The Waters around Sri Lanka
Friday, November 20th, 2020 | Blog
The Indian Ocean as a whole has a mean depth of 3,900m, increasing to a maximum of about 8,000m. Within the 200-nautical-mile (370km) radius of Sri Lanka’s exclusive economic zone, its maximum depth is about 6,000m.
The continental shelf on which the island sits has a mean depth of 75m and forms part of the Asian continent. Around Sri Lanka it is relatively narrow, rarely extending beyond 22km (12nm), pinching in off Kalpitiya Peninsula near Puttalam, and cut by submarine canyons off Dondra Head, Trincomalee, Batticaloa and several other points along the east coast.
The shelf is narrowest off Trincomalee, where a giant submarine canyon makes its closest approach to land, and widest off the Jaffna peninsula at Point Pedro, where it extends outward for 60km (32nm).
Sandstone reefs, often following the bathymetric contours of the continental shelf, are a common navigational hazard in Sri Lanka’s coastal waters. Seagrass beds often occur in proximity to coral reefs, estuaries and lagoons. Such beds form the main habitat of the dugong that inhabit Palk Bay and the coastal waters north of Kalpitiya.
Other important oceanographical features around Sri Lanka include Adam’s Bridge, a chain of shoals and sandbars that connects the north of the island with India; the Gulf of Mannar (part of the Laccadive Sea), which separates the two countries and is bounded by Adam’s Bridge to the north and the southern tip of India to the west; and the Bay of Bengal inlet, including Palk Bay and Palk Strait, which also separates the two countries and is bounded by Adam’s Bridge to the south.
Further away are the Chagos-Laccadive Ridge, 750km (400nm) west of Sri Lanka, whose peaks rise above sea level to form the Chagos, Laccadive (Lakshadweep) and Maldive island chains and the Ninety East Ridge, a gigantic submerged mountain range that rises 830km (450nm) east of Sri Lanka and stretches southward as far as the Horse Latitudes.
Beyond the continental shelf, other ridges and seamounts rise from the ocean floor. In the Laccadive Sea, a mid-ocean ridge and several seamounts lie between the west coast of Sri Lanka and the Chagos-Laccadive Ridge. This area was known to olden-day whalers as a haunt of sperm whales.
Text by Howard Martenstyn, Out of the Blue