Morphology of the Continental Shelf around South India and Sri Lanka

Let us quickly summarise the notable features of the Continental Shelf (CS):

A) Comparison of Width

1. The CS of the east coast is much narrower than that of the west and the southern coasts of India.

2. The land mass of India and Sri Lanka are linked to each other in-continuum by the CS at northern portion of Gulf of Mannar (GOM), Adam's Bridge (AB), Palk Bay (PB) and Palk Strait (PS).

3. The CS around Sri Lanka in general is very narrow. However, the CS of the northern and north - western coast of Sri Lanka is broader.

4. The provisional measurements of the shelf break of CS above are as follows:

a) North eastern coast stretching from Palar estuary to Chennai - 40 to 50 km

b) CS adjoining Marakkanam - Palar Estuary stretch - ----------- 20 km

c) CS adjoining Poompuhar - Pondicherry ----------------------- 10 to 20 km

d) CS adjoining Vedaranyam - Karaikal -------------------------- 80 to 20 km

e) Point Pedro -------------------------------------------------- 40 km

f) Mullaitivu ---------------------------------------------------- less than 10 km

g) Trincomalee ------------------------------------------------- less than 3 km

f) Batticola ------------------------------------------------------ 5 km

g) Pottuvil --------------------------------------------------- 5 km

h) Galle - Colombo stretch--------------------------------------- 10 km

i) Tuticorin to Kudankulam -------------------------------------- 20 km

j) Cape Comorin to Colachal -------------------------------------- 120 to 160 km

k) Trivandrum --------------------------------------------------- 40 to 50 km

l) Kollam --------------------------------------------------------- 70 km

m) Ernakulam ---------------------------------------------------- 40 to 50 km

B) Alignment pattern of the CS in the various regions:

1. Palar to Chennai stretch is aligned in the N-S direction. It falls to 100 - 130 meters depth gradually over a distance of 40 to 50 km. From then on, the CS falls steeply to a depth of 2000 meters within a span of say 10 km.

2. Marakkanam to Palar estuary stretch is aligned in a NE-SW direction. The CS falls gradually for about 20 km at Marakkanam, then it dips suddenly to 1000 meters within a distance of 10 km, then the sea bed slopes gradually to 2000 meters over a distance of say 60 to 70 km.

3. Poompuhar to Pondicherry stretch is aligned in the N-S direction. The CS falls steeply from the shoreline to 1000 meters with in a spsn of say 10 km. However, the sea bed dips gradually from thereon, to reach a depth of 2000 meters in a span of 40 km.

4. The features of the Karaikal to Vedaranyam stretch is remarkably interesting. Here, the shoreline is aligned in the N-S direction. However, the CS is aligned in a NW - SE direction. CS at this stretch is like a flat table, whose brim is located at say 20 km from the Karaikal shoreline and at say 80 km from the Vedaranyam - Kodikkarai shoreline. The depth at which this CS is located is sub 20 meters. From this depth the CS taks a vertical dive to a depth of 2000 meters in a span of 5 to 10 km.

5. Point Pedro shoreline is aligned WNW - SE, whereas its CS is aligned NW - SE. The shape and depth of this region's CS is similar to the Karaikal - Vedaranyam CS stretch. It is flat and stretches to a distance of say 40 km. It also, like the previous region, falls from a depth of 20 m to 2000 m within a span of say 5 km.

6. Mullaitivu to Pottuvil shoreline is aligned NW-SE. The CS is also aligned similarly. The CS runs flat to east for about 5 to 10 km. From there it falls steeply to a depth of 2000 m within a span of 5 km.

7. The sea bed of Gulf of Mannar is step like.

8. The CS of the south coast of Sri Lanka is broader in the east ( say 10 to 30 km) (around Hambatota) and narrower in the west (say 5 km). The CS falls gradually over this distance initially, then dips to a depth of 3000 m, in a span of 20 km. There is no much difference between the alignment of the shoreline and the CS in this region.

9. The shoreline and the CS of the Galle - Colombo stretch is aligned in the S-N direction. The fall of the CS is gradual for a span of say 10 km, which falls steeply to 2000 meters at Galle, to 1000 m at Colombo within a span of 10 km.

10. The stretch between Colombo and Puttalam is simililar in all aspects except that the CS falls only to a depth of 500 m here.

11. The region of CS located north of Puttalam is the region that comprises of the northern portion of Gulf of Mannar, Adam's Bridge and Palk Bay. This CS is flat and tabletop like and its depth varies between say 5 to 100 meters. The CS keeps both the land masses of South India and Sri Lanka in continuum.

12. The shoreline and the CS between Tuticorin and Tiruchendur are aligned almost in the N-S direction. The CS falls gradually over a distance of 20 km initially, then dips steeply to a depth of 500 m with in a span of 5 km.

13. The shoreline between Tiruchendur and Cape Comerin is aligned in the ENE-WSW direction. However, the CS is aligned NE-SW direction. The CS is flat here, and stretches to a distance of say 20 to 60 km initially. It taks a dip to 500 meters then within a span of say 5 km.

14. The CS of Cape Comerin - Colachal stretch is flat and table top like. Up to a distance of 120 to 160 km, the sea depth is sub 100 meters. Beyond this distance, the CS falls steeply to a depth of 1000 meters within a span of 10 km.

15. The CS of the south western coast of South India that stretches between Colachal to Ernakulam is flat, and the CS break occurs at a distance of say 40 (Trivandrum and Ernakulam) to 70 km (Kollam) from the shoreline. The CS then dips steeply to a depth of (only) 500 meters, in a span of another 5 to 10 km.