Thursday, March 26, 2009

The Power Of An Image- Western Ghat Escarpment

Sometimes an image has the power to stop you in your tracks. I look at images all the time, mostly satellite images, sometimes old aerial photos. A few minutes ago I was mucking around looking for elevation data on India, and tucked in a folder I hadn't browsed for a while was a USGS GTOPO30 DEM. This is a DEM with a horizontal grid spacing of 30 arc second which is about 1 km.

I imported the surface in Manifold GIS. A quick thematic display using the standard Altitude palette, but the result was breathtaking. Below is the western ghat escarpment stretching from north of Mumbai to south of Goa. That's more than 400 km. Its made up of the Deccan basalts along most of the extent of this image but just north of Goa the basalts pinch out and the Precambrian shield region begins.

It goes on for some distance to the south right up to the state of Kerala, but I had to juggle the extent so as to find the right balance between showing it's impressive span but still to be close enough for the sharp topographic divide between the coastal plains and the plateau to come through.

It does so in a marvelous fashion. The darker green coastal plains crash against, almost seem to subduct underneath the long wriggly escarpment, its shadow highlighting the near vertical relief. The local relief is spectacular, more than 1000-1500 feet cliffs and gorges. The escarpment is the edge of an uplifted and east tilted plateau. As a result all the major rivers of peninsular India in this region have easterly drainage. The drainage is antecedent. Post Deccan volcanic but before western ghat uplift. As a result there are meandering gorges and drainage cutting across gentle fold axis.

I was in a hurry to post this. I didn't project the surface, left it in geographic co-ordinates. The scale says 1 deg which is about 110 km at equator.

I travel across the escarpment often. In a car it takes about 20 minutes to an hour to cross depending upon where along its length you are making the crossing. The climatic contrast between the warm humid coastal plains and the dry cooler plateau is noticeable and in summers desirable. You can trek across it too along some pretty demanding trails or try to mountaineer the sheer cliffs.

Now that would be an experience!

It's one of the great geological features I have witnessed and I live about an hour's drive from it.


  1. I bet you must have heard about "Konkan Kada", near Malshej, on way from Mumbai to Ahmednagar.
    The intimidating rock-cliffs along the Sahyadris are a treat to watch, both for non-geologist, as well for academic interest.

  2. Konkan Kada is spectacular. Is that the one near Harishchandragad?

  3. Yes, the one near Harishchandra-gad :)