INDIAN JOURNAL OF GEOMORPHOLOGY

Volume 8 Number 1&2, 2003, pp.35-42

COASTAL MORPHOLOGY OF KERALA FROM VIZHINJAM TO KOCHI

NARAYANAN, V.1 and ANIRUDHAN, S.2

Department of Geology, University of Kerala, Kariavattom, Thiruvananthapuram

695 581. 1nara22in@yahoo.co.uk & 2sap5354@rediffmail.com

ABSTRACT

The coast of Kerala from Vizhinjam to Kochi has been studied to describe

morphological variants in relation to tectonics and sedimentation. Delineation of various

features was done by examining aerial photographs of scale 1: 16000 and cross-checked with

the Survey of India Topo sheet followed by ground truth checking in selected areas to finalize

the geomorphology. Generally, fabulous beaches, lagoons, and sandbars compose the coastal

stretch. A schematic of shelf topography from off Vizhinjam to Ponnani is conspicuous by the

presence of seaward promontory called Alleppey platform, which divides the continental shelf

into two geomorphic units to its north and south. The southern shelf (S of Kollam) has a

concave off shore profile with steep shelf edge and the coastline in this part shows evidences

of upliftment (wave cut platform/ marine terraces). The northern shelf is wide with gentle

shelf edge and wide beaches, lagoons, strandlines and mudflats occupy the coastline here.

The evolution of coastal features is connected with the sea level rise during Holocene and the

lineaments cutting across the coastal land up to the shelf edge especially the one trending,

ENE - WSW.

Introduction

Kerala has a long coastal stretch of ~ 560 km. Geomorphology and evolution of

Kerala coast with special emphasis on neotectonism has been given by number of workers

(Thrivikramaji, et al, 1983; Nair, 1987, 1990; Nair, 1989, 1996, 2003; Soman 2002 and

Soman et al, 2002). Varadarajan & Nair (1978) identified at least four sets of lineaments

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cutting across the Precambrian terrain of Kerala and attributed that NNW - SSE and N

S.

lineaments are responsible for shaping the present coastline whereas NW - SE to WNW - ESE

(Achankovil shear zone) lineament controls the Tertiary Sedimentary basin. According to

them, Vembanad Lake probably originated in an embankment, which was controlled by a set

of graben faults. Lineaments of NE - SW to ENE - WSW direction are considered as

neotectonically active affecting the Quaternary sediments (Nair, 1996). Raha et al, (1983) and

Rajendran et al, (1989) proposed that the geomorphic features of Kerala coast are shaped by

Holocene transgression. Prabhakar Rao et al, (1985) identified lineaments of varying trends

viz., NW - SE, NNW - SSE, ENE - WSW and WNW - ESE. Of these, ENE - WSW trending

lineament extends into the coastal sedimentaries and beyond into the offshore region of

Kerala.

Prominent coastal geomorphic features of Kerala coast are beaches, beach cliffs,

stacks, shore-platforms, spits and bars, beach ridges, estuaries and lagoons, mudflats and tidal

flats and delta (Nair, 1999). Thrivikramaji et al, (1983) divided the Kerala's shoreline as

permeable gently sloping sandy shoreline, semi - permeable cliffed sedimentary shoreline and

impermeable, crystalline shoreline.

Suchindan, et al, (1987) divided the shoreline of Kerala as strand plain shoreline,

cliffed shoreline without a beach and cliffed shoreline with a beach. . Nair (1989, 1996 and

2003) proposed a morphostratigraphic unit for the coastal plain as Kunnamkulam surface,

Guruvayur surface, Ponnani surface, Periyar surface, Viyyam Surface and Kadappuram

Surface of age from Post Pliocene to Late Holocene respectively. In this paper we present

geomorphology of coastal segment from Vizhinjam to Kochi Vis-a Vis bathymetric variation

of the adjacent shelf. Location map of the study area is given (Fig. 1)

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Methods

Geomorphology of the coastal plain from Vizhinjam to Kochi was studied with aerial

photographs of scale 1: 16000. Ground truth was checked in necessary areas for confirmation

of geomorphologic features deduced from aerial photograph. Bathymetric chart (scale

1:1,500,000) published at the Naval Hydrographic office, Dehra Dun of the adjacent shelf

region of the Kerala coastal tract between Vizhinjam to Ponnani and highland contours in the

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chart up to Palghat gap was digitized and block diagrams of some important segments were

prepared using Surfer (V. 8).

Geomorphic Units

Following major geomorphic units were identified from the aerial photographs of scale

(1:16000) from Vizhinjam to Kochi.

a) Rocky cliffs: Cliffs of crystalline rocks are predominating in the coastal areas from

Vizhinjam to Kovalam. The cliffs are oriented in NNW - SSE direction i.e., the trends of

the cliffs and coastal lines are parallel (Fig. 2). The maximum elevation of the cliffs in

these regions is 80m. Resistant rocky exposures are seen as sea stacks near Vizhinjam and

Kovalam and such cliffs inhibit formation of beach except pocket beaches (e.g., Kovalam

beach).

b) Beaches: Wide sandy beach (~ 50 m. width), noticed north of Kovalam upto Kochi, is

interrupted by Tertiary exposures between Vakkom and Paravur. From Paravur to Kochi,

continuous stretch of beach is seen except for the barrier beaches developed at the mouth

of the estuaries. The beaches are straight with winter and summer berms. From

Ambalapuzha to Cherthala, the beaches are typically made up of silica sands, which are

mined for glassware manufacturing.

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c) Coastal Sandy Plain: This unit is prominent where there are extensive beaches. The

sandy plain marks the backshore region and extends up to an average width of 500m.

Sandy plain extends from north of Kovalam upto Vakkom and from Paravur to Kochi.

Maximum width for sandy plain (3 Km.) is acquired between Ambalapuzha and

Alappuzha stretches. Small dunes are also present in this sandy plain, but it cannot be

identified in the aerial photographs.

d) Estuaries and Lagoons: Kerala' landscape is blessed with estuaries and lagoons which

are confined along the coastal plains. The estuaries are popularly known as Kayals. The

Kayals in the Thiruvananthapuram - Kollam coastal stretch are Vellayani Kayal, Veli

Kayal, Kadinamkulam Kayal, Kozhithottam Kayal, Nadayara Kayal, Paravur Kayal, and

Ashtamudi Kayal. These Kayals except Vellayani Kayal form Type II Kayals (Joseph and

Thrivikramaji, 2002). The average length to width ratio of these Kayals is ~ 4.5. North of

Kollam, Kayamkulam Kayal and Vembanad Kayal are the prominent estuaries. The

lengths to width ratio of these Kayals are 6.5 ~. These belong to Type I Kayals of Joseph

and Thrivikramaji (2002).

e) Coastal Terraces: Tertiary sedimentary exposures along the coast from Vakkom to

Paravur resemble an uplifted terrace (Fig 3 &4). Maximum elevation of the terrace is 60

m. Other platforms like features appear at elevations of 20m and 40m. In Paravur

maximum elevation of the terrace is 40m. The Kayals of Types II and III (Joseph and

Thrivikramaji, 2002) are located in terrace at elevation <20m. Along the section between

Paravur and Edava a butte like feature is noticed (Fig. 3). These lateritic terraces extend

from the beach to inland for ~ 4 Km. and are parallel to the coastline, i.e. trending in the

NNW - SSE direction. Towards the eastern side, these are oriented in ENE - WSW

direction. This platform is exposed from Vakkom to Paravur.

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f) Sand Bars: Kerala coastline has sandbars of both large and medium scale dimensions.

Sandbars are found near the mouth of estuaries. Prominent sandbars are found at the

mouth of Veli Kayal, Nadayara Kayal, and Paravur Kayal, having an average length of

700 - 750 m. The longest sand bar (60Km.) can be noticed between Alappuzha and

Kochi with a maximum width of 10 Km (Nair, 1999). Ahamad (1985) proposed that the

sandbars formed as a result of the longshore drift from south to north in the coastal tracts

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of Kerala. Nair (1999) suggested that the sandbar along Alappuzha - Kochi coast is a

single bar and had been cut into two bars because of the strong monsoon winds.

g) Beach Ridges: This feature is also called as strandlines characterized by a number of

ridges - swale pattern. (Nair, 1987). The average length of strandline is reported as 50 -

500 m, width 30 - 500 m and a height of 2 - 10 m. The beach ridges of Kazhakuttam -

Kadinamkulam area are trending in the NNW - SSE direction. There are three sets of

strandlines in Karunagapally - Haripad area and four sets in Cherthala area, the eastern and

western most strandlines are oriented parallel to the coastline followed by NNE - SSW

and N - S direction respectively. Diverse orientations of strandlines indicate local

temporary fluctuations of sea level. There is an overall descent of the crestal levels of

these ridges towards the sea suggestive of progradation on an emerging coast, (Nair,

1999).

h) Mudflats: Ahamad (1985) explained the origin of mudflats due to the interaction between

the seawater and river mouth during monsoon, causes deposition of mud along the banks

of Kayals. Kerala coasts are devoid of extensive mudflat deposits. Small pockets of

mudflats occur in the wetlands of Kadinamkulam kayal, Ashtamudi kayal, Kayamkulam

kayal and Vembanad kayal.

i) Deltas: Older Deltaic plains, formed as a result of coalescence of two deltas of Manimala

and Pamba River are geologically and economically very important. This area extends

from the coastal sandy plain and extends up to the western margin of the lowland region

(i.e., elevation of 10-300m.). The delta (e.g. Kuttanad) resembles the shape of a bird's foot

(Nair, 1987). In aerial photographs, the sharp contact between the coastal sandy plain and

the deltaic plains can be clearly distinguished.

Offshore features

In general, continental shelf (up to 200 m isobath) off Kerala is narrow (av. width

~40Km). Profiles of selected transects (Fig. 5) show that shape of slopes of shelf edges vary

strikingly for the profiles of cliffed shorelines and noncliffed shorelines. In the cliffed portion

narrow shelf ends abruptly at the continental slope with a concave upward profile. Profiles on

the non-cliffed portion, north of Kollam, show a convex upward profile with gentle slope edge

(av. width 50Km). The ocean bottom topography (Fig. 6) of the southwestern part (Vizhinjam

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to Kollam) is different from the central part (Kollam to Kochi), which is characterized by a

wider shelf and a gentle seaward promontory called Alleppey platform (Singh and Lal, 1993).

Based on Gravity data, Arts, et al, (2003) explained Alleppey platform as a minor basement

high with variation in thickness of lower crustal layer characterized by a Moho rise below the

platform.

Evolution of Kerala Coast: A discussion

Kerala coast over a length of ~560 Km presents signatures of upliftment and submergence.

Evidences of emergence/submergence on ocean bottom topography upto shelf break are

explored in this study. Nair (1996, 2003) proposed a neotectonic theory for the evolution of

the coastal tracts of Kerala. The block diagram (Fig. 3 &4) along Vakkom

Varkala and

Edava

Paravur section suggests that the rate of uplift was not uniform, as indicated by three

sets of platform in the Tertiary exposure at Varkala and two sets at Paravur. The landward

dipping terraces indicate upliftment followed by faulting and tilting of the faulted block and

the floundering of other block forming the base of shelf. The bathymetry of the shelf shows a

nearly straight shelf edge, which is parallel to the shoreline. Striking feature on the south of

Kollam on the continental slope is a concave upward steep slope which is different from a

broad continental slope on the central region (north of Kollam) separated by Alleppey

platform. The coastline south of this platform is trending in the NW - SE direction while the

coastline north of this platform up to Alappuzha is trending in NNW- SSE direction. The

general trend of this platform is ENE - WSW direction which is coinciding with the lineament

seen along the Kerala coast. Nair (1996) proposed that the southern part formed by Warkallai

sedimentary formation was subjected to upliftment during post Mio - Pliocene time. The

authors could notice the occurrence of a patch of lateritised coral in Edava, at elevation ~5 m

above MSL. Kayals confined to the backshore of cliffed coastline resulted out of faulting

controlled by lineament tectonics (Joseph &Thrivikramji, 2002). These Kayals are flanked by

steeply hanging lateritic platforms along Paravur, Kappil and Ashtamudi Kayal.

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Broad and gently sloping shelf off Kollam-Kochi block suggests a prograding depositional

system due to excess sediment supply and subsequent subsidence. The tectonics of these

blocks in this region is controlled by lineaments cutting across the shorelines, which extend at

least east of Laccadive ridges (Kolla and Coumes, 1990 in Arts et al, 2003). The occurrence of

Warkallai formations and lateritic duricrusts was observed in boreholes drilled at 30-40m.

This depth attests to the subsidence of the basin after sub aerial weathering. The presence of

Tertiary clastics in the off shore regions of Kollam lend support to the down faulted segment

of the Tertiary basin (Nair, K.M. personnel comm.). Depositional features like wide beaches,

strandlines, mudflats, deltas, coastal sandy plains and Kayals of Type I (Joseph and

Thrivikramaji, 2002) characterize northern block. These Kayals form the typical lagoon -

barrier complexes with their axes parallel to the shoreline. Vembanad Estuary and beach

ridges might have been formed as a result of the formation of sand bars, which separated the

Arabian Sea and the trapped water of land during the transgression regression diachronism in

the late Holocene period (Kunte, 1995 Nair, 1996). The southern block can be classified as

narrow shelf with hilly coast and the northern block can be classified as narrow shelf with

plain coast (Inman and Nordstrom, 1971). Thus the uplift of Western Ghats results in the

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foundation of Tertiaries in the coastal areas and the neotectonic activity during the Quaternary

period has caused the present day Geomorphology.

Conclusion

The geomorphology of the Kerala s coast from south to north shows contrasting

features. Cliffs of crystalline rocks and Tertiary exposures predominate between Vizhinjam

to Paravur. From Paravur to Kochi, wide sandy beaches, strand lines, lagoons and mudflats

are the dominating geomorphic features. Striking feature of the south off Kollam on the

continental slope is a concave upward steep slope which is different from a broad continental

slope of Kollam

Kochi stretch separated by Alleppey platform. The geomorphic signatures

of south off Kollam indicate that this block is uplifted and the block north of Kollam is

subsided one. The uplifted block is exposed as platforms. Excess sediment supply and

subsidence causes progradation of the northern block.

Acknowledgement

The authors gratefully acknowledge the critical suggestions and support given by the

former Professor and Head of the Department of Geology Dr. K.P.Thrivivikramaji.

References

AHAMAD, E. (1985) Geomorphology, Kalyani Publishers, New Delhi, 403p.

ARTS, K.P., RADHAKRISHNA, M., MURTY, B.V.S., ARORA, S.K. and NAMBIAR,

C.G. (2003) Gravity Anomalies, Structure and Tectonics of the Kerala Basin, Southwest

Continental Margin of India. In: H.K. GUPTA and G.D. GUPTA, (eds.). Mem.54, Geol.

Soc. India, pp.203-216.

INMAN, D.L. and NORDSTORM, C.E. (1971) On the tectonic and morphologic

classification of coasts. Jour. Geol., v.79, pp.1-21

JOSEPH, S and THRIVIKRAMAJI. K.P. (2002) Kayals of Kerala Coastal Land and

Implication of Quaternary Seal Level Changes. In: A.C. Narayana (ed.). Late Quaternary

Geology of India and Sea level changes, Mem.49, pp.51-64.

12

NAIR, K. K. (1989) Quaternary geology and geomorphology in parts of Alleppey, Kottayam

and Pattanamthitta Districts, Kerala. Rec. Geol. Surv. Ind., v.122, pp.191-193.

KUNTE PRAVIN, D. (1995) On some aspects of barrier islands of the West Coast, India.

Jour. Of Coastal Research, Vol. 11, pp.508-515.

NAIR, K. K. (2003) Morphostratigraphy, age and evolution of coastal plain landforms of

Kerala, Proc of Geosas - IV, pp.63-70.

NAIR, K.K. (1996) Geomorphology and evolution of coastal plain of Kerala. Geo. Surv. Ind.

Spl. Pub. No.40, pp. 83-94.

NAIR, M.M, and SUBRAMANIAN, K.S. (1989) Transform faults of the Carlsberg Ridge-

their implication in neotectonic activity along the Kerala coast. Geol. Surv. India, Spl. Publ.

No.24, pp.327-29.

NAIR, M.M. (1987) Coastal geomorphology of Kerala. Jour. Geol. Soc. India, v.29, pp.450-

458.

NAIR, M.M. (1990) Structural trendline patterns and lineaments of the Western Ghats, South

of 130 latitude. Jour. Geol. Soc. India, v.35, pp.99-105.

NAIR, M.M. (1999) Quaternary coastal geomorphology of Kerala. Indian Jour. Of

Geomorphology, v.4, pp.51-60.

RAHA P. K., SINHA- ROY, S. and RAJENDRAN, C. P. (1983) A new approach to the

Lithostratigraphy of the Cenozoic Sequence of Kerala. Jour. Geol. Soc. India, v. 24, pp.325 -

342.

13

RAJENDRAN, C.P., RAJAGOPALAN, G. and NARAYANASWAMY. (1989) Quaternary

Geology of Kerala; Evidence from Radiocarbon Dates. Jour. Geol. Soc. India, v. 33, pp.218-

222.

PRABHAKAR RAO, P., NAIR, M.M.. and RAJU, D.V. (1985) Assessment of role of the

remote sensing techniques in monitoring shoreline changes. A case study of Kerala coast.

Intr. Jour.Remote sensing, v.6, No.3&4,pp.549-558.

SINGH, N.K. and LAL, N.K. (1993) Geology and petroleum prospects of Konkan

Kerala

basin, Proc. Second Sem. Petroliferous basins India.2nd Ed.S.K.Biswas et.al, Indian Petroleum

Publisher, Dehradun.

SOMAN, K., CHATTOPADHYAY, M., CHATTOPADHYAY, S and KRISHNAN POTTI,

G. (2002) Occurrence and Water Resource Potential of Fresh Water Lakes in South Kerala

and their Relation to the Quaternary Geologic Evolution of the Kerala Coast. In: A.C.

Narayana, Late Quaternary Geology of India and Sea level changes, Mem.49, Geol.Soc.India,

pp.17-29.

SOMAN, K. (2002) Geology of Kerala. Geological Society of India, Bangalore, 335p.

SUCHINDAN, G.K, SHAMSUDDIN, M. and THRIVIKRAMAJI, K.P (1987) Coastal

Geomorphology and Beach Erosion and Accretion in the Northern Kerala Coast. Jour. Geol.

Soc. India, v.29, pp.379-389.

THRIVIKRAMAJI, K.P., ANIRUDHAN, S. and NAIR, A. S. K (1983) Shoreline fluctuation

in Kerala - retrospect, perspect and prospect. In: Nambiar (Ed.), Proceedings of the seminar

on management of the environment, Engineering College, Trichur, Kerala, pp.58-62.

VARADARAJAN, K. and NAIR, K.M. (1978) Stratigraphy and Structure of Tertiary Kerala

Basin. Jour. Geol. Soc. India, v.19, pp.217-220.

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