or they may pass into masses of nodular or vesicular

laterite, as in profiles described by Joachim and Kandiah (1941) and

Ollier (1959).

B. LA-


Many soils of the tropics have laterite within genetic horizons. These

may be detrital nodules or fragments from adjacent higher-lying landscapes containing laterite ( Greene, 1945; Ruhe, 1954), relics of disintegrating laterite crusts in which soils are forming (Mulcahy, 1960, 1962),

or units developing concurrently with the modem soil (Ollier, 1959).

The “murram” used for surfacing roads in India (Prescott and Pendleton,

1952) is mainly nodular laterite and may be in horizons of the modern




soil. The authors have observed profiles comparable to both Red-Yellow

Podzolic Soils and Latosols, both containing nodular laterite in various

horizons, in widely separated areas of East and West Africa and in the

Philippines. The Tifton series, a Red-Yellow Podzolic Soil of southeastern United States, contains laterite nodules in both Az and B horizons.

The nodules in the B horizon of Tifton are intact and either forming or

stable, whereas those in the A2 are apparently dissolving, leaving quartz

grains protruding from the iron-rich matrix. Similar conditions in soils







Horizontal Scole, Feet






.z 3 6 -






Dork. Sendy Loom

h r k . Sandy Loom

Red Sandy

Red So*


with M Nodule.


84 -







Red Sandy

Cloy with

Few Fins



Dork.Sandy Loom

Groyirh Brown

Cloy Loom

rnth Commn




Mottled Sandy

cloy Loam




Mottled Red

I and Brownish

Yellow Sandy

Clov Loom





0ork.Sondy Loom

GIOY Sandy

Clay with

Few Matller

FIG.2. Laterite nodules in soils of a catenary association of Southern Nigeria.

containing iron nodules have been observed in Southern Rhodesia and

parts of Australia by the authors.

Though laterite nodules are common in soils that have no obvious

high water table ( Raychaudhuri, 1941) , such nodules commonly increase

progressively downslope on a given land form. Figure 2 shows this

relationship at a site near Ibadan, Xigeria where proximity of a zone of

saturation to the surface appears to be a controlling factor. It is believed

that these are developing concurrently with the modem soil and are

analogous to the forms described by Nye (1954, 1955a) in Ghana.

In the “Ground-Water Laterite” soil described by Kellogg and Davol



(1949), the laterite is considered to be a genetic horizon of the modern

soil. In this profile, laterite nodules are present at a depth of 8 inches,

increase in numbers with depth, and occupy a major part of a weakly

cemented horizon from 23 to 45 inches, which rests on soft massive

laterite that hardens upon exposure to air. Mohr (1944) and Mohr and

van Baren ( 1954) have postulated progressive soil development involving

( I ) laterite-free profiles in which an impervious substratum forms, ( 2 )

stages having horizons containing nodular laterite, and ( 3 ) a final stage

involving massive laterite.

C. Homoss




Obviously, detrital laterite fragments and nodules come to rest

capriciously on whatever material may be present on footslopes of

dissection forms, and in such areas of landscape inversion (Bonnault,

1938) the detrital laterite and the underlying material may be unrelated.

The laterite detritus, however, commonly contributes iron to enrichment

of adjacent layers (Maignien, 1958, 1959). A great variety of unrelated

layers may be found under laterite zones in such positions.

Where the laterite zone is apparently residual, however, the literature

reveals some measure of consistency of kinds of underlying layers.

Though Holland (1903) reported that laterite may rest on unaltered

bedrock, most descriptions show highly weathered, commonly thick,

earthy layers between the laterite zone and bedrock. In dry areas or

where conditions contribute to good aeration, as on some high-level

positions, the underlying material may be high in chroma (bright

colored) though commonly variegated in color ( Kellogg and Davol,

1949, p. 52). More commonly, especially on low-level positions, the

laterite zone is underlain by either a mottled zone, a light-colored layer,

or both, suggestive of poor aeration, reduction of iron, and possible

lateral leaching of sesquioxides.

U‘alther ( 1915) introduced the terms “mottled zone” and “pallid zone”

for comparable parts of profiles of western Australia, which contained

the following layers: (1) ironstone crust, ( 2 ) mottled zone, ( 3 ) pallid

zone, and (4)parent rock.

Simpson (1912) described similar sequences on both granite and

greenstone schist in the same region. Though Maclaren (1906) used

different terms in describing a lSfoot section in India, his sequence,

hard laterite-soft laterite-reddish buff sandy clay-white

grit-decomposed biotite and quartz schist, is very similar. Marbut’s (1932, p. 74)

idealized description of typical “Ground-Water Laterite” of the Amazon

Valley and Cuba reveals the same layers: (1) soil, ( 2 ) iron-oxide layer,



porous, slaglike, (3) mottled layer, ( 4 ) gray layer, and (5) unconsolidated clay and sand. He reported that the gray layer (pallid zone) may

be absent. Kellogg and Davol (1949) did not specify distinct mottled

and pallid zones in a “Ground-Water Laterite” of the Congo, but their

description shows mottling intermingled with high color values ( light

colors) in the lower part of the profile. Mohr and van Baren ( 1954,

p. 302) described similar layers in idealized profiles on volcanic ash

in which laterite is formidg in Indonesia:

- Redearth

B3- Layer of mottled




clay differentiable into an upper layer

of Fe203(incipient laterite) and a lower gibbsitic layer

(mottled zone?)

Spotted white clay (pallid zone)

Layer with siliceous cement

Unaltered ash of the basic suite

The numbering of “ B horizons by superscripts upward indicates the

hypothesis of development upward above the slowly permeable silicacemented B1 layer, which supports a perched water table.

Mulcahy (1960, 1962) described thick pallid zones in Australia under

ancient laterite in high-level positions where mean annual rainfall is

now less than 20 inches per year, their thickness decreasing from 60 or

80 feet under 20 inches of rain to about 10 feet under 13 inches. Jessop

(1960) described pallid zones from 60 to 200 feet thick in the southeastern part of the Australian arid zone under a silicified cap on plateau

remnants and concluded that the pallid zone is a relic of an ancient

profile from which the ferruginous material has been stripped. From

observations in Africa and Australia, Alexander has concluded that some

pallid zones are consequences of exclusion of air by overlying laterite;

they appear to be actively forming even on high-level positions in

relatively dry climates when they lie beneath a crust dense enough to

permit little access of air and where the zone is saturated for some period

during a rainy season. A profile by Kellogg and Davol (1949, p. 52) in

the Congo suggests that on relatively dry sites a thick (4-foot) layer of

unmottled soil, comparable to laterite-free soils of the locality, may

lie between a relic laterite crust and a mottled zone.

Commonly immediately above unweathered rock is a soft layer that

has undergone major chemical change while retaining the structural

character of the rock from which it was formed. This was called “zersatz”

by Harrassowitz (1926, 1930). This may lie beneath a mottled or pallid

zone, as in the “Ground-Water Laterite” of Kellogg and Davol (1949).

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III. The Environment of Laterite

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