Indira Point Lighthouse: 4.25 m of subsidence in the 26 Dec 2004 earthquake

Indira Point 6°45.2'N 93°49.6'E Height of tower above mean sea level=35 m. Height of iron pillar=30 m. Extract Copyright © 2001 Office of The Director General Of Lighthouses and Lightships,Andaman & Nicobar. June 23, 2001

"The Lighthouse is situated on the Southern most tip of the Indian Territory and is an important landfall for the international shipping, sailing through Malaccia strait towards Singapore.  The equipment manufactured by M/s BBT, Paris and consisting of revolving 3rd order optic mounted on mercury float pedestal and housed inside the lantern was installed in 1972.  The optic was rotated by gas motor. The Lighthouse was inaugurated and commissioned into service on 30th April 1972 by the then Vice President of India, Mr.G.S.Pathak. It was known as Pygmalion point Lighthouse previously. It was renamed in honour of Mrs. Indira Gandhi. 

Due to heavy salinity, the gas motor revolving system did not work and the optic was replaced by 500mm cut and polished drum optic and DA gas burner with flasher and sun-valve in 1978. Subsequently with the DA Gas supply becoming irregular, the gas flasher was replaced by Halogen lamp and Electronic Timer operating on solar charged batteries, on 28th February 1996.  The ‘Racon’ (Marconi)was installed on the Lighthouse Tower on 25th February 1985.

            The Radio beacon (MACE) equipment has been installed at the station in November 1999. Simultaneously the drum optic and light source have been replaced by 300mm revolving 4 panel optic and 400W Metal Halide lamp. The system is functioning on experimental basis and is expected to be commissioned in January 2000."

COMMENTARY: The "inland" view (from near former sea level) shows the lighthouse surrounded by huts and trees that are now gone. The 'flooded" view offshore (viewed from new beach level) was taken by the Indian Coastguard after the earthquake and shows the base, inferred in 1972 to have been constructed 5 m above sea level, to now be less than 1 m above instantaneous sea level. The uncertainty in estimating its base depends on whether the lighthouse data indicate the height of the light axis in both estimates, or generic details of construction. The height of the tidal stage in the recent photo is unknown. With these caveats one may estimate subsidence at Indira Point as little as 2 m or as much as 4.5 m.

A deputy director in the Department of Lighthouse and Lightships provides independent confirmation of this estimate. The base of the Indira point lighthouse is claimed to have been 3.5m above sea level before 26th Dec 2004. In January 2005 the base of the lighthouse was level with low tide and 1.5m below sea level at high tide.i.e. 0.75 m below approximate mean sea level.

We conclude that the southern end of Great Nicobar island has subsided 4.25±0.2 m. A more precise measurement must await the availability of instrumental measurements of mean sea level.

Lighthouses at Katchal East, Katchal West, and Interview Island are reported "completely destroyed". Post-seismic photographs are unavailable at present, but if reduction to rubble is true, it would suggest MSK intensity IX shaking both in the western Nicobars and in the north-western Andamans since these lighthouses were well-constructed masonry pillars, 10 m high, symmetrical and with wide aspect-ratio.