sweeting, marjorie m. the karstlands of jamaica

8/11/2019 Sweeting, Marjorie m. the Karstlands of Jamaica

1/18

THE KARSTLANDS

OF

JAMAICA

M.

M. SWEETING

THE ROUGH AND uneven surface of the country . renders it qulte impassab1ej

high peaks, steep hills, ravines, gullies, sink holes, etc. present

so

many

obstacles that this portion of the parish has well earned the appellation of 'terra

incognita'.

0

This is part of Sawkins' description in 1869 of the cockpit distriCIS

of Jamaica (pp. 195-6), some of the most striking areas of tropical karstt landscape

to be seen anywhere in the world. This paper describes the most important

characteristics of the Jamaican karstlands, particularly those in the north and centre

of the island, including the area known

as

the Cockpit Country.

Jamaica is essentially a mountainous and hilly island. Two-thirds of its area is

made

up

of highly dissected limestone plateaus, varying in height from

Iooo-JOOO

feet above sea level.

The

White Limestone Series upon which these karst

areas

have developed are Upper Eocene-Lower Miocene in age with a total thickness, n

places, of the order of 2000 feet. The general structure of central and western

Fig. Ia. Section across north

central

Jamaica after

Zans,

I95I

Jamaica is anticlinal, with an axial trend from ESE.-WNW.; in the core of this

anticline rocks older than the White Limestones are exposed. The White Lime

stones dip generally both to the north and to the south off the flanks of this Central

Inlier (Fig. 1a).

The

lithology of the White Limestones is variable. By

far

the greater part of the

Series consists of fairly coarse, crystalline, well-jointed and highly fissured lime

stones.

The

drainage in these pure and hard limestones

is

rapid, vertical and free;

.' vertical e r o s i o n - ~ is predominant.

Certain

of

the

White Limestone Series are,

however, of a semi-permeable, chalky or marly facies and contain abundant

flint

nodules; these beds are known

as

the Montpelier Beds and they occur in par

ticular along the northern coastal zone, where they are normally separated from the

crystalline facies by the Duanvale Fault Zone (Fig. 1 .1 The Montpelier Beds

form a semi-pervious stratum in which water circulation occurs only along the major

ee

list

of

references at the end.

t

The tenn "karst1and" has now passed into general use both in European and American

geographical writing. t is used to denote a region

of

massive limestone or dolomite where

the evolution of the relief is dependant upon chemical erosion, i.e. solution, as the dominant

proceiS in land form development and where, as

a result,

surface drainage becomes diverted

into underground channela. The word Karst is the German form

of

the Slovene word

Kras, meaning a bleak, waterless place and is the name given to the country inland {rom

Trieste.

The

Montpelier Beds are usually considered to represent an offshore facies

of

the

crystalline White Limeatones.:l


2/18

Black

River

Bay

Wolclestxm

;l t Somerset

~ j ~ t t i n o h o m

ile s

s r ~ w o r t own

DRY H RBOUR

/ J:icldy Pole

MOUNT INS

ut:l -flle f : . : ~ ; : : : : ~ PoftWhiu Umutofte

FoulcZon

White

lim stonft witlt

Montpelier

II IIIll Yellow LimatoM

===;

Pre Yellow LimutoM

flr rmont

Riwr ua

Fig. r Geological mop of north central Jamaica after llose nd V ersey, rgs6)


3/18

186

THE

KARSTLANDS

OF

JAMAICA

fault lines; erosion is horizontal rather than vertical, and lateral planation by

flood waters is usual. The basal beds of the White Limestones (the Troy Lime

stones) are sometimes dolomitized; such dolomites are cut by great joints which

influence considerably their weathering and erosion.l

The

upper beds

of

the Yellow Limestone,

of

mid-Eocene age, lie immediately

below the White Limestones and form the essential karst basis to the Jamaican

karst areas (Fig.

.

The Yellow Limestone consists of an upper and a lower lime

stone series, separated

by

a group of beds containing clays and tuffs; along the top

of

these beds and within the upper beds of the Yellow Limestone, there is a large

circulation of underground water. Well-developed karst features also occur within

the upper Yellow Limestones.

Both the White and Yellow Limestones were affected by the Antillean

move-

ments

of

mid-Miocene age; these movements produced some slight folding, but

more especially extensive block faulting. Many of the faults cutting the White

Limestone plateaus are of Miocene age. The main trend of these fault lines is E.-W,

and N.-S. with important sub-diagonal trends running

NNE.-SSW.

and

NNW.

SSE. Such lines of tectonic weakness are of fundamental importance in guiding the

directions of both surface erosion and the underground water flow.


4/18

. .

. .

Miles

Coekplt

\ o r ~ t

f'":""'":l

1. ..:.. .J

~ g r o d ~

Cnc lcpt Kor st

~ j j

Tower

Korst

De9raded Tower

l orst

Fig.

2

Karst land frmns JWTth tentral Jammca

0

P ~ y ~ l l o w l m ~ a t o n e

U lntt:riOf ' vollt') S Ot'

polj

Rocks mtWt' r

thc n

whiU llrttntoM'

D

Dolint'KOI ltt

N

t


5/18

188

THE

KARSTLANDS OF JAMAICA

Both these types occur in Jamaica, though their development is confined to the

areas of the hard crystalline White Limestone and to the areas of high rainfall.

In the areas where the White Limestone beds are more marly, or where the

rainfall is low, a doline karst develops with land forma resembling those found in

temperate latitudes.

oljes

(interior valleys) are normally associated with the

marly

limestones, since

polje

formation is closely connected with extensive flooding and

lateral planation.

The cockpit

karst

This type of karst landscape is the most widespread in Jamaica and is particularly

well developed in the north and centre (Figs. 2 and 3). Cockpit karst consists

essentially of a success;on of cone-like hills with alternating enclosed conical depres

sions or cockpits. A striking feature is the uniformity, both in area and in

height range,

of these depressions and the intervening hills. Thi s is clearly seen in

the sections (Figs. 3a and 3b), and in the photograph, plate

1 .

The

Cockpit Country proper in the parishes of Trelawny and St. James, forma a

region of continuous cockpit karst (Fig. 2). In this area the average depth of the

cockpits is between 300 feet and 400 feet, and some are as deep as 500 feet. A good

idea of their dimensions is given by the aneroid traverse across the area shown in

Figure 3; it will be seen that although the bases of some of the cockpits

may

be

about

4

mile across, there is little levelland in the true Cockpit Country. The bases

of the cockpits consist frequently of a puddled muddy area, containing yellow or

r o w n i s h ~ clay; in wet seasons, this area may contain a pond fomting a

small perched water-table. The slopes of the cockpits are usually between 30 to 40

and are made up of chemically weathered and honeycombed blocks and scree;

where the White Limestones are exposed, the sides are steeper and can be cliff-like.

Most of these slopes are covered with dense forest, though the bottoms of some of

the larger cockpits have been cleared for banana and yam cultivation.

The

cockpits and the cone-like hills are conspicuously arranged in lines following

the trend of the joint and fault patterns in the White Limestones, plate 1. This

rectilinear alignment has been .referred to by many workers in Tropical karst land

scapes and is often called gerkhteter ( directed ) karst. Individual cockpits are

extended by growth along lines of jointing and faulting, and two or more may

coalesce and enlarge along a well-defined tectonic line. This has happened at

Barbecue Bottom, a depression more than mile long and 400 feet deep, and

situated along a

N N E . ~ S S W . t r e n d i n g

fault line in the north-east part of the

Cockpit Country. Such elongated and enlarged cockpita are called glades and

are the equivalent of uvalas.l

Nonnally the cockpita and conical hills are more or less symmetrical, but some

times the slopes on one side of a cockpit are steeper than those on the other. This

asymmetry seems to occur

as

a

result

of two circumstances First

n areas

where

the dip of the White Limestones becomes greater than a few degrees, the slopes of

the cockpita are more gentle along the dip slopes and steeper on the

up-dip

side;

this is illustrated in the south-west part of the Cockpit Country near Retirement.

Secondly, asymmetry is common in cockpit karst near the north coast, where the

slopes are steeper on the south and south-west sides and less steep on the north

side; this suggesta that in this part of Jamaica, at least, solution and weathering of

the limestones is greater on the northern slopes which face the incoming trade

winds

1

So

c.alled for their resemblance to the arenas for cockfighting.


6/18

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t

'

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0

'

;

CO'UNTRY

/ :

\

DRY HARBOUR

: p

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,' \ /

- . /J ' I \ XA.Ift'....,..,. _...;, & '

---.._AH.,.. ~

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\MOUNTA INS .,. '

MQNCAGUC , /

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\

' \ ' - ~ '

~ d o .

I - I A

- - . . - -

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~ - . . . . - , ~ - - - . . . ~ j

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OISTRICT

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.

\ > ' - \ ~

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\ lll 1 1

\tl

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' .. - \ ', ,

\ ~ t + ' _ ,

X

~ c ; . , . . \ '

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\ ,_ ___________ -------? ) \. >

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. . . _

I / / ST.TH.j _

-

Mttj- .,.," P

e ltlue holft

0

Mojor

3WOtfow holu (slnb}

a

Mojor cow

__ .Proboth UnH of

undcr - d -ur-n

- -

Moin tenhed of'

lslond

_A ,Kim4PU liM

af

. . . . .o;d

~ { H e f i ~ .

JbJ

~ ~ ~ ~ -

10

Fig. J.

Main

features of

the hydrology

north central

Jamaica


7/18

'90

THB KARSTLANDS

OF

JAMAICA

In the Cockpit Country the summits of the conical hills tend to reach to an even

summit-level at a height which varies from

1000

feet to

2000

feet; this summit

level is in part a structural surface, but may also be part of a more extensive pene

plain (Figs. 3a and 3b).s

The

skyline of this summit surface shows two types of

dissection-a shallow dissection up to so-70 feet by cockpits which may be regarded

as one-cycle land forms, and a deeper dissection by the larger and more successful

cockpits, which may be multicycle land forms (Figs. 3a and 3b).

True cockpit karst occurs only in areas where the hard crystalline White Lime

stones outcrop.

In

these areas rainwater sinks immediately into fissures in the rock

and it is doubtful if normal fluvial erosion has ever taken place. Rivers rising on the

more impermeable and less fissured beds below the White Limestones sink into

holes very shortly after crossing on to the crystalline White Limestones. This is

well seen along the south-eastern side of the Cockpit Country, where every river

flowing off the rocks of the Central Inlier ends in a blind valley. Some of the

rivers sink into a series of muddy and stony holes in the line of the river's bed, as in

the Hector's river; more frequently, the rivers disappear into a slightly inclined

bedding-plane cave, as in the One Eye River at Wallingford Sink (Fig. 3). The

blind \'alleys are often terminated on the downstream side by limestone cliffs, vary

ing in height from 5o-2oo feet.

water-table in the accepted sense

is

not present in the crystalline White

Limestone areas, though a rest-level of variable height may be recognized. Deepen

ing and enlargement of cockpits takes place by solution caused by acidulated

\Vater

from the dense vegetation and from temporary ponded water, acting along the lines

of fissure. The nature of the cockpit karst changes when the bases of the cockpits

extend down to a level where they are frequently flooded.

In

normal cockpit karst,

the

subterranean circulation of water in conduits and caves is well below the base

of the deepest cockpits.S

It

is of interest to record the Geological Survey's original explanation of the for

mation of the cockpit depressions. Sawkins wrote in 186g, The waters sinking

through the cavernous structure of

the

limestones, forced their way through and

removed the subjacent beds of shale and sand, thus forming cavities below the

limestone which being unsupported gave way and originated the 'Cockpit' depres

sions (p. 24 2

1

. a n e ~

was

the first worker to adopt the hypothesis that these

depressions originated predominantly by solution of the limestones along joints and

fissures; he assumed that local collapse of caverns would also help to enlarge the

hoUows. Modern workhas taken the solution ideas f Dane for granted; how

ever, it should be noted that Meyerhoff writing in 1933 of the Sumideros (similar

land forms to cockpits) of the Lares area in Puerto

Rico

regarded these depressions

as being almost entirely unroofed caverns. From the regular distribution and

linear arrangement of the cockpits in Jamaica and their dissociation from the sub

terranean circulation of water, it would seem that they are formed largely by

solution and subsequent enlargement by collapse along fissures; it is difficult to

believe that such a regular pattern would be brought about entirely by collapse of

cavern roofs, unless such collapse was very systematic.

0

lu tower k rst

Tower (or Turm karst, like the cockpit karat, occurs only on the crystalline

White Limestones but s much less widespread; its distribution is shown in

Local

co iapse of cavern roofs is of course important, one of

the best examplea being

Dunn s Hole, 1 cliff-bounded chasm over 400 deep, south

of

Stewart Town,


8/18

w.

u' -,.s,n S' r_,.

1 r

/ .

1000

10;?0

O 0 2 3 4 6 7

I

8 I )

II 12 1)

M 1G

l ' f tl

IJI 20

:1 01

O

-

OO(I

fOliO

s

ln.g/od.

tolll t t

L

' ~ ' '

l

F1g.3o. Section west

to

east:

across

t:he

Cockpit

Country

Based on

D.O.$.

map

r

Jamaica, on

t:so,ooo

Bounth 'Y ktwt t:,.

L1mds

St>ldit:> lt

Lond

Bf'(XI(/It:of'

MNI'tt:l

r id$lt

l ,NdJ

c,., l .

s.. Jl

' 'f '

s TJ

Boundary betwtmrr

lewJs

I I D b i , . , ~ . , ;

Ptro nt

:

P


9/18

THE KARSTLANDS OF JAMAICA

Figure

2.

Tower

karst

is made up of steeppsided, forest-covered hills

or

mogotes

whose slopes vary between 6o

and go

Each hill or group of hills is separated

by a more or less flat alluvial plain which is often inundated. he height of the hills

above the plain is usually about

3 feet,

but may be

as

much

as

soo feet. The

bases of the hills are frequently the sites of springs and are honeycombed with

caves (Fig. 3 .

Tower karst develops where the bases of the cockpits extend

to

the underlying

rest-level of the water, when solution and sapping along the base and sides of the

cockpit takes place. Hence, geological and physiographical circumstances which

tend to produce a water-table or a spring-line

are

favourable for the development

of

tower

karst.

Erosion, particularly corrosion, by springs and flood waters

at the

base

of

the cockpits gives rise to the steeper, sometimes overhanging, sides, and

also to the flatter alluvial floors, both of which are characteristic of tower karst.

he slipping of the limestone blocks along joint-planes assists the widening of the

base of the cockpits and

also

the parallel retreat of the steep-sided hill-slopes. Each

successive flooding of the floor of the cockpit adds further

to

the deposit of alluvium.

The

development

of

tower

karst

is usually associated with large-scale lateral move

ments of water and explains why the bases of these steep-sided hills are the sites of

both large springs and caves.

Conditions favouring the development of large springs and lateral planation by

flood waters occur near and at the base

of

the \Vhite Limestones at their junction

with the Yellow Limestone and also

in

those areas where the crystalline facies of

the \Vhite Limestone

are

in close association with the marly vlontpelier facies.

Tower

karst formation at the base of the \'llhite Limestones is well illustrated in the

Maroon Town

area

along the east

and

west sides

of

the Cockpit Country, where

steep tower-like masses of the White Limestone (plates

2

and 3 rest upon a

stripped surface of Yellow Limestone. Further, in those areas, as in the Cave River

Valley, where the basal beds of the White Limestone are dolomitized, the strongly

marked vertical jointing characteristic

of

those beds is

an

important factor in tower

karst

development. Tower karst also occurs

in

the neighbourhood of the Duanvale

Faul t Zone, along the northern margin of the Cockpit Country. Here the crystal

line hite Limestones give way to the l\1ontpelier Beds; the semi-permeable

and tightly-jointed nature

of

the l\1ontpelier Beds encourages a more horizontal

or lateral circulation

of

underground water with the formation

of

large springs.

Relatively rapid spring-head recession is frequently associated with tower karst

particularly when. the springs are cutting back along a fault-line,

as at

Windsor

(Fig. 3). Such recession

gives

rise to flat-floored, steep-sided and steep-headed

pocket valleys" which

are

a normal accompaniment to tower karst development;

the northern margin of the Cockpit Country is much indented with pocket

valleys."

A slackening of the karst (solutional) processes can cause both cockpit and

tower

karst

to become degraded, In degraded cockpit karst, effective deepening of

the cockpitsceases, the sides slump

in

and

the slopes become more gentle, about

20

to

30 The

cockpits

are

consequently shallower, and the relief becomes more

subdued and rolling. There is also

an

even greater dissociation between the surface

water

in

the cockpits and the ground water circulation

at

depth. Considerable

areas

of

degraded karst occur

in

northern and central Jamaica, particularly

in

the Dry

Harbour Mountains where it is associated with large deposits of bauxite (Fig. 2 .

sweeting, marjorie m. the karstlands of jamaica

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